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Kendl, Alexander. "Driftwellen in Helias-Konfigurationen." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=959973532.
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Unemura, Takeshi. "Nonlinear Behavior of Pressure Driven Modes in Stellarator Plasmas." Kyoto University, 2003. http://hdl.handle.net/2433/148650.
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Kyoto University (京都大学)0048
新制・課程博士
博士(エネルギー科学)
甲第10332号
エネ博第68号
新制||エネ||20(附属図書館)
UT51-2003-H753
京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻
(主査)教授 前川 孝, 教授 近藤 克己, 助教授 浜口 智志
学位規則第4条第1項該当
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Zhang, Yangyang. "Three Dimensional Physics in Reversed Field Pinch and Stellarator." Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3426218.
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This dissertation is dedicated to the study of three dimensional transport in toroidal magnetic configurations induced by the presence of the magnetic islands, which break the nested flux surfaces and make the magnetic field intrinsically three dimensional. The methodology applied is based on defining a certain symmetry so that the transport study could be performed in the approximation of 1.5 dimensions. The work has been carried out on both RFX-mod Reversed Field Pinch (RFP) and the TJ-II stellarator.
RFX-mod is the largest RFP in the world. The RFP configuration is sustained by the so-called dynamo mechanism, which is related to the non-linear interactions among many resonating MHD tearing modes. The transport study on RFX-mod has been performed on the three sub-states identified in the Quasi-Single Helicity regime, that features one single mode (dominant mode) dominating the mode spectrum, while the rest of the modes (secondary modes) remain at low amplitudes. In this regime proper flux coordinates can be identified considering an equilibrium built on the underlying axi-symmetric magnetic field plus the contribution from the dominant mode. In this way, a 1.5 dimensional approximation transport study is possible by averaging different physical quantities over the flux surfaces. The transport study is focused on the bean-shaped region where nearly conserved flux surfaces have been identified, on which the formation of steep thermal gradients is observed, interpreted as electron Internal Transport Barrier (eITB). Starting from experimental measurements, both the thermal gradients and the thermal diffusivity have been calculated and their behaviors have been discussed within the framework of stochastic transport. Finally, the energy confinement time has also been evaluated, adopting an improved method with respect to past studies, and the results show a significant improvement.
The transport study on TJ-II stellarator focuses on the calculation of the enhanced non-ambipolar radial electric field due to the presence of the magnetic islands. The main idea of the study is that the magnetic islands could modify the toroidal plasma viscosity, giving rise to an enhancement on the non-ambipolar particle fluxes. This work started with the study of the Neoclassical Toroidal Viscosity developed by K. C. Shaing for tokamak configurations, which ideally has a toroidal symmetry. Applying this theory, the particle flux can be expressed as a function of a monotonic radial coordinate and thus the transport study could be performed with a 1.5-dimensional approach. A moderate modification on the original theory has been made and the corresponding justification is presented, together with the detailed study in both tokamak and TJ-II configurations. The results show that an 'extra' local radial electric field is indeed induced by the magnetic islands in TJ-II plasmas, which could play a positive role in the plasma confinement properties by affecting the L-H transition, which is believed to be strongly linked to the shear of E x B flow.Questo lavoro di tesi è dedicato allo studio degli effetti tridimensionali sul trasporto indotti dalla presenza di isole magnetiche in configurazioni toroidali per il confinamento magnetico. Le isole magnetiche producono la rottura delle superfici magnetiche annidate dando al campo magnetico caratteristiche intrinsecamente tridimensionali. La metodologia pplicata si base sulla possibilità di definire un certo livello di simmetria in maniera tale da poter studiare il trasporto nell’approssimazione di 1.5 dimensioni. Lo studio è stato fatto sul Reversed Field Pinch (RFP) RFX-mod e sullo stellarator TJ-II. RFX-mod è il più grande RFP al mondo. La configurazione RFP è sostenuta dal meccanismo della dinamo, che è legato all’interazione non-lineare dei molti modi tearing risonanti. Lo studio del trasporto in RFX-mod è stato eseguito sui tre sotto-stati identificati nel regime a Quasi singola Elicità, il quale è caratterizzato da un singolo modo (modo dominante) che risulta dominante nello spettro dei modi, mentre gli altri modi (modi secondari) mantengono un’ampiezza ridotta. In questo regime, sono identificabile delle coordinate di flusso magnetico basate sulla combinazione dell’equilibrio assial-simmetrico sottostante con il contributo del modo dominante. In questa modo un approccio 1.5 dimensionale allo studio del trasporto è possibile considerando la media sulle superfici di flusso delle varie quantità fisiche. Lo studio del trasporto è riferito alla regione a forma di fagiolo dove è possibile identificare delle superfici di flusso quasi conservate dove si osserva la formazione di ripidi gradienti termici, interpretabili come barriere interne di trasporto elettronico (ITB). A partire dalle misure sperimentali, sono stati calcolati sia i gradienti termici che il coefficiente di diffusione termica e il loro andamento è stato discusso nell’ambito del trasporto stocastico. Alla fine è stato anche calcolato il tempo di confinamento dell’energia, utilizzando un metodo migliorato rispetto a quanto fatto in passato, dimostrando un significativo miglioramento delle prestazioni del plasma. Lo studio del trasporto nello stellarator TJ-II si è concentrato nel calcolo dell’aumento del campo elettrico non-ambipolare dovuto alla presenza di isole magnetiche. L’idea alla base dello studio si basa sul fatto che un’isola magnetica potrebbe modificare la viscosità toroidale del plasma, aumentando in questo modo il flusso non-ambipolare delle particelle. Lo studio è partito dall’analisi del modello neoclassico di viscosità toroidale sviluppato da K.C. Shaing per la configurazione tokamak, che idealmente possiede una simmetria toroidale. Applicando questa teoria, il flusso di particelle può essere descritto in funzione di una coordinata radiale monotona e quindi lo studio del trasporto può essere affrontato nell’approssimazione 1.5 dimensionale. E’ stato necessario considerare una parziale modifica della teoria originale la cui giustificazione viene presentata assieme allo studio dettagliato sia nella configurazione tokamak che nello stellarator TJ-II. I risultati mostrano che un campo elettrico radiale ‘aggiuntivo’ è effettivamente indotto da un’isola magnetica nei plasmi di TJ-II. Questo potrebbe giocare un ruolo positivo nelle proprietà di confinamento del plasma, influenzando la transizione L-H, che si ritiene sia fortemente legata allo shear del moto ExB.
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Kauffmann, Karla [Verfasser]. "Including Collisions in Gyrokinetic Tokamak and Stellarator Simulations / Karla Kauffmann." Greifswald : Universitätsbibliothek Greifswald, 2012. http://d-nb.info/1021840904/34.
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Hakso, H. (Heidi). "Nuclear fusion energy and comparison of tokamak and stellarator reactors." Bachelor's thesis, University of Oulu, 2018. http://urn.fi/URN:NBN:fi:oulu-201805261943.
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This bachelor’s thesis presents the basic principles of nuclear fusion energy, its sustainability and compares the two most prominent fusion reactors; tokamaks and stellarators. Work is done through a literature review. Topic is relevant because energy demand is increasing and environmentally friendly ways of producing energy are needed. Fusion energy could have potential to produce vast amounts of pollution free energy without the long-lived radioactive waste or the risk of runaway reactions. However, fusion reactors have not yet been able to prove their feasibility in power generation due to its challenging physics and technology. Fusion and fission are nuclear reactions. In fusion, light atoms fuse together whereas in fission heavy atoms break apart. The reactions produce energy based on the nuclear binding energy as the created atoms are more stable i.e. have a greater binding energy than the initial ones. Produced energy is related to the created mass defect between the nuclei and the separate nucleons. Fusion reactions happen inside plasma. Temperature, density and confinement of plasma, i.e. triple product, need to reach high enough values for fusion to work. Both tokamaks and stellarators use magnetic confinement as plasma is electrically charged and can be controlled with magnetic fields. Magnetic configurations set the two reactors apart. Tokamaks have toroidal and poloidal superconducting magnetic coils. They also have a transformer creating an electric current in the plasma. Their biggest advantage is their symmetrical and simple structure, but a big disadvantage is the transformer-driven current that forces tokamaks to work only in pulses. Stellarators have only magnetic coils and no current inside the plasma. To ensure plasma confinement, their structure is helically twisted and non-axisymmetric making the complicated structure their biggest disadvantage. Lack of current makes them work continuously, which is their biggest advantage. ITER’s tokamak in France and IPP’s Wendelstein 7-X stellarator in Germany show the current state of fusion research. These are used as examples in the thesis. Currently tokamaks are more advanced and closer in generating more energy than is needed to heat the plasma. As plasma physics evolves and the stellarator instabilities are fixed, their continuous operation might make them more viable for the futureTämä kandidaatintyö esittelee ydinfuusioenergian perusperiaatteet, sen kestävyysnäkökulmat, ja vertailee kahta lupaavinta reaktoria; tokamakia ja stellaraattoria. Työ on kirjallisuuskatsaus. Aihe on ajankohtainen, sillä energiantarve kasvaa ja ympäristöystävällisempiä energiamuotoja tarvitaan. Fuusioenergialla on potentiaalia tuottaa suuria määriä päästötöntä energiaa ilman pitkäikäistä radioaktiivista jätettä tai suurien ydinonnettomuuksien riskiä. Fuusioreaktorit eivät vielä ole onnistuneet todistamaan fuusiovoimaloiden toteutettavuutta johtuen fuusion haastavasta fysiikasta ja teknologiasta. Fuusio ja fissio ovat ydinreaktioita. Fuusiossa kevyet atomit sulautuvat yhteen ja fissiossa raskaat atomit hajoavat pienemmiksi. Reaktiot tuottavat energiaa johtuen sidosenergiasta, kun syntyneet atomit ovat vakaampia eli omaavat korkeamman sidosenergian kuin alkuperäiset. Syntynyt energia voidaan laskea massavajeesta atomiytimien ja erillään olevien nukleonien välillä. Fuusioreaktiot tapahtuvat plasmassa. Plasman lämpötilan, tiheyden ja koossapitoajan eli kolmitulon tulee saavuttaa riittävän korkeat arvot, jotta fuusio voi onnistua. Tokamakit ja stellaraattorit molemmat käyttävät magneettista koossapitoa, sillä plasma on sähköisesti varautunutta ja siten sitä voidaan kontrolloida magneettikenttien avulla. Magneettien kokoonpano on reaktorien suurin eroavaisuus. Tokamakeissa on toroidaalisia ja poloidaalisia suprajohtavia magneettikeloja. Niissä on myös muuntaja, joka luo sähkövirran plasmaan. Tokamakien suurin etu on niiden symmetrinen ja yksinkertainen rakenne, mutta muuntajan tuottaman epäjatkuvan virran takia voivat ne toimia vain pulsseissa. Stellaraattorit käyttävät vain magneettikeloja, ilman sähkövirtaa plasmassa. Varmistaakseen plasman koossapidon, ovat stellaraattorit epäsymmetrisiä ja kierteisiä. Muuntajan poissaolon takia niiden suurin etu on mahdollisuus jatkuvatoimisuuteen. Suurin haitta stellaraattoreilla on kuitenkin niiden monimutkainen rakenne. ITERin tokamak Ranskassa ja IPP:n stellaraattori Wendelstein 7-X Saksassa kuvaavat hyvin fuusioreaktoreiden tutkimuksen nykytilaa. Nämä reaktorit ovat esimerkkeinä tässä työssä. Tällä hetkellä tokamakit ovat kehittyneempiä ja lähempänä tuottamaan enemmän energiaa kuin mitä plasman lämmittämiseen tarvitaan. Kun plasmafysiikka kehittyy ja stellaraattorien epävakauksia korjataan, voi jatkuvatoimisuus tehdä niistä paremman vaihtoehdon tulevaisuuteen
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Ichiguchi, Katsuji. "Numerical Studies of Three-Dimensional Equilibrium and Stability for Stellarator/Heliotron Configurations." Kyoto University, 1989. http://hdl.handle.net/2433/74743.
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Empacher, Lars. "Analyse eines Vielstrahl-Wellenleiters zur Übertragung hoher Mikrowellenleistungen." [S.l.] : Universität Stuttgart , Fakultät Elektrotechnik, 1999. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB8287462.
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Sichardt, Gabriel [Verfasser], and Thomas [Akademischer Betreuer] Hirth. "Electron cyclotron emission investigations at the stellarator TJ-K / Gabriel Sichardt ; Betreuer: Thomas Hirth." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2020. http://d-nb.info/1212034597/34.
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Rakha, Allah. "Analysis of energetic particle-driven Alfvénic instabilities in tokamak and stellarator plasmas using three dimensional numerical tools." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/671252.
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In this thesis, a detailed analysis of the experientially observed energetic particle-driven Alfvénic instabilities in tokamak and stellarator plasmas using three dimensional numerical tools based on the reduced MHD model has been carried out. In TJ-II stellarator plasmas, modelling of chirping and steady modes assesses their coexistence on the persistent appearance of the corresponding combination of the toroidal (n) and poloidal (m) mode numbers through the rotational transform sensitivity analysis both in iota lowering and iota rising dynamic plasmas. Modelling of the experimentally observed frequency sweeping phenomenon during the presence of Alfvénic activity with radially extended low-shear and radially localized strong-shear non-monotonic (NM) iota profiles provides an extended spectrum of Alfvénic modes in the wide frequency range as compared with normal (monotonic) iota profile results. Comparison of mode frequencies calculated using a standard dispersion relation and those modelled with the reduced MHD clustered frequency solver AE3D shows an agreement with the selection of iota minimum values, which supports MHD spectroscopy calculations.
Wave particle interaction (WPI) studies for the resonance function calculations developed using Monte Carlo transport model based on the 3D MHD equilibria for the TJ-II plasmas suggest for low bounce harmonics (p) the possibility of describing the non-linear evolution of the AEs in TJ-II by a sum of two ion populations with different weighting factors, one of which is dominated by drag and the other by diffusion. As the bounce harmonic increases, the resonance region starts to expand and can cover a significant area of the particle phase space until this resonance region vanishes at high bounce harmonics.
In ASDEX Upgrade tokamak plasmas a bifurcated MHD equilibrium is reconstructed with formation of 3D helical core as saturated magnetic axis and the remaining torus with an axisymmetric equilibrium. The formation of helical core is characterized as an 3D perturbation in an axisymmetric equilibrium state. Helically distorted MHD equilibria exit for the axisymmetric devices if q = 1 rational surfaces are present. Alfvén continuum calculations with the bifurcated equilibria lead to the frequency splitting between the highest frequency branch and the lowest frequency branch continua at the frequency accumulation point. Radially localised shifting of modes happens via coupling of the adjacent n-1 continuum around an accumulation point. Modelling including 3D effects correctly reproduces the phenomenon of continuum frequency splitting and provides a possible solution for the differences of few kHz in frequency splitting, which remained unexplained with the 2D kinetic calculations. The pressure scaling confirms the increase of helical excursion of the magnetic axis in equilibrium reconstruction and hence the range of continuum frequency splitting. The existence of low-frequency continua and its splitting around the frequency accumulation point are in agreement with the experimental observations for the low-frequency modes.
This dissertation provides an extensive comparison of the experimental and modelling results for the TJ-II stellarator plasmas along with the effect of the formation of bifurcated MHD equilibria on Alfvén continua in AUG tokamak plasmas.En esta tesis, se ha llevado a cabo un análisis detallado de las inestabilidades Alfvénicas de partículas energéticas observadas experimentalmente en plasmas de tokamak y stellarators utilizando herramientas numéricas tridimensionales basadas en el modelo MHD reducido. En los plasmas de estellarators de TJ-II, el modelado de chirping y modos estables evalúa su coexistencia en la aparición persistente de la combinación correspondiente de los números de modo toroidal (n) y poloidal (m) a través del análisis de sensibilidad de transformación rotacional tanto en disminución de iota como en aumento de iota. El modelado del fenómeno de barrido de frecuencia observado experimentalmente durante la presencia de actividad Alfvénica con perfiles de iota no monotónicos (NM) de cizallamiento fuerte y de cizallamiento fuerte radialmente extendido proporciona un espectro extendido de modos Alfvénicos en el amplio rango de frecuencia en comparación con el normal (monotónico). La comparación de las frecuencias de modo calculadas usando una relación de dispersión estándar y aquellas modeladas con el solver de frecuencia agrupada para MHD reducido AE3D muestra un acuerdo con la selección de valores mínimos de iota, que respalda los cálculos de espectroscopía MHD. Los estudios de interacción de onda-partículas (WPI) para los cálculos de la función de resonancia desarrollados utilizando el modelo de transporte Monte Carlo basado en los equilibrios 3D MHD para los plasmas TJ-II sugieren para armónicos de bajo rebote (p) la posibilidad de describir la evolución no lineal de los AE en TJ-II por una suma de dos poblaciones de iones con diferentes factores de ponderación, uno de los cuales está dominado por arrastre y el otro por difusión. A medida que aumenta el armónico de rebote, la región de resonancia comienza a expandirse y puede cubrir un área significativa del espacio de fase de partículas hasta que esta región de resonancia se desvanece en armónicos de alto rebote. En los plasmas del ASDEX Upgrade tokamak se reconstruye un equilibrio MHD bifurcado con formación de núcleo helicoidal 3D como eje magnético saturado y el toro restante con un equilibrio axisimétrico. La formación del núcleo helicoidal se caracteriza como una perturbación 3D en un estado de equilibrio axisimétrico. Los equilibrios MHD distorsionados helicoidalmente salen para los dispositivos axisimétricos si en q = 1 están presentes superficies racionales. Los cálculos continuos de Alfvén con los equilibrios bifurcados conducen a la división de frecuencia entre la rama de frecuencia más alta y la rama de frecuencia más baja continua en el punto de acumulación de frecuencia. El cambio de modos radialmente localizado ocurre mediante el acoplamiento del continuo n-1 adyacente alrededor de un punto de acumulación. El modelado que incluye efectos 3D reproduce correctamente el fenómeno de la división de frecuencia continua y proporciona una posible solución para las diferencias de pocos kHz en la división de frecuencia, que permaneció sin explicación con los cálculos cinéticos 2D. La escala de presión confirma el aumento de la excursión helicoidal del eje magnético en la reconstrucción de equilibrio y, por lo tanto, el rango de división de frecuencia continua. La existencia de continuas de baja frecuencia y su división alrededor del punto de acumulación de frecuencia están de acuerdo con las observaciones experimentales para los modos de baja frecuencia. Este estudio se compone de una comparación extena de los resultados experimentales y de modelaje para los plasmas del stellarator TJ-II junto con el efecto de formación del equilibrio MHD bifurcado en el continuo Alfvén en los plasmas del AUG tokamak.
(Neerlandès) De experimenteel waargenomen Alfvénic-instabiliteiten die in tokamak- en stellaratorplasma's aangedreven worden door snelle deeltjes worden in detail geanalyseerd. De analyse gebeurde met behulp van driedimensionale numerieke methodes gebaseerd op het gereduceerde MHD-model. In TJ-II stellarator plasma's werd de co-existentie van tjilpende (chirping) en steady-state modi vastgesteld op basis van het aanhoudend voorkomen van de overeenkomstige combinatie van de toroïdale (n) en poloidale (m) modenummers. Deze vaststelling gebeurde op basis van de gevoeligheid ten opzichte van de rotatie-transformatie (rotational transform). Modellering van de veging van de frequentie (frequency sweeping) van de Alfvénic-activiteit met niet-monotone iota-profielen zijn, in vergelijking met normale (monotone) iota-profielresultaten, consistent met experimentele resultaten. Studies van de interactie tussen golf en deeltjes (WPI-wave particle interaction) voor de berekening van de resonantiefunctie met behulp van Monte Carlo transportmodel voor TJ-II plasma's, suggereren dat de niet-lineaire evolutie van AE's een som is van twee ion populaties met verschillende wegingsfactoren. Voor lage bounce harmonische, wordt één gedomineerd door sleep (drag) en de andere door diffusie. In ASDEX Upgrade tokamak-plasma's wordt een vertakt MHD-evenwicht gereconstrueerd met de vorming van een 3D-spiraalvormige kern en de asymmetrische 2D-mantel. Alfvén continuümberekeningen met de vertakte evenwichten leiden tot de frequentiesplitsing tussen de continua van de hoogste frequentietak en de laagste frequentietak en het verschuiven van modi met aangrenzend n continuüm rond het frequentieaccumulatiepunt.
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Häußler, André [Verfasser], and R. [Akademischer Betreuer] Stieglitz. "Computational approaches for nuclear design analyses of the stellarator power reactor HELIAS / André Häußler ; Betreuer: R. Stieglitz." Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/1219577928/34.
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Ullmann, Til [Verfasser], and Günter [Akademischer Betreuer] Tovar. "The influence of flow shear on drift-wave interactions in the stellarator TJ-K / Til Ullmann ; Betreuer: Günter Tovar." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2021. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-ds-117033.
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Glass, Fenton John, and f. glass@fz-juelich de. "Tomographic Visible Spectroscopy of Plasma Emissivity and Ion Temperatures." The Australian National University. Research School of Physical Sciences and Engineering, 2004. http://thesis.anu.edu.au./public/adt-ANU20051028.002110.
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Extending the use of Doppler spectroscopy as an important plasma diagnostic -- by developing a multi-channel system capable of tomography -- is the foundation of this thesis. A system which can simultaneously measure the emissivity, temperature and flow velocity of plasma ions has been installed, calibrated and operated on the H-1NF heliac, yielding comprehensive and interesting results. The measurements are time-resolved, made from a large range of viewing positions and, using scalar tomographic inversion methods, can be
unfolded to give two-dimensional images of ion emissivity and temperature. The flow velocity profiles, while not inverted, nevertheless lead to a greater understanding of the plasma behaviour.¶
Fifty-five lens-coupled optical fibres, mounted on a large rotatable stainless steel ring, encircle the plasma poloidally and transport light to a multi-channel Fourier-transform spectrometer. This
`coherence-imaging' spectrometer employs an electro-optically modulated birefringent crystal plate to monitor the coherence of an
isolated spectral line. Measurement of the intensity, fringe visibility and phase of the resulting interferogram leads to values
for the emissivity, ion temperature and flow velocity. Using a multi-anode photomultiplier assembly, allows the time-resolved detection of all optical channels simultaneously.¶
The system has been fully calibrated, including a measurement of the spatial response of each line-of-sight. The calibration procedure accounts for the relative channel sensitivities, the response of the line filter and the removal of detector cross-talk. In situ light sources are installed provide routine and accurate relative
intensity calibration of the system.¶
Methods of tomography provide the unfolding of the measured plasma
parameters to construct two-dimensional images of ion temperature and emissivity. Methods of inversion include the iterative ART routine -- using projection data gathered with the light-collecting optics rotated to different viewing positions -- and linear composition of Fourier-Bessel basis functions -- with the data obtained from a
single unrotated viewing position. ART reconstructions of the emissivity are performed without the need for a priori information while those of the ion temperature are computed using regularising functions to help stabilise the
inversion.¶
This new system -- named ToMOSS for Tomographic Modulated Optical
Solid-state Spectrometer -- enables a more detailed study of various plasma
phenomena observed in H-1NF. Among other results, this thesis presents the first tomographic reconstructions of emissivity and temperature fluctuations associated with a large-scale coherent instability.
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Grenfell, Gustavo. "Electromagnetic turbulence in the edge of fusion plasmas: spontaneous and actively modulated features." Doctoral thesis, Università degli studi di Padova, 2020. http://hdl.handle.net/11577/3425800.
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This thesis aims to study the properties of turbulent transport, exploiting the cross-comparison between different magnetic configurations, fusion devices, and plasma regimes. Understanding and controlling cross-field transport in magnetized plasmas devices is a requirement for achieving a commercial fusion reactor. Turbulent transport plays a crucial role in both tokamak and stellarator, while shear flows can impact its growth and development. Such an effect has a beneficial impact on the overall plasma confinement, but it is detrimental for the energy exhaustion since it ultimately decreases the power deposition area on the divertors. The latter phenomenon seems to be, to a large extent, determined by the turbulent coupling between the plasma edge and the scrape-off layer (SOL), governed by travelling turbulent filaments. These structures share some features with the edge-localized mode (ELM) filaments that, in turn, typically result in a large transient heat flux on plasma-facing components. The existence of ELMs in future fusion reactors is a concern since they might reduce the device life-time, while the proper understanding of their characteristics and dynamics can help to control them. The local effective turbulence growth and spreading rate are computed in the TJ-II stellarator from the edge to the SOL with a set of electrostatic sensors. The results show that the local turbulence growth reduces once a shear layer is formed in the plasma edge induced by an external electrode biasing. Besides, the turbulence spreading rate is mainly activated in the SOL, decreasing when the E x B shearing rate becomes comparable to the inverse of the turbulence correlation time, leading to a decoupling of the edge-SOL turbulence. The role of radial electric fields in regulating turbulence propagation is further confirmed in TJ-II by spontaneous neoclassical electron-ion root transition experiments. During this process, the edge radial electric field flips sign continuously from positive to negative values. Through the measurements of two electrostatic probes remotely separated, the zonal flows become amplified during the transition, while turbulence decreases in the ion root phase. Furthermore, the turbulence propagation computed using the transfer entropy technique shows that turbulence propagates radially outward at ~1 km/s during the electron root, reducing substantially in the ion root phase. The electromagnetic properties of turbulent filaments are investigated in RFX-mod operating as tokamak in the single-null configuration.
In this experiment, the edge biasing technique was applied to induce an improved plasma confinement so that a comparison between the L and H-mode regimes is possible. On this purpose, the plasma boundary was monitored with a set of electrostatic and magnetic sensors. Through advanced statistical techniques, filaments are detected and tracked from the edge to the SOL in a two-dimension floating potential map together with their associated plasma density and current density parallel to the equilibrium magnetic field. While in L-mode they travel almost freely, during H-mode their motion becomes restricted to the near SOL. The higher ExB shear in the latter regime is pointed out to be the reason for this effect. Filament dynamics in the two scenarios is discussed in the framework of analytical models and velocity scaling. During L-mode, filaments are better described by the sheath connected regime and the parallel current density and potential structure are shown to be roughly synchronized. In H-mode, however, filaments near the last closed flux surface (LCFS) scale roughly as the inertial regime. In addition, ELM filaments appear spontaneously during the biasing H-mode in RFX-mod. The properties of these structures are compared with the type I ELMs observed in the COMPASS tokamak.Lo scopo di questa tesi è lo studio delle proprietà del trasporto turbolento nella regione di bordo di plasmi fusionistici, sfruttando il confronto incrociato tra diverse configurazioni magnetiche, diverse macchine di fusione e diversi regimi del plasma. La comprensione dei meccanismi che regolano il trasporto e il loro controllo costituiscono un tassello essenziale per il raggiungimento dell’obiettivo di un reattore a fusione commerciale. Il trasporto turbolento svolge un ruolo cruciale sia nella configurazione tokamak sia nello stellarator, d’altro canto lo sviluppo di gradienti di velocità nella regione esterna del plasma può influenzarne e controllarne l’insorgenza e la crescita. Un tal effetto ha un impatto benefico sul confinamento globale del plasma, tuttavia presenta delle controindicazioni per quanto riguarda lo smaltimento dell’energia proveniente dal plasma, in quanto questa si concentra in un’area ridotta delle piastre dei divertori. Quest'ultimo fenomeno sembra essere in larga misura determinato dall'accoppiamento turbolento tra il bordo del plasma e lo 'scrape-off layer' (SOL) (all'esterno dell’ultima superficie chiusa - LCFS acronimo in inglese), governato da filamenti turbolenti. Queste strutture condividono alcune caratteristiche con i filamenti che si manifestano durante ELM (edge-localized mode/modi localizzati nella regione di bordo) che, a loro volta, generano un grande flusso di calore transitorio sui componenti esposti al plasma. L'esistenza di ELM nei futuri reattori a fusione costituisce una notevole sfida tecnologica attualmente perché può ridurre la durata del dispositivo mentre la corretta comprensione delle sue caratteristiche e dinamiche può aiutare a controllarli. In questo lavoro di tesi la crescita della turbolenza locale e il tasso della sua dispersione radiale sono calcolati nello stellarator TJ-II dal bordo allo SOL con un sistema di sensori elettrostatici. I risultati mostrano che la crescita della turbolenza locale si riduce quando si forma un forte gradiente di velocità nel bordo del plasma indotto da un elettrodo esterno polarizzato. I risultati dimostrano che il tasso della dispersione della turbolenza agisce principalmente nel SOL, diminuendo quando gradiente di velocità E x B diventa paragonabile all'inverso del tempo di correlazione della turbolenza, portando a un disaccoppiamento della turbolenza edge-SOL. Il ruolo dei campi elettrici radiali nella regolazione della propagazione della turbolenza è ulteriormente confermato nell’esperimento TJ-II, mediante esperimenti di transizione spontanea electron-ion root. Durante questo processo, il campo elettrico radiale indotto al bordo cambia da valori positivi a negativi. Attraverso le misurazioni di due sonde elettrostatiche posizionate in due regioni lontane tra loro, si osserva che le regioni caratterizzate da velocità omogenea (zonal flows) vengono amplificati durante la transizione, mentre la turbolenza diminuisce nella fase di campo elettrico negativo (ion root). Inoltre, la propagazione della turbolenza calcolata usando la tecnica di trasferimento dell’entropia mostra che la turbolenza si propaga radialmente verso l'esterno a ~1 km/s durante la fase di campo elettrico positivo (electron root), riducendosi sostanzialmente nella fase della ion root. Altro importante argomento trattato in questo levoro di tesi riguarda le proprietà elettromagnetiche dei filamenti turbolenti. Queste strutture sono state studiate in dettaglio nell’esperimento RFX-mod operato in configurazione tokamak con un punto a X nella separatrice (single-null). Anche in questo esperimento, è stata applicata la tecnica di polarizzazione del bordo per indurre un miglioramento del confinamento del plasma in modo che sia possibile un confronto tra i regimi L e H-mode. A tal fine, il bordo del plasma è stato monitorato con una serie di sensori elettrostatici e magnetici. Utilizzando tecniche statistiche avanzate, i filamenti vengono rilevati e tracciati dal bordo verso il SOL in una mappa di potenziale flottante bidimensionale insieme alla densità del plasma e alla densità di corrente parallela al campo magnetico di equilibrio. Mentre nella modalità L-mode i filamenti viaggiano quasi liberamente, durante la modalità H-mode il loro movimento è limitato al SOL nella regione prossima all’ultima superficie chiusa (near SOL). Il gradiente di velocità ExB più elevato in quest'ultimo regime sembra essere la ragione di questo effetto. Le dinamiche del filamento nei due scenari sono discusse nell'ambito di modelli analitici e di scale di velocità e dimensione dei filamenti stessi. Durante la modalità L-mode, i filamenti sono meglio descritti dal regime che prevede i filamenti connessi allo strato di Debye nelle superfici esposte al plasma, in questo caso si è osservato che la densità di corrente parallela e la struttura potenziale viaggiano approssimativamente sincronizzati. In modo H, tuttavia, i filamenti vicino alla LCFS sono meglio descritti dal regime inerziale. I filamenti ELM compaiono spontaneamente durante la polarizzazione del modo H in RFX-mod. Parte dello studio è stato quindi dedicato alla loro caratterizzazione. Queste strutture sono state confrontate con gli ELM di tipo I osservati nel tokamak COMPASS. In entrambi i dispositivi, i filamenti ELM trasportano una sostanziale corrente verso il SOL. L'analisi statistica rivela una struttura fine complessa e ricca all'interno dei cicli ELM. I filamenti ELM sono espulsi nel SOL verso la parete in corrispondenza di una riduzione dei gradienti radiali medi e di una più intensa fluttuazione del campo magnetico perpendicolare. Infine l’esistenza di una fase di modi quasi coerenti prima del verificarsi degli eventi di ELM è stata caratteristica comune in entrambi i dispositivi.
14
Henkel, Marion [Verfasser]. "Measurements of ion temperatures and fast particles in the scrape-off layer of W7-X stellarator and EAST tokamak / Marion Henkel." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2021. http://d-nb.info/1239413556/34.
Full text
15
Ciaccio, Giovanni. "Flow and transport in the edge of fusion devices." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423733.
Full textAbstract:
The main topic of the Thesis is the study of the electrostatic, plasma
response (Er and flows) to magnetic islands embedded in the chaotic edge of
a tokamak, when resonant magnetic perturbations (RMPs) are applied. Results
are compared with the known phenomenology and theory in the chaotic
edge of a reversed-field pinch (RFP). Proxies of the two configurations are
the tokamak TEXTOR, with the application of the dynamic ergodic divertor
(DED); and the RFX-mod RFP. The main tool used for simulations of
islands, two-fluid transport (electrons and ions), and ambipolar Er field, is
the Hamiltonian guiding-center code Orbit.
As an initial step, to validate the reconstruction of the edge topology of
TEXTOR and RFX, the Orbit code has been validated against the volumepreserving
code Nemato [24]. In the limit of low energy, Orbit can be used
to trace the magnetic field topology, in a way in all respects similar to field
line-tracing codes. Nemato is a field-line tracing code, implemented to integrate
solenoidal flows for incompressible fluid dynamics, with automatic
volume preservation [47]. The question is, how accurate is the description of
the magnetic field with Orbit, given that it is a Hamiltonian code (therefore,
with a simplectic matrix), but it uses a Runge-Kutta (RK) integrator
instead of a fully implicit solver (which is the case of Nemato). Besides
this, Orbit describes perturbations in terms of a scalar field , such that
~B = r × ~B0, with B0 the equilibrium field. The two codes are validated
on the structure of the q = 0 island chain, which characterizes the
multi helicity (MH) configuration in RFP. As input for both codes we use
the snapshot of a cylindrical 3D nonlinear, magnetohydrodynamic (MHD)
visco-resistive simulation (SpeCyl code [20]). The first benchmarking test
employs a Hamiltonian (single-mode) magnetic field configuration. Both
codes successfully yield field lines which follow flux surfaces in both the
m = 1 and m = 0 cases. The comparison between the codes is then extended
to a chaotic magnetic field configuration, by including many modes.
The result is that the scalar field representation of Orbit and the RK integrator
do not include measurable differences in the Poincar´e maps and in
the calculation of the correlation length of the chaotic field.
As a second step in this Thesis, in order to develop a common picture of
particle transport with edge magnetic islands in Tokamaks and RFPs, test
particle transport simulations are carried out in TEXTOR following the
steps of the study performed in RFX-mod [123]. The RMP configurations
studied are the m/n = 12/4 and 3/1. The Orbit code has been adapted to
the equilibrium of TEXTOR (circular equilibrium with pressure [144]), and
a proper form for the eigenfunctions has been developed, on the basis of the
analytical formula used in TEXTOR using as input the current flowing in
the DED. The resulting Poincar´e plots show the well-known, basic features
of TEXTOR stochastic edge, such as the inner island chain, the remnant
islands, and the laminar flux tubes embedded in the ergodic fingers, which is
consistent with previous works on this subject. Maps in the (r, ) plane of the
electron and ion parallel connection length to the wall, Lk(r, ), highlight the
properties of the magnetic structures observed in the Poincar´e plot: while
ions, having a large Larmor radius, are weakly affected by the magnetic
topology, electron trajectories are linked to the magnetic field lines. The
behavior of Lk entails a characteristic modulation of the radial electric field
Er with large positive values in the zone with electron Lk 0 (the so-called
laminar flux tubes, which occupy a region in between the main island chain
and the remnant islands).
As a further step, the evaluation of the local radial transport of particles,
i.e. ion and electron diffusion coefficients (Di and De, respectively),
has been performed along a helical path from the O-point (OP) through the
X-point (XP) of an m/n = 4/1 remnant island. The result shows that Di
is rather constant along the path, and it is almost neoclassical, while De is
larger (4 ÷ 40 m2/s), and is strongly modulated (larger at the XP, lower at
the OP), consistently with the Lk maps. Finally, an analytic 3D formulation
of the ambipolar potential for the 3/1 DED configuration is developed on
the basis of the geometry of the m/n = 4/1 magnetic island, that balances
electron and ion fluxes inside the island. The result is compared to measurements
of plasma potential inside an m/n = 4/1 island in the edge of the
TEXTOR device and with the analysis on RFX-mod edge. In RFX-mod
Orbit predicts the potential well to stay in proximity of the OP of the
main island (m/n = 0/1), while measurements show the potential well near
the XP. In the TEXTOR experiment fast Mirnov probe measurements show
that the potential well corresponds to the XP of the m/n = 4/1 island, i.e.
the region with larger De, consistently with Orbit results. The difference
between RFX and TEXTOR could be ascribed to a collisional dependence
(the case of RFX is highly collisional, contrary to TEXTOR); to a different
level of chaos, in RFX compared to TEXTOR; or to a more pronounced
plasma-wall interaction.
The final, main message of the Thesis is that RMPs in tokamaks, even if
induced as static perturbation, are capable of producing a pattern of large,
radial electric field Er, which is the footprint of the underlying topology. The
pattern of Er can be successfully reproduced by Orbit. The comparison
with RFX shows that collisional effects can be important in determining
amplitude and phase of this electrostatic potential.L’argomento principale della Tesi `e lo studio delle isole magnetiche, al bordo di una macchina tokamak, create per mezzo di perturbazioni magnetiche risonanti (RMP), e della relativa risposta elettrostatica del plasma (flussi e campo elettrico radiale Er). I risultati sono stati confrontati con la fenomenologia e la teoria gi`a conosciute nell’ambito del chaos magnetico al bordo di una macchina con configurazione magnetica reversed-field pinch (RFP). In particolare, l’analisi `e stata eseguita sul tokamak TEXTOR ed il confronto fatto con il RFP RFX-mod. Per tale studio, si ´e utilizzato il codice hamiltoniano di centro guida Orbit, che permette di eseguire simulazioni di trasporto di particelle e ricostruire la topologia magnetica. In primis, Orbit ´e stato confrontato con il codice volume-preserving Nemato [24], allo scopo di validare la ricostruzione della topologia magnetica di Orbit, al bordo di TEXTOR e RFX-mod. Nel limite di bassa energia, Orbit pu`o essere utilizzato per tracciare le linee di campo magnetico, in modo simile ai codici field-line tracing, come Nemato. Nemato integra flussi solenoidali per fluidi incomprimibili, conservando automaticamente il volume [47]. Si vuole verificare quanto accurata sia la descrizione di un campo magnetico da parte di Orbit, che pur essendo un codice hamiltoniano, usa un integratore Runge-Kutta (RK) anzich´e risolvere in modo completamente implicito le equazioni del moto (come fa Nemato). Inoltre, in Orbit le perturbazioni sono descritte mediante un campo scalare , cos`ı che ~B = r × ~B0, dove B0 `e il campo all’equilibrio. I due codici sono validati su una struttura composta da isole q = 0 che caratterizzano la configurazione multy helicity (MH) nel RFP. I dati in ingresso, per entrambi i codici, provengono da una simulazione MHD, visco-resistive in geometria cilindrica 3D non lineare, del codice SpeCyl [20]. Inizialmente il confronto `e stato eseguito su una semplice configurazione con uno solo modo non nullo nello spettro delle perturbazioni, verificando che entrambi i codici creano linee di campo che seguono le superfici di flusso calcolate analiticamente. Il confronto `e quindi esteso alla configurazioni caotica (con tutti i modi). Il risultato `e che la rappresenzione di Orbit e l’integratore RK, non comportano alcuna differenza apprezzabile nelle mappe di Poincar´e e nel calcolo della lunghezza di correlazione. Nella seconda parte della Tesi, allo scopo di disegnare un quadro coix mune del trasporto di particelle nel tokamak RMP e nel RFP, simulazioni di trasporto di particelle (ioni ed elettroni) sono state eseguite, seguendo le analisi storicamente effettuate in RFX-mod [123]. In particolare, due configurazioni magnetiche in TEXTOR sono state considerate: m/n = 12/4 e 3/1. Il codice Orbit `e stato adattato ricostruendo l’equilibrio magnetico di TEXTOR (equilibrio circulare con pressione [144]) e le perturbazioni, sulla base di una formula analitica sviluppata a TEXTOR. Le mappe di Poincar´e create con Orbit mostrano le caratteristiche base del bordo caotico di TEXTOR, come la catena interna di isole, le isole remnant, ed i tubi di flusso laminare circondati da una zona ergodica (ergodic fingers), consistentemente con lavori precedenti effettuati a TEXTOR. Le propriet`a delle suddette strutture sono evidenziate con simulazioni di lunghezza di connessione, Lk(r, ): mentre gli ioni, avendo un raggio di Larmor pi`u grande, sono debolmente influenzati dalla topologia magnetica, le traiettorie degli elettroni sono vincolate alle linee di campo. L’andamento di Lk comporta una caratteristica modulazione di Er con valori positivi nelle zone con Lk 0 (cio`e i tubi di flusso laminare tra le isole remnant e le catena di isole interna). Successivamente, i coefficienti di diffusione ionici ed elettronici (Di and De, rispettivamente), sono stati calcolati lungo l’intervallo poloidale tra l’Opoint (OP) e l’X-point (XP) dell’isola remnant m/n = 4/1, per valutare localmente il trasporto radiale di particelle. Il risultato mostra che Di `e circa costante lungo l’intervallo e quasi neoclassico, mentre De `e pi`u grande (4 ÷ 40 m2/s), e fortemente modulato (pi`u grande nel XP, pi`u piccolo nel OP), consistentemente con le mappe di Lk. Infine, una formulazioni 3D, analitica del campo ambipolare nella configurazione 3/1 `e stata sviluppata a partire dalla geometria dell’isola m/n = 4/1, che bilancia i flussi ionici ed elettronici al bordo. Il risultato `e confrontato con misure di potenziale di plasma nell’isola m/n = 4/1 e con le analisi al bordo di RFX-mod. In RFXmod Orbit predice una buca di potenziale in prossimit`a del OP dell’isola principale (m/n = 0/1), mentre le misure mostrano che la buca sia vicino al XP. In TEXTOR le misure mostrano che la buca di potenziale in corrispondenza del XP dell’isola m/n = 4/1, cio`e la regione con grande De, consistentemente con i risultati di Orbit. La differenza tra RFX e TEXTOR pu`o essere dovuta alla dipendenza dalle collisioni (in RFX si ha alta collisionalit`a, contrariamente a TEXTOR); a una diversa quantit`a di caos tra RFX-mod e TEXTOR; oppure ad una interazione plasma-parete pi`u pronunciata in RFX-mod. Il messaggio principale delle Tesi `e che gli RMPs nei tokamak, anche se indotti come perturbazioni statiche, sono capaci di produrre un campo elettrico radiale Er, la cui struttura `e la stessa della topologia magnetica al bordo. Tale struttura pu`o essere riprodotta in ottima approssimazione da Orbit. Il confronto con RFX dimostra che gli effetti collisionali possono essere importanti nel determinare ampiezza e fase di questo potenziale elettrostatico.
16
García, Olaya Jerónimo. "Study of electron heat transport in LHD and TJ-II." Doctoral thesis, Universitat Politècnica de Catalunya, 2006. http://hdl.handle.net/10803/6609.
Full textAbstract:
The magnetically confined plasmas study is one of the most promising research fields in the present days due to the high perspectives of unlimited and clean energy that fusion has generated. In this framework, the stellarator devices play a significant role because of, unlike in the tokamak case, their continuum working regime, which will be an essential feature of the future fusion commercial reactor.Heat transport studies in stellarator devices are completely necessary since the main plasma properties (and therefore, the total fusion power generated) are absolutely dependent. Nowadays, the largest stellarator in the world is the Large Helical Device (LHD). There is also a stellarator device is Spain, TJ-II, which is located in the installations of CIEMAT in Madrid. In this thesis, turbulent and conductive heat transport is studied in both devices with the aim of comparing its formation and suppression.
First of all, collisional transport, i.e. neoclassical transport, which is caused by the particle collisions, is studied by means of a new transport model implemented in the transport code PRETOR-Stellarator. This model is able to calculate heat diffusivities as well as the neoclassical electric field with reasonable accuracy without spending as much computational time as in the Monte Carlo techniques. It is deduced from the results that, for both TJ-II and LHD, neoclassical transport may be quite important in plasmas with low density and high temperatures, although higher levels of neoclassical transport are obtained in TJ-II. Both devices share the feature that in low collisional plasmas, a high positive neoclassical electric field with a high shear appears in the plasma core. This electric field can be responsible of the suppression of the turbulence heat transport.
Some new turbulent heat transport models have been added to PRETOR-Stellarator in order to study this kind of transport. Both, LHD and TJ-II, share a common heat transport in the confinement region (plasma core), called drift wave electromagnetic transport, and which is due to the fluctuations of the magnetic field. Outside this region, turbulent heat transport in LHD has similar characteristic to that in tokamaks, whereas in TJ-II, turbulent transport is maintained.
Turbulent heat transport reduction is a major issue in fusion research, since the capability of producing commercial fusion energy depends strongly on the low levels of turbulence of the plasma. The appearance of a neoclassical electric field in the plasma core and its interaction with turbulent transport has been studied. It is shown that this electric field is able to generate a rotation in the plasma which is able to suppress turbulent transport to neoclassical levels when density is low enough. These plasmas are called to have an internal transport barrier and have stepped electron temperature profiles with hollow electron density profiles.
Another important phenomenon related with electron heat transport is non-local transport, which can not be studied within the general diffusive framework that is used to study turbulent transport in plasmas. The non-local transport is caused by the interaction of long distant parts of the plasma. In this thesis, a new model for this type of transport, which is based on the convolution over a kernel of the neoclassical transport, has been proposed to explain this phenomenon. It has been shown that this model is able to simulate the main characteristics of this transport, e.g. fast pulses propagation, ballistic transport or the growing of the turbulence levels close to the axis of the device. All these phenomena have been observed in LHD and TJ-II.
Finally, once electron heat transport in stellarators has been clarified, a comparison of the designs of the future commercial reactor based on both, stellarators and tokamaks, has been carried out. A stellarator commercial reactor, based on the design of the LHD, would have a 15.5 m major radius, 2.5 m minor radius, with a continuum working regime based on low temperatures and high densities. Main energy sinks are due to conductive-convective heat losses and radiation losses (in a 95% from Bremmstrahlung radiation). The fact that it has such a large major radius makes this design expensive and difficult to build. A tokamak fusion reactor would be smaller, however, the high temperatures achieved make cyclotron radiation losses to be very high, and a wall with a high reflection coefficient seems to be necessary.
L'estudi de les propietats dels plasmes confinats magnèticament esta esdevenint un dels temes primordials de recerca degut a les prometedores perspectives (de netedat i ampli abast) que l'energia produïda per fusió nuclear està fomentant. Es dins d'aquest context on l'estudi dels dispositius de confinament magnètic de tipus stellarator juguen un paper molt important, ja que un reactor de fusió basat en aquest concepte podria tenir (al contrari dels tokamaks) un mode de funcionament continu i no polsat.
L'estudi del transport de calor en el dispositius de fusió per confinament magnètic de tipus stellarator és totalment necessari, ja que les propietats del plasma (i per tant de l'energia produïda per fusió) en depenen completament. Actualment, el stellarator més gran del món es troba al Japó i es diu Large Helical Device (LHD), mentre que a Espanya, el stellarator TJ-II es troba a les instal·lacions del CIEMAT a Madrid. En aquesta tesi, s'estudien ambdós dispositius per tal de determinar de que depèn que aparegui o que desaparegui el transport de calor turbulent en aquests dispositius, i si hi ha algun tipus de punt en comú.
En primer lloc, s'analitza el transport de calor colisional (degut a la col·lisió de les partícules que formen el plasma) mitjançant la introducció d'un model de transport colisional (anomenat neoclàssic) al codi de transport PRETOR-Stellarator. Aquest model es capaç de calcular magnituds físiques tal com difusivitats i camps elèctrics neoclàssics però sense consumir tant de temps com a d'altres tècniques que utilitzen mètodes de Monte Carlo. Dels resultats es desprèn que el transport neoclàssic, tant al TJ-II com al LHD, pot ser important, en plasmes amb baixa densitat i temperatures grans. Ambdós dispositius comparteixen la característica de que apareix, en aquests casos, un gran camp elèctric al centre del plasma que pot ser fa que el transport turbulent disminueixi.
Mitjançant la introducció de diferents models pel transport turbulent a PRETOR-Stellarator, s'estudia el transport turbulent als dos dispositius. De l'anàlisi es dedueix que ambdós dispositius poden compartir el mateix tipus de transport (anomenat electromagnètic) i que es degut a les variacions locals del camp magnètic. Tanmateix, fora de la zona central, el LHD té un tipus de transport semblant al que existeix al tokamak JET (Joint European Torus), mentre que el TJ-II continua amb el transport electromagnètic.
La reducció del transport turbulent prèviament estudiat és un tema capdal ja que permetria un millor confinament del plasma. S'ha estudiat com el camp elèctric format al centre del plasma pot generar un rotació que disminueix el transport turbulent tant al LHD com al TJ-II. Aquests plasmes es diuen que tenen una barrera interna del transport que redueix el transport turbulent a valors neoclàssics sempre que la densitat sigui prou baixa.
Un altre fenomen lligat al transport molt important és el transport no local, que es degut a les correlacions entre parts llunyanes del plasma i que no es pot entendre dintre del context del transport difusió que se sol emprar per a estudiar el plasmes confinats. En el marc d'aquesta tesi s'ha dissenyat un model de transport no local per mitjà d'una convolució sobre el transport neoclàssic. Amb aquest model s'ha aconseguit reproduir molts del efectes no locals que apareixen als plasmes (com ara la ràpida propagació de fenòmens turbulents o la propagació de fronts turbulents que mantenen una forma d'ona ), i que s'han descrit tant al LHD com al TJ-II.
Finalment es realitza una comparació entre els dissenys dels reactors de fusió basats en stellarators i tokamaks. Un reactor de fusió stellarator tindria un radi major de 15.5 m i treballaria en mode continu amb alta densitat i baixa temperatura. Les pèrdues d'energia més importants serien, en aquest cas, degudes a la convenció i conducció dins del plasma. El fet que tingui una grandària tan gran el faria molt car de construir. En el cas dels tokamaks, la seva grandària seria més petita, però les pèrdues per radiació ciclotró serien molt grans (degut al règim d'alta temperatura i baixa densitat) i el disseny d'una paret del reactor amb un coeficient de reflexió molt gran fora totalment necessari.
17
Fontanet, Saez Joan. "Simulación de plasmas de dispositivos de fusión por confinamiento magnético tipo tokamak y stellarator. Validación experimental y aplicación al estudio del Heliac Flexible TJ-II." Doctoral thesis, Universitat Politècnica de Catalunya, 2001. http://hdl.handle.net/10803/6598.
Full textAbstract:
En el estudio de la fusión por confinamiento magnético es crucial conocer con detalle las condiciones físicas del plasma confinado. En este sentido los códigos de simulación son una herramienta muy útil para interpretar las propiedades del plasma. A lo largo de esta tesis se ha estudiado las propiedades del plasma de tokamaks y stellarators y se ha contribuido al desarrollo del código de transporte PRETOR, creado en el JET. Estos estudios se han realizado dentro de la colaboración existente entre el DFEN de la UPC y el Laboratorio Nacional de Fusión del CIEMAT.El código PRETOR permite simular la variación radial y la evolución temporal de las principales magnitudes físicas de un plasma de fusión. Para valorar la bondad de los modelos implementados en el código y determinar la corrección de sus resultados los resultados de la simulación de las magnitudes más relevantes de diversas descargas se comparan con los datos experimentales. De esta comparación se deduce que las magnitudes simuladas presentan un buen acuerdo con los datos experimentales aunque debe destacarse que los errores experimentales son bastante grandes y no siempre están disponibles.
En el desarrollo de esta tesis también se ha aplicado el código PRETOR para el estudio de la parada de emergencia de ITER-DDR, con 1500 MW de potencia de fusión funcionando en un estado estacionario en ignición. Se ha estudiado con detalle la evolución del plasma durante una parada implementada mediante la interrupción del suministro de combustible. Este método se muestra efectivo para reducir la potencia de fusión en unas decenas de segundos evitando una disrupción del plasma en todo el escenario.
Se han realizado diversas modificaciones en el código para hacerlo más versátil y adaptarlo a las necesidades específicas que han ido surgiendo. La modificación más destacada es la incorporación a PRETOR de una rutina más elaborada que la inicialmente implementada en el código para el cálculo de la deposición de potencia adicional por inyección de haces neutros.
En los últimos años la investigación de stellarators ha adquirido una creciente importancia debido a las ventajas que presentan este tipo de dispositivos. Además hay que destacar que el programa de fusión por confinamiento magnético español se centra en el Heliac Flexible TJ-II de la asociación EURATOM-CIEMAT. Por estos motivos y para disponer de un código que sea capaz de simular descargas de stellarators, PRETOR ha sido modificado de forma substancial para crear la versión PRETOR-Stellarator. Esta modificación del código presenta un aspecto inédito de la tesis en el ámbito internacional.
Los módulos que han sido adaptados afectan a la configuración magnética, al transporte de energía y partículas y a la geometría del plasma. Una vez modificado el código, éste se ha aplicado al análisis del plasma de Heliac Flexible TJ-II. El objetivo de este estudio es comprobar que las modificaciones introducidas en PRETOR permiten simular correctamente descargas de stellarators. Los resultados obtenidos con PRETOR se comparan con los obtenidos con el código PROCTR, un código utilizado en el CIEMAT para el estudio del TJ-II y de otros stellarators.
Los resultados demuestran que los perfiles de temperatura se reproducen correctamente, estos resultados son similares a los obtenidos con PROCTR. Los valores experimentales de la potencia radiada y de la energía almacenada en el plasma han sido satisfactoriamente predichos mediante la simulación de PRETOR-Stellarator.
El camino abierto por esta tesis permitirá ahondar en el estudio del plasma del heliac flexible TJ-II, el código está disponible para utilizarse en este dispositivo e incorporar nuevas modificaciones para adaptarlo a las necesidades que vayan apareciendo.
In the study of the fusion by magnetic confinement it is crucial to know the physical behaviour of the confined plasma with detail. In this sense the simulation codes are a very useful tool to analyse the properties of the plasma. Throughout this thesis the properties of the plasma of tokamaks and stellarators has been studied and the transport code PRETOR, created in the JET, has been developed. These studies have been developed within the existing collaboration between the DFEN in the UPC and the Laboratorio Nacional de Fusión of the CIEMAT.
The PRETOR code allows the simulation of the radial variation and the temporal evolution of the main physical magnitudes of a fusion plasma. The results of the simulation of the most important magnitudes of diverse shots are compared with the experimental data in order to evaluate the goodness of the models implemented in the code and to determine the correction of their results. From this comparison it's deduced that the simulated magnitudes present a good agreement with the experimental data although it must be stand out that the experimental errors are quite large and they not always are available.
In the development of this thesis the code PRETOR has also been applied to the study of the shutdown emergency of ITER-DDR, with 1500 MW of fusion power operating in an ignition stationary state. The evolution of the plasma has studied with detail during the shutdown implemented by means of the interruption of the fuel injection. This method is effective to reduce the fusion power in tens of seconds avoiding a plasma disrupción in all the scenarios.
Several modifications have been made in the code in order to make it more versatile and to adapt it to the specific arisen necessities. The most outstanding modification is the incorporation to PRETOR of more complex routine than that initially implemented in the code for the calculation of the additional power deposition by neutral beam injection.
In the last years the investigation of stellarators has acquired an increasing importance due to the advantages that this type of devices presents. Besides it is necessary to emphasise that the Spanish program of fusion by magnetic confinement is focused in Flexible Heliac TJ-II in the asociación EURATOM-CIEMAT. For these reasons and in order to have a code able to simulate stellarators shots, PRETOR has been modified of substantial form to create the PRETOR-Stellarator version. This modification of the code presents an new aspect of the thesis in the international scope.
The modules that have been adapted affect to the magnetic configuration, the transport of energy and particles and to the plasma geometry. Once the code has been modified, it has been applied to the analysis of TJ-II Flexible Heliac plasmas. The objective of this study is to verify that the modifications introduced in PRETOR allow to simulate correctly stellarators discharges. The results obtained with PRETOR are compared with that ones obtained with PROCTR code, a code used in the CIEMAT for the study of the TJ-II and others stellarators.
The results demonstrate that the temperature profiles are reproduced correctly, these results are similar to the obtained ones with PROCTR. The experimental values of the radiated power and the stored energy in the plasma have been predicted satisfactorily by means of the simulation with PRETOR-Stellarator.
The way open by this thesis will allow studying in depth the plasma of TJ-II flexible heliac, the code is available to be used in this device and to incorporate new modifications to adapt it to the necessities that will appear.
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Pinzón, Acosta Javier Rodrigo [Verfasser], Ulrich [Akademischer Betreuer] Stroth, Raul [Akademischer Betreuer] Sanchez, Raul [Gutachter] Sanchez, Gonzalo Luis [Gutachter] Garcia, Ulrich [Gutachter] Stroth, and Lothar [Gutachter] Oberauer. "Modelling and Application of Doppler Reflectometry for Advanced Turbulence Studies on the ASDEX Upgrade Tokamak and the TJ-II Stellarator : Modellierung und Anwendung von Doppler-Reflektometrie für erweiterte Studien der Turbulenz am Tokamak ASDEX Upgrade und am Stellarator TJ-II / Javier Rodrigo Pinzón Acosta ; Gutachter: Raul Sanchez, Luis Garcia Gonzalo, Ulrich Stroth, Lothar Oberauer ; Ulrich Stroth, Raul Sanchez." München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1165227509/34.
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Stange, Torsten [Verfasser], Heinrich Peter [Akademischer Betreuer] Laqua, Dieter [Akademischer Betreuer] Breitschwerdt, and Robert [Akademischer Betreuer] Wolf. "Microwave heating and diagnostic of suprathermal electrons in an overdense stellarator plasma / Torsten Stange. Gutachter: Dieter Breitschwerdt ; Robert Wolf ; Heinrich Peter Laqua. Betreuer: Heinrich Peter Laqua." Berlin : Technische Universität Berlin, 2014. http://d-nb.info/1067385762/34.
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Sallander, Eva. "Magnetohydrodynamic spectroscopy of magnetically confined plasmas." Doctoral thesis, Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3139.
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Garland, Stephen [Verfasser], and Thomas [Akademischer Betreuer] Hirth. "Investigation into the influence of magnetic field structure on the dynamical and spatial properties of plasma edge turbulence in the stellarator TJ-K / Stephen Garland ; Betreuer: Thomas Hirth." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/1195529457/34.
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Fontdecaba, Climent Josep Maria. "Estudio del transporte de energía en plasma de fusión termonuclear con medidas experimentales obtenidas del espectrometro de intercambio de carga, realizado mediante técnicas de participación remota." Doctoral thesis, Universitat Politècnica de Catalunya, 2004. http://hdl.handle.net/10803/6600.
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En la investigació de la fusió termonuclear controlada per confinament magnètic es important conèixer el transport d'energia en els plasmes, doncs aquest transport és el que fa que es refredi més o menys ràpidament amb el que s'obtindran o no les reaccions de fusió. El transport d'energia en els plasmes es majoritàriament turbulent o anòmal, fins la data no hi ha una teoria que expliqui satisfactòriament aquest tipus de transport, por tant per poder realitzar estudis i extrapolacions s'utilitzen models semiempírics en codis de simulació validats. Un d'aquests codis de simulació és PRETOR-Stellarator, utilitzat i millorat durant la realització d'aquesta tesi.Per altra banda un aspecte important dels dispositius de fusió son els diagnòstics, eines imprescindibles per comprendre les propietats del plasma confinat al seu interior. Un dels diagnòstics instal·lats en el stellarator heliac flexible TJ-II del "Laboratorio Nacional de Fusión" de Madrid és l'espectròmetre d'intercanvi de càrrega. Durant aquesta tesi s'ha aprofundit en el seu estudio per després poder analitzar els seus resultats.
Amb la següent generació de màquines de fusió és pretén augmentar les prestacions i arribar a demostrar la viabilitat d'aquesta tecnologia per produir electricitat. Per això les màquines han de ser molt més grans i, per tant, més cares i complexes. Por això diversos països han col·laborat en el disseny i, en el futur, construcció del dispositiu. Per a que els científics de tots els països participants puguin beneficiar-se de les dades obtingudes per les noves màquines es fan imprescindibles les eines de participació remota. Un dels punts principals d'aquesta tesi és la utilització d'aquest tipus d'eines pel funcionament de l'espectròmetre d'intercanvi de càrrega.
En aquesta tesi s'han realitzat diferents estudis de transport de la calor pels electrons en el plasma. Primer s'ha acabat de validar el codi PRETOR-Stellarator amb dades de descàrreges de TJ-II obtingudes mitjançant la participació remota. Seguidament s'ha introduït una modificació del codi que permet simular amb més exactitud la part central del plasma, amb aquestes modificacions s'ha realitzat un estudi del mode de confinamient millorat de TJ-II.
Amb l'espectròmetre d'intercanvi de càrrega s'han realitzat una sèrie de mesures destinades a comprovar les asimetries poloidals de fuga de ions del plasma i després s'ha intentat ver la influència de la inducció de corrent en el plasma en la temperatura dels ions.
Finalment amb dades obtingudes de l'espectròmetre d'intercanvi de càrrega s'ha realitzat un estudi del transport del calor pels ions. Primer s'ha realitzat fins un radi efectiu de 0.6 aproximadament i després, gràcies a una millora del diagnòstic, s'ha pogut completar el perfil radial fins fora de l'última superfície de flux tancada. Això és una novetat, ja que fins ara no s'havia fet, a més com a resultat dóna una temperatura dels ions totalment plana al llarg de tot el radi i fins i tot fora d'aquesta última superfície tancada de flux.
Amb aquesta tesi s'han provat eines de participació remota comprovant que són aptes per la seva utilització en grans instal·lacions científiques. A més s'ha aprofundit el coneixement dels plasmes de TJ-II. També s'ha acabat de validar el codi PRETOR-Stellarator, amb el que es té una eina útil per la simulació de plasmes de fusió.
En la investigación de la fusión termonuclear controlada por confinamiento magnético es importante conocer el transporte de energía en los plasmas, pues este transporte es el que hace que se enfríe más o menos rápidamente con lo que se obtendrán o no las reacciones de fusión. El transporte de energía en los plasmas es mayoritariamente turbulento o anómalo, hasta la fecha no hay una teoría que explique satisfactoriamente este tipo de transporte, por tanto para poder realizar estudios y extrapolaciones se utilizan modelos semiempíricos en códigos de simulación validados. Uno de estos códigos de simulación está PRETOR-Stellarator, utilizado y mejorado durante la realización de esta tesis.
Por otra parte un aspecto importante de los dispositivos de fusión son los diagnósticos, herramientas imprescindibles para comprender la propiedades del plasma confinado en su interior. Uno de los diagnósticos instalados en el stellarator heliac flexible TJ-II del Laboratorio Nacional de Fusión de Madrid es el espectrómetro de intercambio de carga. Durante esta tesis se ha profundizado en su estudio y manejo para después poder analizar sus resultados.
Con la siguiente generación de máquinas de fusión se pretende aumentar las prestaciones y llegar a demostrar la viabilidad de esta tecnología para producir electricidad. Para ello la máquinas deben ser mucho mayores y, por tanto, más caras y complejas. Por esto diversos países han colaborado en el diseño y, en el futuro, construcción del dispositivo. Para que los científicos de todos los países participantes puedan beneficiarse de los datos obtenidos por la nuevas máquinas se hacen imprescindibles las herramientas de participación remota. Uno de los puntos principales de esta tesis es la utilización de este tipo de herramientas para el manejo del espectrómetro de intercambio de carga, con lo que es un ejemplo para el futuro.
En esta tesis se han realizado diferentes estudios de transporte de calor por los electrones en el plasma. Primero se ha acabado de validar el código PRETOR-Stellarator con datos de descargas de TJ-II obtenidos mediante la participación remota. Seguidamente se ha introducido una modificación del código que permite simular con mayor exactitud la parte central del plasma, con estas modificaciones se ha realizado un estudio del modo de confinamiento mejorado de TJ-II.
Con el espectrómetro de intercambio de carga se han realizado una serie de medidas destinadas a comprobar las asimetrías poloidales de fuga de iones del plasma y después se ha intentado ver la influencia de la inducción de corriente en el plasma en la temperatura de los iones.
Finalmente con datos obtenidos del espectrómetro de intercambio de carga se ha realizado un estudio del transporte del calor por los iones. Primero se ha realizado hasta un radio efectivo de 0.6 aproximadamente y después, gracias a una mejora del diagnóstico, se ha podido completar el perfil radial hasta fuera de la última superficie de flujo cerrada. Esto último es una novedad, ya que hasta ahora no se había hecho, además da como resultado una temperatura de los iones totalmente plana a lo largo de todo el radio e incluso fuera de esta última superficie cerrada de flujo.
Con esta tesis se han probado herramientas de participación remota comprobando que son aptas para su empleo en grandes instalaciones científicas. Además se ha profundizado el conocimiento de los plasmas de TJ-II. También ha acabado de validar el código PRETOR-Stellarator, con lo que se tiene una herramienta útil para la simulación de plasmas de fusión.
In the magnetic confinement cotrolled thermonuclear fusion research it is important to know the energy transport in plasmas, because the transport makes the plasma get cold more or less quickly and so obtain more or less fusion reactions. The energy transport in plasmas is mainly turbulent or anomalous, since now there is not a theory that explains correctly this kind of transport, so in order to make studies and extrapolations it is mandatory to use semiempirical models in validated simulation codes. Among these simulation codes it is PRETOR-Stellarator, used and upgraded during the realization of this thesis.
Another important aspect in the fusion devices are the diagnostics, indispensable tools for understanding the plasma properties of the device. One of the diagnostics installed in the stellarator flexible heliac TJ-II from "Laboratorio Nacional de Fusión" (Madrid) is the charge exchange spectrometer. A deep study and operation of it has been done to analize some of its results during the thesis.
The next generation of fusion devices will improve its features and demonstrate the viability of this technology to produce electricity. To achieve these goals the machines must be bigger than the present-day ones, and therefore more expensive and complex. To avoid these problems some countries have collaborated in the design and, in the future, will collaborate in the construccion of the device. The scientists participating in the construction of the device would acces to the data collected in the machine by remote participation techniques, no matter where their laboratories were. One of the main points of this thesis is the use of remote participation techniques to operate the charge exchange spectrometer, so this can be a good example for the future.
Some electron heat transport studies have been done during this thesis. First of all PRETOR-Stellarator has been validated whit TJ-II shots obtained by remote participation techniques. After, a modification of the code has been done in order to simulate with more precition the central part of the plasma, with these modifications an study of the improved confinement regime of TJ-II has been done.
A series of measurements with the charge exchange spectrometer have been done to comprove the asimetric poloidal ion losses in the plasma. Moreover the influence of an induced current in ion temperature has been investigated.
Finally, with the charge exchange spectrometer data an ion heat transport study has been done. First and study until an effective radius of 0.6 has been done and, after an upgrade of the diagnostic, it has been completed to the last closed flux surface. This last action is a novelty because never has been done in TJ-II. As a main result of these measurements results an ion temperature profile flat along the whole radius, also out of the last closed flux surface.
In this thesis some remote praticipation tools have been tested resulting that they are effective for their use in big scientific instalations. Furthermore the knowledge of TJ-II plasmas has been increased. Also the PRETOR-Stellartor has been validated, resulting an useful tool for the plasma simulations.
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Yokoyama, Masayuki. "Study of Optimized Helical Axis Stellarators." Kyoto University, 1996. http://hdl.handle.net/2433/160805.
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本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものであるKyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第6546号
工博第1556号
新制||工||1045(附属図書館)
UT51-96-T492
京都大学大学院工学研究科原子核工学専攻
(主査)教授 若谷 誠宏, 教授 木村 逸郎, 教授 東 邦夫
学位規則第4条第1項該当
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Landreman, Matthew Joseph. "Electric fields and transport in optimized stellarators." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68874.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 119-124).
Recent stellarator experiments have been designed with one of two types of neoclassical optimization: quasisymmetry or quasi-isodynamism. Both types of stellarator have perfectly confined collisionless particle orbits as well as one additional feature. Quasisymmetric plasmas have minimal flow damping, which may lead to reduced turbulent transport. Quasi-isodynamic plasmas can have vanishing bootstrap current, implying less variation in the magnetic configuration as the pressure changes and also implying greater stability. Analytical expressions for neoclassical transport in a general stellarator are complicated, so it is desirable to find reduced expressions for ideal limiting cases to provide insight. Here, new neoclassical expressions are derived for a quasi-isodynamic plasma. The Pfirsch-Schliiter flow and current can be written concisely as an integral of B. The remaining components of the flow and bootstrap current are identical to those in a quasi-poloidally symmetric device. A compact expression is derived for the radial electric field Er which is largely independent of the details of the magnetic field. Another issue in the neoclassical theory of stellarators which has not been fully resolved is the validity of the so-called monoenergetic approximation, in which ad-hoc changes are made to Er terms in the kinetic equation to expedite numerical computations. Here we show that at least in a quasisymmetric plasma, this approximate treatment of Er leads to a significant and systematic underestimation of the trapped particle fraction. This distortion of the collisionless orbits is independent of any approximations made to the collision operator. For ideal quasisymmetric and quasi-isodynamic plasmas, new neoclassical expressions are derived in which this problematic monoenergetic approximation is avoided. In the quasisymmetric case, results are presented in both the banana regime and plateau regime for the ion flow, ion radial heat flux, and bootstrap current. The bootstrap current is found to be enhanced. For the quasi-isodynamic case, new Er-driven contributions to the distribution function are obtained. The flow and bootstrap current turn out to be modified by the same numerical coefficient as in the quasisymmetric case.
by Matthew Joseph Landreman.
Ph.D.
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Kumar, Santhosh Tekke Athayil. "Experimental studies of magnetic islands, configurations and plasma confinement in the H-1 NF heliac /." View thesis entry in Australian Digital Theses Program, 2007. http://thesis.anu.edu.au/public/adt-ANU20080611.171513/index.html.
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Proll, Josefine Henriette Elise [Verfasser]. "Trapped-particle instabilities in quasi-isodynamic stellarators / Josefine Henriette Elise Proll." Greifswald : Universitätsbibliothek Greifswald, 2014. http://d-nb.info/1047944278/34.
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Vincenzi, Pietro. "Interaction between neutral beam fast particles and plasma in fusion experiments." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424363.
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Neutral beam injection (NBI) is one of the most used and reliable methods to heat plasmas in magnetically confined fusion devices. NBI is used in most of the present experiments, it will be used as dominant auxiliary power system in ITER experiment and studies are ongoing for DEMO reactor preconceptual designs with neutral beam (NB) systems. NBI is an essential actuator for plasma scenarios in terms of heating and driven current. This thesis presents the work performed during the 3 years of my Ph.D.. It focuses on numerical studies of the interaction between energetic particles coming from NBI and magnetically confined hot plasmas. The main aspects discussed in this thesis are the neutral beam ionization, fast ion confinement, fast ion losses, power deposition and driven current. A brief discussion of NBI as fuelling source is also presented. NBI modelling tools have been applied to study different devices with dominant NB power: the largest tokamak in operation (JET), the largest helical device in operation (LHD) and DEMO tokamak reactor concept. Detailed modelling of NBI by means of a Monte Carlo orbit following code has been provided for JET discharge analyses. A predictive simulation aimed at reconstructing the ion temperature profile with strong ion heating from NBI has been performed, resulting in a reliable prediction when the experimental measurement was not available due to a diagnostic fault. JET NBI-plasma interaction has been studied by predictive simulations for H discharges starting from reference D discharges in support of JET isotope studies. The isotopic change and the consequent effect on NBI-plasma interaction has been discussed also for LHD helical device, where studies in preparation of future D experiments (instead of H) are ongoing. NBI is one of the options as additional power system for a demonstrative fusion power plant (DEMO), and a pre-conceptual design of the reactor is ongoing within EUROfusion activities. DEMO scenario simulations have been carried out both for pulsed and steady-state concepts. The role of NBI as dominant heating and current drive system has been investigated by sensitivity studies, comparisons with other heating systems and transport investigations of transient phases (plasma ramp-up and ramp-down).L’iniezione di fasci di particelle neutre (neutral beam injection NBI) é uno dei metodi piú utilizzati e affidabili per scaldare il plasma in esperimenti sulla fusione termonucleare confinata magneticamente. L’NBI é utilizzato nella maggior parte degli attuali esperimenti, verrá applicato come riscaldamento dominante in ITER e studi sono in corso per implementare l’NBI nel progetto europeo del futuro reattore dimostrativo DEMO. L’NBI gioca un ruolo fondamentale per i plasmi fusionistici in termini di riscaldamento e capacitá di indurre corrente nel plasma. Questa tesi presenta il lavoro svolto durante i tre anni del mio dottorato e si focalizza su studi numerici dell’interazione tra particelle energetiche provenienti dall’NBI e plasmi confinati magneticamente. Gli aspetti principali discussi sono la ionizzazione del fascio di neutri nel plasma, il confinamento e le perdite degli ioni veloci, la deposizione di potenza e la corrente di plasma indotta dal fascio. Viene inoltre presentata una breve discussione sull’NBI come sorgente di particelle. Diversi codici numerici sono stati applicati per lo studio di esperimenti caratterizzati da un riscaldamento dominante tramite NBI: sono stati studiati il piú grande tokamak attivo al mondo (JET), il piú grande stellarator attivo al mondo (LHD) e il progetto del reattore dimostrativo europeo DEMO. Accurate simulazioni dell’iniezione del fascio neutro sono state elaborate grazie ad un codice Monte Carlo per l’analisi di esperimenti di JET. Una simulazione predittiva é stata condotta con l’intento di ricostruire il profilo di temperature ionica del plasma nel caso di rilevante riscaldamento ionico da parte dell’NBI. Ció ha prodotto un’attendibile ricostruzione in un caso in cui le misure sperimentali non erano disponibili a causa di un problema con lo strumento di misura. L’interazione tra NBI e plasma al JET é stata studiata tramite simulazioni predittive anche per scariche in idrogeno, partendo da scariche di riferimento in deuterio, con l’obbiettivo di studiare gli effetti che il cambiamento isotopico provoca sul plasma di JET. Studi sugli effetti isotopici sono stati effettuati anche per LHD, esperimento a configurazione elicoidale, dove si stanno preparando i futuri esperimenti in deuterio al posto degli usuali esperimenti in idrogeno. L’iniezione di particelle neutre é una delle opzioni come riscaldamento addizionale del plasma per il futuro reattore dimostrativo DEMO. Attualmente uno studio pre-concettuale di questo reattore é in corso a livello europeo. Simulazioni degli scenari di DEMO sono state effettuate sia per il progetto di un DEMO pulsato, sia per un DEMO a funzionamento stazionario. Il ruolo dell’NBI come riscaldamento principale e sistema per indurre la corrente di plasma é stato investigato tramite studi di sensibilitá, confronti con altri sistemi di riscaldamento e simulazioni delle fasi transitorie del plasma (accensione - ramp-up - e spegnimento - ramp-down - della scarica).
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Cole, Michael David John [Verfasser]. "Global gyrokinetic and fluid hybrid simulations of tokamaks and stellarators / Michael David John Cole." Greifswald : Universitätsbibliothek Greifswald, 2016. http://d-nb.info/1113294698/34.
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Peterson, Joshua T. Knowlton S. F. "Vacuum magnetic flux surface measurements made on the compact toroidal hybrid." Auburn, Ala., 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SUMMER/Physics/Dissertation/Peterson_Joshua_48.pdf.
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Warmer, Felix [Verfasser], Holger [Gutachter] Stark, Dieter [Gutachter] Breitschwerdt, Robert [Gutachter] Wolf, and Hartmut [Gutachter] Zohm. "Integrated concept development of next-step helical-axis advanced stellarators / Felix Warmer ; Gutachter: Holger Stark, Dieter Breitschwerdt, Robert Wolf, Hartmut Zohm." Berlin : Technische Universität Berlin, 2016. http://d-nb.info/1156011965/34.
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Lobsien, Jim-Felix Eduard [Verfasser], Pedersen Thomas [Akademischer Betreuer] Sunn, Pedersen Thomas [Gutachter] Sunn, and David [Gutachter] Bindel. "Tools for designing the next generation of stellarators / Jim-Felix Lobsien ; Gutachter: Thomas Sunn Pedersen, David Bindel ; Betreuer: Thomas Sunn Pedersen." Greifswald : Universität Greifswald, 2020. http://d-nb.info/1217784063/34.
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Lobsien, Jim-Felix [Verfasser], Pedersen Thomas [Akademischer Betreuer] Sunn, Pedersen Thomas [Gutachter] Sunn, and David [Gutachter] Bindel. "Tools for designing the next generation of stellarators / Jim-Felix Lobsien ; Gutachter: Thomas Sunn Pedersen, David Bindel ; Betreuer: Thomas Sunn Pedersen." Greifswald : Universität Greifswald, 2020. http://d-nb.info/1217784063/34.
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Slaby, Christoph [Verfasser], Per [Akademischer Betreuer] Helander, Axel [Akademischer Betreuer] Könies, Ralf [Akademischer Betreuer] Kleiber, Per [Gutachter] Helander, and Laurent [Gutachter] Villard. "Gyro-kinetic simulations of tokamaks and stellarators including collisions / Christoph Slaby ; Gutachter: Per Helander, Laurent Villard ; Per Helander, Axel Könies, Ralf Kleiber." Greifswald : Universität Greifswald, 2019. http://d-nb.info/1185069917/34.
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Slaby, Christoph Verfasser], Per [Akademischer Betreuer] [Helander, Axel Akademischer Betreuer] Könies, Ralf [Akademischer Betreuer] Kleiber, Per [Gutachter] Helander, and Laurent [Gutachter] [Villard. "Gyro-kinetic simulations of tokamaks and stellarators including collisions / Christoph Slaby ; Gutachter: Per Helander, Laurent Villard ; Per Helander, Axel Könies, Ralf Kleiber." Greifswald : Universität Greifswald, 2019. http://d-nb.info/1185069917/34.
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Maurer, Maurice [Verfasser], Frank [Akademischer Betreuer] Jenko, Frank [Gutachter] Jenko, and Eric [Gutachter] Sonnendrücker. "GENE-3D - a global gyrokinetic turbulence code for stellarators and perturbed tokamaks / Maurice Maurer ; Gutachter: Frank Jenko, Eric Sonnendrücker ; Betreuer: Frank Jenko." München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/1215837844/34.
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Abdou, Ali Elsayed Ali Ibrahim. "Superthermal electron dynamics in the HSX stellarator." 2005. http://catalog.hathitrust.org/api/volumes/oclc/76537977.html.
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Dahi, Hossein. "Nonlinear viscosity in the interchangeable module stellarator." 1997. http://catalog.hathitrust.org/api/volumes/oclc/37039060.html.
Full textAbstract:
Thesis (Ph. D.)--University of Wisconsin--Madison, 1997.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 180-183).
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Brenner, Paul. "Confinement of Non-neutral Plasmas in Stellarator Magnetic Surfaces." Thesis, 2011. https://doi.org/10.7916/D8HQ45VQ.
Full textAbstract:
The Columbia Non-neutral Torus (CNT) is the first experiment designed to create and study small Debye length non-neutral plasmas confined by magnetic surfaces. This thesis describes experimental confinement studies of non-neutral plasmas on magnetic surfaces in CNT. Open orbits exist in CNT resulting in electron loss rates that are much faster than initially predicted. For this reason a conforming boundary was designed and installed to address what is believed to be the primary cause of open orbits: the existence of a sizable mismatch between the electrostatic potential surfaces and the magnetic surfaces. After installation a record confinement time of 337 ms was measured, more than an order of magnitude improvement over the previous 20 ms record. This improvement was a combination of the predicted improvement in orbit quality, a reduced Debye length that resulted in decreased transport due to the perturbing insulated rods, and improved operating parameters not indicative of any new physics. The perturbation caused by the insulated rods that hold emitters on axis in CNT is a source of electron transport and would provide a loss mechanism for positrons in future positron-electron plasma experiments. For these reasons an emitter capable of creating plasmas then being removed faster than the confinement time was built and installed. Measurements of plasma decay after emitter retraction indicate that ion accumulation reduces the length of time that plasmas are confined. Plasmas have been measured after retraction with decay times as long as 92 ms after the emitter has left the last closed flux surface. Experimental observations show that obstructing one side of an emitting filament with a nearby insulator substantially improves confinement. As a result, experiments have been performed to determine whether a two stream instability affects confinement in CNT. Results indicate that the improvement is not caused by reducing a two stream instability. Instead, the improvement is a result of altering the sheath of the emitting filament which allows the plasma to reach an equilibrium state with improved confinement. These measurements agree with confinement times for plasmas created by unobstructed emission that are in the same improved confinement state.
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Hammond, Kenneth. "Heating and stability of Columbia Neutral Torus stellarator plasmas." Thesis, 2017. https://doi.org/10.7916/D8833ZKW.
Full textAbstract:
This thesis describes physics research carried out at the Columbia Neutral Torus (CNT) stellarator after its adaptation from a non-neutral plasma experiment to a device relevant to magnetic fusion energy research. Results are presented in the areas of plasma heating and related topics (microwave-assisted plasma start-up, overdense heating, inversion of stellarator images), as well as to stellarator stability and related topics (high β, error fields). This thesis also describes the engineering improvements which enabled the said adaptation of CNT. The first step of that process involved the installation of a low-power, pulsed 2.45 GHz magnetron. In those initial experiments it was found that the simultaneous use of microwave start-up and of an emissive hot cathode resulted in non-linearly increased electron densities, implying a synergy between the two start-up methods. Then, a 10 kW, 2.45 GHz heating system was commissioned including a custom-designed transmission line and launch antenna. Highly overdense plasmas (a factor of 4 above the cutoff density) were obtained with this system, both for O-mode and X-mode polarization. The analysis of Langmuir probe profiles of density and temperature required the accurate mapping of the minor radius in the plasma, which motivated a study of CNT error fields. This resulted in a new numerical method for inferring coil misalignments from flux surface measurements. The improved knowledge of the actual magnetic field geometry of CNT permitted to develop and successfully apply an inversion technique to experimental plasma images. This technique (“onion peeling”) reconstructs radial emissivity profiles, and can be considered a 3D generalization of Abel inversion. Finally, simulations of high-β plasma equilibria in different CNT magnetic configurations indicate that (1) ballooning stability limits should be accessible at volume-averaged β as low as 0.9% and (2) ballooning-stable β values as high as 3.0% should be attainable with heating powers as low as 40-100 kW and 1-3 MW respectively, according to stellarator energy confinement scaling laws.
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Seol, Jaechun. "ECRH and its effects on neoclassical transport in a stellarator." 2007. http://www.library.wisc.edu/databases/connect/dissertations.html.
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Lischtschenko, Oliver [Verfasser]. "Edge biasing in the WEGA stellarator / vorgelegt von Oliver Lischtschenko." 2008. http://d-nb.info/995342598/34.
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Bowden, George. "Damping of Alfvén eigenmodes in complicated tokamak and stellarator geometries." Phd thesis, 2016. http://hdl.handle.net/1885/118247.
Full textAbstract:
A variety of Alfvén wave phenomena are found in toroidal
magnetically confined fusion plasmas. Shear Alfvén eigenmodes
may exist, which can be driven unstable by interaction with
energetic particles. The linear stability of such modes depends
on damping through several mechanisms. Continuum resonances cause
damping of the modes, which occurs even in non-dissipative ideal
magnetohydrodynamic (MHD) theory given appropriate treatment of
resulting poles. Additional damping of the modes occurs due to
conversion to kinetic Alfvén waves and finite parallel electric
fields when kinetic extensions to MHD are considered. In this
thesis, methods for calculating the damping of Alfvén eigenmodes
are developed, with particular focus on the continuum damping
component. Damping of modes in complicated twoand
three-dimensional magnetic geometries characteristic of tokamak
and stellarator plasmas is considered.
In this work, shear Alfvén eigenmodes are analysed based on
reduced MHD models. A background is provided, covering relevant
theoretical aspects of plasma equilibrium, coordinate systems and
linearised MHD waves. A coordinate independent reduced MHD wave
equation is derived for Alfvén eigenmodes in low β tokamaks and
stellarators. Coupled wave equations in terms of Fourier
harmonics of the eigenmode are then derived for large
aspect-ratio plasmas.
Expressions for continuum damping are derived perturbatively from
the coordinate independent and coupled harmonic wave equations.
Application of the expressions using Galerkin and shooting
methods is described. Damping computed in this manner is compared
with values from an accepted method for the benchmark case of a
TAE in a large aspect-ratio circular cross-section tokamak. The
perturbative technique is shown to produce significant errors,
even where continuum damping is small.
A novel singular finite element method is developed to compute
continuum damping. The Galerkin method adopted employs special
basis functions reflecting the asymptotic form of the solution
near continuum resonance poles. For particular eigenmodes, the
unknown complex eigenvalue and pole location are computed
iteratively. The procedure is verified by application to a TAE in
a large aspect-ratio circular cross-section tokamak, where well
converged and accurate complex eigenvalue and mode structure are
obtained.
Continuum damping can be computed numerically by solving the
ideal MHD eigenvalue problem over a complex contour which
circumvents continuum resonance poles according to the causality
condition. This calculation is implemented in the ideal MHD
eigenvalue code CKA, using analytic continuation of equilibrium
quantities. The method is verified through application to a TAE
in a tokamak, where the complex eigenvalue computed agrees
closely with that found using the accepted resistive method, but
converges faster with increasing radial mesh resolution.
Continuum damping of shear Alfvén eigenmodes is computed for
three-dimensional configurations in torsatron, helias and heliac
stellarators.
Extensions to the ideal MHD wave equations allow non-ideal
kinetic effects to be modelled. The damping of a TAE in a tokamak
case through these effects is computed using different models for
magnetic geometry and kinetic effects. Choice of the former
strongly influences results, while choice of the latter does not.
Damping from kinetic effects is also computed for an NGAE in a
heliac.
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Matthews, Peter Gerhard. "Fluctuation-induced transport and poloidal rotation in the interchangeable module stellarator." 1993. http://catalog.hathitrust.org/api/volumes/oclc/30843386.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1993.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 200-203).
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Doerner, Russell P. "The divertor structure and particle control in the interchangeable module stellarator." 1988. http://catalog.hathitrust.org/api/volumes/oclc/19966687.html.
Full textAbstract:
Thesis (Ph. D.)--University of Wisconsin--Madison, 1988.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 150-154).
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Anuj, Chaudhri. "Thermal modeling and verification of a quasi-poloidal stellarator modular coil." 2004. http://etd.utk.edu/2004/ChaudhriAnuj.pdf.
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Thesis (M.S.)--University of Tennessee, Knoxville, 2004.Title from title page screen (viewed Sept. 23, 2004). Thesis advisor: Masood Parang. Document formatted into pages (xxii, 162 p. : ill. (some color)). Vita. Includes bibliographical references (p. 147-150).
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Trost, Peter Karl. "Electron behavior during electron cyclotron resonance heating in the Interchangeable Module Stellarator." 1988. http://catalog.hathitrust.org/api/volumes/oclc/18945501.html.
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Marsen, Stefan [Verfasser]. "The spatio-temporal structure of electrostatic turbulence in the WEGA stellarator / vorgelegt von Stefan Marsen." 2008. http://d-nb.info/98959436X/34.
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Peterson, Byron Jay. "The measurement of parallel electron currents and induced ion flows in the interchangeable module stellarator." 1994. http://catalog.hathitrust.org/api/volumes/oclc/31514126.html.
Full textAbstract:
Thesis (Ph. D.)--University of Wisconsin--Madison, 1994.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 170-175).
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Hussein, Makarem Ali Ibrahim. "Plasma flow in a divergent magnetic field with applications to stellarator edge and electron clyclotron resonance etching plasmas." 1990. http://catalog.hathitrust.org/api/volumes/oclc/22948121.html.
Full textAbstract:
Thesis (Ph. D.)--University of Wisconsin--Madison, 1990.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.
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Glass, Fenton John. "Tomographic Visible Spectroscopy of Plasma Emissivity and Ion Temperatures." Phd thesis, 2004. http://hdl.handle.net/1885/47104.
Full textAbstract:
Extending the use of Doppler spectroscopy as an important plasma diagnostic -- by developing a multi-channel system capable of tomography -- is the foundation of this thesis. A system which can simultaneously measure the emissivity, temperature and flow velocity of plasma ions has been installed, calibrated and operated on the H-1NF heliac, yielding comprehensive and interesting results. The measurements are time-resolved, made from a large range of viewing positions and, using scalar tomographic inversion methods, can be unfolded to give two-dimensional images of ion emissivity and temperature. The flow velocity profiles, while not inverted, nevertheless lead to a greater understanding of the plasma behaviour.¶ ...