Dissertations / Theses on the topic 'Ion cyclotron waves'
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Teodorescu, Catalin. "Laboratory investigation of electrostatic ion waves modified by parallel-ion-velocity shear." Morgantown, W. Va. : [West Virginia University Libraries], 2003. http://etd.wvu.edu/templates/showETD.cfm?recnum=2901.
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Thesis (Ph. D.)--West Virginia University, 2003.Title from document title page. Document formatted into pages; contains xiv, 215 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 107-113).
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Nguyen, Son Thanh Perez Joseph D. "Interactions between electromagnetic ion cyclotron waves and protons in the magnetosphere SCATHA Results /." Auburn, Ala., 2007. http://hdl.handle.net/10415/1380.
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Hannan, Abdul. "Modelling Ion Cyclotron Resonance Heating and Fast Wave Current Drive in Tokamaks." Doctoral thesis, KTH, Fusionsplasmafysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-119930.
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Fast magnetosonic waves in the ion cyclotron range of frequencies have the potential to heat plasma and drive current in a thermonuclear fusion reactor. A code, SELFO-light, has been developed to study the physics of ion cyclotron resonantheating and current drive in thermonuclear fusion reactors. It uses a global full wave solver LION and a new 1D Fokker-Planck solver for the self-consistent calculations of the wave field and the distribution function of ions.In present day tokamak experiments like DIII-D and JET, fast wave damping by ions at higher harmonic cyclotron frequencies is weak compared to future thermonuclear tokamak reactors like DEMO. The strong damping by deuterium, tritium and thermonuclear alpha-particles and the large Doppler width of fast alpha-particles in DEMO makes it difficult to drive the current when harmonic resonance layers of these ionspecies are located at low field side of the magnetic axis. At higher harmonic frequencies the possibility of fast wave current drive diminishes due to the overlapping of alpha-particle harmonic resonance layers. Narrow frequency bands suitable for the fast wave current drive in DEMO have been identified at lower harmonics of the alpha-particles. For these frequencies the effect of formation of high-energy tails in the distribution function of majority and minority ion species on the current drive have been studied. Some of these frequencies are found to provide efficient ion heating in the start up phase of DEMO. The spectrum where efficient current drive can be obtained is restricted due to weak electron damping at lower toroidal mode numbers and strong trapped electron damping at higher toroidal mode numbers. The width of toroidal mode spectra for which efficient current drive can be obtained have been identified, which has important implications for the antenna design.QC 20130327
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De, Soria-Santacruz Pich Maria. "Controlled precipitation of energetic Van Allen belt protons by electromagnetic ion cyclotron (EMIC) waves : scientific and engineering implications." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87127.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 235-247).
The inner Van Allen radiation belt traps highly energetic protons sourced from solar storms, cosmic rays and other processes. These particles can rapidly damage the space systems orbiting the inner region, limiting access to Low Earth Orbit (LEO). Decades of modeling and observations, however, show that naturally generated ULF/VLF waves have the capability of precipitating energetic trapped electrons and protons. This fact suggests that there could be human control over the stable inner belt proton population by artificially transmitting Electromagnetic Ion Cyclotron (EMIC) waves from space-based antennas (named remediation). These waves are naturally generated by equatorial ring current ions in the outer belt region, which explains the absence of EMIC waves at lower altitudes. Consequently, the precipitation of high-energy protons requires artificial generation of EMIC waves into the inner zone. The controlled removal of energetic outer belt electrons by man-made whistler waves has been widely studied, and a space test of a linear antenna for this purpose is in preparation. Contrarily, the interaction between inner belt protons and EMIC waves from in-situ transmitters is an unexplored solution to the radiation environment that should be addressed given its relevance to the scientific and engineering communities. This dissertation focuses on four interconnected research efforts in this direction, which are (1) the radiation of EMIC waves from a space-based antenna, (2) the propagation of these waves in the inner radiation belt, (3) the wave-particle interactions with energetic trapped protons and (4) the feasibility of a mission capable of significantly reducing this hazardous radiation. Our analyses show that a DC rotating coil antenna would be capable of radiating EMIC waves into space. Magnetic dipoles, however, have a very small radiation resistance. Additionally, the interaction between these waves and energetic protons is very inefficient. Our simulations show that, with the current technology, it is not engineeringly feasible to clean up the proton belt using space-based transmitters. A mission scaled down to detectability of the precipitating protons, however, could be launched easily and would allow us to better understand the science and test the technology involved in the concept of remediation.
by Maria de Soria-Santacruz Pich.
Ph. D.
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Urbanczyk, Guillaume. "Interaction of High-Power waves with the plasma periphery of WEST & EAST tokamaks." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0181.
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Cette thèse vise à étudier les interactions entre le plasma et les parois de tokamaks liées aux ondes à la fréquence cyclotronique ionique (FCI), les interactions plasma-métaux étant à éviter absolument car elles sont synonymes de dégradations matérielles de l’enceinte et la libération d’impuretés métalliques dans le plasma dont les performances s’en trouvent grandement réduites. Cette problématique affecte concrètement toute machine visant à chauffer les ions via des ondes à la fréquence FCI, ce qui sera notamment le cas d’ITER. Cette thèse s'inscrit dans une collaboration entre le CEA Cadarache (France) et l’Institut de Physique des Plasmas à Hefei (Chine). Divers travaux expérimentaux ont été effectués sur les tokamaks EAST (Chine) et WEST (France) afin d'identifier les paramètres pertinents pour d'une part optimiser l'efficacité par laquelle les ondes FCI utilisées pour chauffer le plasma doivent être excitées afin de maximiser la quantité de puissance couplée au plasma tout en minimisant les interactions du plasma avec les parois dues à ce type d'ondes et souvent attribuées au concept de gaine radiofréquence au cœur de cette thèseThis thesis aims at studying phenomena by which Ion Cyclotron Resonance Heating (ICRH) induces interactions between the plasma and the walls of tokamaks, the plasma-metal interactions being deleterious not only to prevent vessel materials degradation but also not to affect plasma performance due to the presence of heavy metallic impurity compared to foreseen fuel (namely deuterium and tritium). This problematic basically affects any machine aiming at heating the ions with waves at the ion cyclotron frequency, which in particular will be the case of ITER. This thesis is the result of a collaboration between CEA Cadarache (France) and the Institute of Plasma Physics in Hefei (China). Various experimental work have been carried out on the EAST (China) and WEST (France) tokamaks in order to identify the relevant parameters allowing to optimize the efficiency by which the ICRF waves – used to heat the plasma – must be excited in order to maximize the amount of power coupled, while simultaneously minimizing the plasma interactions with the walls due to this type of waves and the so called radiofrequency sheath excitation
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Kwon, Myeun. "Fast wave ion cyclotron resonance heating experiments on the advanced toroidal facility." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/13015.
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Hedin, Johan. "Ion cyclotron resonance heating in toroidal plasmas." Doctoral thesis, KTH, Alfvén Laboratory, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3073.
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Shepard, Thomas Donavon. "Fast wave ion cyclotron resonance heating experiments on the Alcator C tokamak." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14402.
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Johnson, Thomas. "Fast wave heating of cyclotron resonant ions in tokamaks." Doctoral thesis, KTH, Alfvénlaboratoriet, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3771.
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Chang, Ouliang. "Numerical Simulation of Ion-Cyclotron Turbulence Generated by Artificial Plasma Cloud Release." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/34018.
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Possibilities of generating plasma turbulence to provide control of space weather processes have been of particular interest in recent years. Such turbulence can be created by chemical released into a magnetized background plasma. The released plasma clouds are heavy ions which have ring velocity distribution and large free energy to drive the turbulence. An electromagnetic hybrid (fluid electrons and particle ions) model incorporating electron inertia is developed to study the generation and nonlinear evolution of this turbulence. Fourier pseudo-spectral methods are combined with finite difference methods to solve the electron momentum equations. Time integration is accomplished by a 4th-order Runge-Kutta scheme or predicator-corrector method. The numerical results show good agreement with theoretical prediction as well as provide further insights on the nonlinear turbulence evolution. Initially the turbulence lies near harmonics of the ring plasma ion cyclotron frequency and propagates nearly perpendicular to the background magnetic field as predicted by the linear theory. If the amplitude of the turbulence is sufficiently large, the quasi-electrostatic short wavelength ion cyclotron waves evolve nonlinearly into electromagnetic obliquely propagating shear Alfven waves with much longer wavelength. The results indicate that ring densities above a few percent of the background plasma density may produce wave amplitudes large enough for such an evolution to occur. The extraction of energy from the ring plasma may be in the range of 10-15% with a generally slight decrease in the magnitude as the ring density is increased from a few percent to several 10's of percent of the background plasma density. Possibilities to model the effects of nonlinear processes on energy extraction by introducing electron anomalous resistivity are also addressed. Suitability of the nonlinearly generated shear Alfven waves for applications to scattering radiation belt particles is discussed.Master of Science
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Kubota, Yuko. "Study on Variation of Radiation Belt Electron Fluxes Through Nonlinear Wave-Particle Interactions." Kyoto University, 2018. http://hdl.handle.net/2433/232003.
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Lu, LingFeng. "Modelling of plasma-antenna coupling and non-linear radio frequency wave-plasma-wall interactions in the magnetized plasma device under ion cyclotron range of frequencies." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0173/document.
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Le Chauffage Cyclotron Ionique (ICRH) par des ondes dans la gamme 30-80MHz est couramment utilisé dans les plasmas de fusion magnétique. Excitées par par des réseaux phasés de rubans de courant à la périphérie du plasma, ces ondes existent sous deux polarisations. L’onde rapide traverse le bord ténu du plasma par effet tunnel puis se propage à son centre où elle est absorbée. L’onde lente, émise de façon parasite, existe seulement à proximité des antennes. Quelle puissance peut être couplée au centre avec 1A de courant sur les rubans? Comment les champs radiofréquence (RF) proches et lointains émis interagissent-ils avec le plasma de bord par rectification de gaine RF à l’interface plasma-paroi? Pour répondre simultanément à ces deux questions, en géométrie réaliste sur l’échelle spatiale des antennes ICRH, cette thèse a amélioré et testé le code numérique SSWICH (Self-consitent Sheaths and Waves for ICH). SSWICH couple de manière auto-cohérente la propagation des ondes RF et la polarisation continue (DC) du plasma via des conditions aux limites non-linéaires de type gaine (SBC) appliquées à l’interface plasma / paroi. La nouvelle version SSWICH-FW est pleine onde et a été développée en deux dimensions (toroïdale/radiale). De nouvelles SBCs couplant les deux polarisations d’ondes ont été obtenues et mises en œuvre le long de parois courbes inclinées par rapport au champ magnétique de confinement. Avec ce nouvel outil en l'absence de SBCs, nous avons étudié l'impact d'une densité décroissant continûment à l'intérieur de la boîte d'antenne en traversant la résonance hybride basse (LH). Dans les limites mémoire de notre poste de travail, les champs RF au-dessous de la résonance LH ont changé avec la taille de maille. Par contre spectre de puissance couplée n’a que très peu évolué, et n’était que faiblement influencé par la densité à l'intérieur de l'antenne. En présence de SBCs, les simulations SSWICH-FW ont identifié le rôle de l'onde rapide sur l’excitation de gaines RF et reproduit certaines observations expérimentales clés. SSWICH-FW a finalement été adapté pour réaliser les premières simulations 2D électromagnétiques et de gaine-RF de la machine plasma cylindrique magnétisée ALINEIon Cyclotron Resonant Heating (ICRH) by waves in 30-80MHz range is currently used in magnetic fusion plasmas. Excited by phased arrays of current straps at the plasma periphery, these waves exist under two polarizations. The Fast Wave tunnels through the tenuous plasma edge and propagates to its center where it is absorbed. The parasitically emitted Slow Wave only exists close to the launchers. How much power can be coupled to the center with 1A current on the straps? How do the emitted radiofrequency (RF) near and far fields interact parasitically with the edge plasma via RF sheath rectification at plasma-wall interfaces? To address these two issues simultaneously, in realistic geometry over the size of ICRH antennas, this thesis upgraded and tested the Self-consistent Sheaths and Waves for ICH (SSWICH) code. SSWICH couples self-consistently RF wave propagation and Direct Current (DC) plasma biasing via non-linear RF and DC sheath boundary conditions (SBCs) at plasma/wall interfaces. Its upgrade is full wave and was implemented in two dimensions (toroidal/radial). New SBCs coupling the two polarizations were derived and implemented along shaped walls tilted with respect to the confinement magnetic field. Using this new tool in the absence of SBCs, we studied the impact of a density decaying continuously inside the antenna box and across the Lower Hybrid (LH) resonance. Up to the memory limits of our workstation, the RF fields below the LH resonance changed with the grid size. However the coupled power spectrum hardly evolved and was only weakly affected by the density inside the box. In presence of SBCs, SSWICH-FW simulations have identified the role of the fast wave on RF sheath excitation and reproduced some key experimental observations. SSWICH-FW was finally adapted to conduct the first electromagnetic and RF-sheath 2D simulations of the cylindrical magnetized plasma device ALINE
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Suárez, López Guillermo [Verfasser], and Hartmut [Akademischer Betreuer] Zohm. "Effect of non-axisymmetric tokamak plasmas on the coupling performance of ion cyclotron wave antennas / Guillermo Suárez López ; Betreuer: Hartmut Zohm." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2020. http://d-nb.info/1227840101/34.
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Laxåback, Martin. "Fast wave heating and current drive in tokamaks." Doctoral thesis, KTH, Alfvénlaboratoriet, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118.
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This thesis concerns heating and current drive in tokamak plasmas using the fast magnetosonic wave in the ion cyclotron range of frequencies. Fast wave heating is a versatile heating method for thermonuclear fusion plasmas and can provide both ion and electron heating and non-inductive current drive. Predicting and interpreting realistic heating scenarios is however difficult due to the coupled evolution of the cyclotron resonant ion velocity distributions and the wave field. The SELFO code, which solves the coupled wave equation and Fokker-Planck equation for cyclotron resonant ion species in a self-consistent manner, has been upgraded to allow the study of more advanced fast wave heating and current drive scenarios in present day experiments and in preparation for the ITER tokamak. Theoretical and experimental studies related to fast wave heating and current drive with emphasis on fast ion effects are presented. Analysis of minority ion cyclotron current drive in ITER indicates that the use of a hydrogen minority rather than the proposed helium-3 minority results in substantially more efficient current drive. The parasitic losses of power to fusion born alpha particles and beam injected ions are concluded to be acceptably low. Experiments performed at the JET tokamak on polychromatic ion cyclotron resonance heating and on fast wave electron current drive are presented and analysed. Polychromatic heating is demonstrated to increase the bulk plasma ion to electron heating ratio, in line with theoretical expectations, but the fast wave electron current drive is found to be severely degraded by parasitic power losses outside of the plasma. A theoretical analysis of parasitic power losses at radio frequency antennas indicates that the losses can be significantly increased in scenarios with low wave damping and with narrow antenna spectra, such as in electron current drive scenarios.QC 20100506
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Yeh-WeiYang and 楊業葳. "Crossover Frequencies of Ion-Cyclotron Waves in Three-Ion Plasmas." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/89097522212204791578.
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碩士國立成功大學
太空與電漿科學研究所
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The crossover frequency in plasma is a frequency at which the wave can change polarization and convert to another mode such as from right-hand whistler-mode to left-hand ion-cyclotron waves when the wave vector is parallel to the field lines. This frequency occurs in multi-ion plasma and their values would vary as the compositions/percentages of background ion species vary. In the thesis, we not only derive the 2-ion and 3-ion plasma’s formula of the crossover frequency but also use the crossover frequencies of ion whistlers observed by DEMETER satellite to calculate the percentages of each ion species at the observational site. Finally, for further application to analyze data from satellite missions, the crossover frequencies over different percentages for each ion species are normalize to proton gyrofrequency.
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Yi-LingLin and 林怡伶. "Distribution of Water Group Ion Cyclotron Waves in Saturn’s Magnetosphere." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/18256004348265729748.
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Usanova, Maria. "Generation of Electromagnetic Ion Cyclotron (EMIC)Waves in a Compressed Dayside Magnetosphere." Phd thesis, 2010. http://hdl.handle.net/10048/1525.
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Electromagnetic Ion Cyclotron (EMIC) waves are believed to play an important
role in the dynamics of energetic particles (both electrons and ions) trapped
by the Earths magnetic field causing them to precipitate into the ionosphere via resonant interaction. In order to incorporate the EMIC-related loss processes into global magnetospheric models one needs to know solar wind and magnetospheric conditions favourable for EMIC wave excitation as well as the localization of the waves in the magnetosphere. EMIC waves are generated by anisotropic (Tperp/Tpara > 1) ion distributions. Generally, any process that leads to the formation of such distributions may be responsible for EMIC wave initiation. This thesis discusses magnetospheric compression as a new principal source of EMIC wave generation in the inner dayside magnetosphere.
First, using ground-based and satellite instrumentation, it is shown that EMIC
waves are often generated in the inner dayside magnetosphere during periods
of enhanced solar wind dynamic pressure and associated dayside magnetospheric compression. The compression-related EMIC wave activity usually lasts for several hours while the magnetosphere remains compressed. Also, it is demonstrated that EMIC waves are generated in radially narrow (1 Re wide) region of high plasma density, just inside the plasmapause.
Test particle simulations of energetic ion dynamics performed for this study
confirmed that anisotropic ion distributions are generated in the compressed
dayside magnetosphere, the temperature anisotropy being dependant on the
strength of magnetospheric compression. It is found that in the inner magnetosphere these anisotropic particle distributions are formed due to particle drift shell-splitting in an asymmetric magnetic field.
Finally, the generation of EMIC waves was studied self-consistently using a
hybrid particle-in-cell code in order to determine whether the degree of anisotropy estimated from the test particle simulations is sufficient to produce EMIC waves like those detected and to explain some of the observed wave properties.
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Capannolo, Luisa. "Energetic electron precipitation into the Earth's upper atmosphere driven by electromagnetic ion cyclotron waves." Thesis, 2020. https://hdl.handle.net/2144/40353.
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Energetic electrons undergo significant flux variations in the Earth’s outer radiation belt, where magnetospheric waves play an important role in changing the energetic electron dynamics. In particular, electromagnetic ion cyclotron (EMIC) waves are suggested to drive efficient pitch angle scattering of relativistic electrons, which results in relativistic electron precipitation into the upper atmosphere. Such precipitation provides an important source of energy input into the upper atmosphere, where precipitating electrons can affect atmospheric chemistry and ionization. However, the quantitative role of EMIC waves in energetic electron precipitation in various regions of the magnetosphere is not fully understood. This dissertation aims to answer outstanding open questions on the characteristics and quantification of EMIC-driven precipitation, such as the spatial extent and the energy range of electron precipitation. The relationship between EMIC waves and electron precipitation is evaluated by analyzing magnetic conjunction events when EMIC waves are detected in the magnetosphere by near-equatorial satellites (Van Allen Probes, GOES) and precipitating electrons are measured by Low-Earth-Orbiting satellites (POES, FIREBIRD). Quasi-linear theory is used to quantify the role of various observed magnetospheric waves (e.g., EMIC waves, plasmaspheric hiss, magnetosonic waves) in the electron precipitation. Several in-depth case analyses show that EMIC waves are the main driver of the observed relativistic electron precipitation, while other waves play a minor role. The precipitation events were clearly identified within L shell of ~7.5, favorably near the dusk and night sectors. The analysis shows that each precipitation event was localized on average spatial scales of ~0.3 L, suggesting that the resonance conditions are satisfied in a very localized region of the magnetosphere. The electron precipitation was observed at the expected relativistic (> ~MeV) energies; however, the minimum energy of efficient electron precipitation was newly found to extend down to at least ~200–300 keV. The quantitative analysis using multi-point measurements combined with theoretical calculations in this dissertation provides a more comprehensive understanding of EMIC-driven precipitation, which is a critical electron loss process in the magnetosphere. Moreover, the results are helpful to improve currently existing models of radiation belt, ring current and atmosphere dynamics, as well as theories of wave-particle interactions.
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Browning, Jim. "Interchange stabilization of a mirror plasma using radio-frequency waves below the ion cyclotron frequency." 1988. http://catalog.hathitrust.org/api/volumes/oclc/19491617.html.
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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 108-114).
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Sund, Richard Stewart. "Power conservation for linear waves in the ion-cyclotron range of frequencies in nonuniform hot plasmas." 1986. http://catalog.hathitrust.org/api/volumes/oclc/15598410.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1986.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 63-64).
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Halford, Alexa J. "EMIC wave association with gepmagnetic storms, the plasmasphere, and the radiation belts." Thesis, 2012. http://hdl.handle.net/1959.13/933260.
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Research Doctorate - Doctor of Philosophy (PhD)Electromagnetic Ion Cyclotron (EMIC) waves have recently been considered an important process in the magnetosphere and in particular contribute to electron loss in the radiation belts. Here we describe the characteristics of EMIC waves under different magnetospheric conditions, their relationship to the plasmasphere and plasmaspheric plumes, and start examining the ability of EMIC waves to resonate with radiation belt electrons using data from the Combined Release and Radiation Effect Satellite (CRRES). The CRRES mission was operational from 25 July, 1990 until 21 October, 1991. It had an orbital period of 9 hrs and 52 minutes and was able to observe the magnetospheric region of 3 < L < 8, magnetic local times (MLT) between 14:00 - 08:00 hr, and magnetic latitudes (Mlat) between ±30. CRRES observed 913 EMIC waves and 124 geomagnetic storms. Due to the lack of coverage around noon, the majority of EMIC waves were found to occur in the dusk sector at MLT = 15 hr and at L = 6. The highest occurrence rates for EMIC waves occurred during the main phase of geomagnetic storms, when it is expected that there may be overlap between the cold plasmaspheric plasma and the hot ring current plasma. The role of the cold plasmaspheric plasma has been examined. It was found that EMIC waves were observed in regions with enhanced cold plasma densities under all magneto- spheric conditions except for the pre-onset phase of a geomagnetic storm, which may be due to the small number of events. As CRRES was not always able to observe the bound- aries of either the plasmasphere or a plasmaspheric plume during each orbit, a superposed epoch was created of the observed densities at L-values between 3 and 8 for the region between 14 hr< MLT <18 hr, the region where plasmaspheric plumes are expected to be observed, for each phase of the 124 geomagnetic storms observed by CRRES. Dur- ing the main phase of the geomagnetic storms, an increase in the plasmaspheric number density was observed between 5 < L < 7. This is consistent with the idea of plasmas- pheric plumes forming during this phase. However, the mean location of the EMIC wave events during the main phase of a geomagnetic storm falls in the middle of the plume, not on the boundary as suggested by some theories. It has been predicted that EMIC waves need negative density gradients in order to grow to observable levels and to propagate effectively through the magnetosphere. No significant correlation between local density gradients and the occurrence of EMIC waves was found. EMIC waves have been suggested as a mechanism for electron particle loss in the radiation belts. It was found that for electrons with energies of 1.25 - 10 MeV, there were EMIC wave events where the pitch angle diffusion extended into the loss cone. It is expected that after bounce averaging the diffusion coefficients will exceed the strong diffusion regime under most magnetospheric conditions for electron energies between 1.25 and 2 MeV. On average the highest diffusion coefficients were observed during the main phase of geomagnetic storms. CRRES has greatly increased the communities understanding of EMIC waves and their role within the Earth-Space environment. It has been shown where and when to expect to see these waves, how plumes, but more importantly enhanced cold plasma den- sities, play a large role in EMIC wave occurrence, and how EMIC waves are able to resonate with radiation belt electrons contributing to the main phase loss in the radiation belts. This thesis concludes with a look towards continuations of this work and future research projects which will help address some of the raised and unanswered questions throughout the thesis.
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Lee, Jar-Lon. "Wave coupling and matching of waveguide couplers in the ion cyclotron range of frequencies." 1988. http://catalog.hathitrust.org/api/volumes/oclc/19403076.html.
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Lafleur, Trevor. "Helicon Wave Propagation in Low Diverging Magnetic Fields." Phd thesis, 2011. http://hdl.handle.net/1885/8676.
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This thesis details an experimental, theoretical, and numerical investigation into helicon wave propagation in the presence of low diverging magnetic fields (< 5 m T). Experiments are performed in the Piglet helicon reactor, which consists of a Pyrex source tube connected to a larger aluminium diffusion chamber. A double-saddle field antenna (operated at 13.56 MHz), is used to create both the plasma and launch helicon waves, while the diverging magnetic field is produced by a number of solenoids that surround both the antenna and source tube. Experiments are conducted with argon gas in the pressure range 0.04-0.4 Pa, and for rf input powers below 400 W.
As the magnetic field is increased (using single solenoid), the plasma density is observed to increase rapidly over a narrow range of magnetic values (between about 1 mT < Bo < 5 mT), where a distinct density peak is formed. The density at the maximum of the peak (>1017 m-3 ) is more than an order of magnitude larger than that before or after, and is associated with a corresponding peak in the measured antenna resistance; showing that a larger percentage of the input power is deposited within the plasma.
In the presence of the diverging magnetic field an ion beam is observed to form simultaneously with the low –field helicon mode. The ion beam, which is present for argon gas pressures below around 0.3 Pa, is produced by upstream ions accelerated by a decreasing plasma potential set up by the spatially decaying plasma density profile. An analytical model, based on simple flux conservation, is developed to describe the general features and behaviour of the observed ion energy distribution functions (IEDFs), which are found to be strong functions of the plasma potential profile and neutral gas pressure.
During the low-field mode, m = 1 helicon waves was observed with B-dot probes in the source region of Piglet. With just a single solenoid producing the magnetic field, waves are prevented reaching the downstream region (that is, the waves appear “trapped”), but slight modifications to the magnetic field geometry allows the axial distance over which waves can propagate to be controlled. Critical to the modification of the wave propagation behaviour is the magnetic field strength ( and geometry) near the exit of the plasma source region, which gives electron cyclotron frequencies close to the wave frequency of 13.56MHz.
By solving the wave equation using cold plasma approximation, and separately by making use of a 1D electromagnetic particle-in-cell (PIC) simulation, wave propagation and absorption are investigated in the presence of a low diverging magnetic field. The numerical results from both studies are in good qualitative agreement with the experimental measurements, and provide strong evidence to suggest that the observed wave “trapping” is due to electron cyclotron damping of helicon waves in the spatially decaying magnetic field; an electron heating process not usually dominant in conventional helicon discharges, thus opening up additional possibilities for the use and optimization of helicon systems in processing and propulsion applications.