Letteratura scientifica selezionata sul tema "Electrons découplés companion plasma"
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Articoli di riviste sul tema "Electrons découplés companion plasma":
1
Istomin, Ya N. "On the Nature of Radio Eclipsing". International Astronomical Union Colloquium 177 (2000): 533–34. http://dx.doi.org/10.1017/s025292110006053x.
Abstract (sommario):
AbstractIt is shown that the phenomena of radio eclipsing can be explained by the linear mechanism of transformation of the transverse electromagnetic wave, propagating in the pulsar wind, into the plasma waves in the region of interaction of wind with a companion star atmosphere. The coefficient of the passingηdepends on the wave frequencyωby the exponential mannerη= exp{–const ·ω−1}. The estimated scale for the pulsar wind and star’s atmosphere density gradients are of the order of 100 meters. Such gradient can be obtained in the bow shock forming when the pulsar wind enters into the companion star atmosphere. Annihilation of the part of the wind’s positrons with the star’s electrons produces the electric current. This current generates the magnetic field from which the pulsar wind’s particles are reflected. The magnitude of the magnetic field in this shock of about several Gauss.
2
Papavasileiou, Theodora, Odysseas Kosmas e Ioannis Sinatkas. "Studying the Spectral Energy Distributions Emanating from Regular Galactic XRBs". Universe 9, n. 7 (28 giugno 2023): 312. http://dx.doi.org/10.3390/universe9070312.
Abstract (sommario):
X-ray binary systems (XRBs) exhibit similar dynamics and multimessenger emission mechanisms to active galactic nuclei (AGNs) with the benefit of shorter time scaling. Those systems produce rich spectral energy distributions (SEDs) ranging from the radio band to the very high energy gamma rays. The emission origin varies between the system’s accretion disk (X-rays) to the corona and, most notably, to the two twin plasma ejections (jets) that often meet the interstellar medium forming highly observable radio lobes. Modeling of the jets offers an excellent opportunity to understand the intrinsic mechanisms and the jet particles, such as electrons, positrons, and protons. In this work, we employ a lepto-hadronic jet model that assumes particle acceleration through shock waves over separate zonal regions of the jet. The hadronic models consider proton–proton collisions that end up in gamma-ray photons through neutral pion decays. The main leptonic mechanisms involve synchrotron radiation (from both electrons and protons) and inverse Compton scattering of ambient photons (coming from the disk, the corona, and the companion star) on jet electrons. The emissions from the disk, the corona, and the donor star are also included in the SED calculations, along with the photon absorption effects due to their interaction with higher-energy jet photons. We apply the model on a 10M⊙ black hole accreting at the Eddington rate out of a 20M⊙ companion star. One of our goals is to investigate and determine an optimal frame concerning the values for the free parameters that enter our calculations to produce higher integral fluxes.
3
Reux, C., C. Paz-Soldan, N. Eidietis, M. Lehnen, P. Aleynikov, S. Silburn, V. Bandaru et al. "Physics of runaway electrons with shattered pellet injection at JET". Plasma Physics and Controlled Fusion 64, n. 3 (2 febbraio 2022): 034002. http://dx.doi.org/10.1088/1361-6587/ac48bc.
Abstract (sommario):
Abstract Runaway electrons (REs) created during tokamak disruptions pose a threat to the reliable operation of future larger machines. Experiments using shattered pellet injection (SPI) have been carried out at the JET tokamak to investigate ways to prevent their generation or suppress them if avoidance is not sufficient. Avoidance is possible if the SPI contains a sufficiently low fraction of high-Z material, or if it is fired early in advance of a disruption prone to runaway generation. These results are consistent with previous similar findings obtained with Massive Gas Injection. Suppression of an already accelerated beam is not efficient using High-Z material, but deuterium leads to harmless terminations without heat loads. This effect is due to the combination of a large magnetohydrodynamic instability scattering REs on a large area and the absence of runaway regeneration during the subsequent current collapse thanks to the flushing of high-Z impurities from the runaway companion plasma. This effect also works in situations where the runaway beam moves upwards and undergoes scraping-off on the wall.
4
Ma, Q., B. Ni, X. Tao e R. M. Thorne. "Evolution of the plasma sheet electron pitch angle distribution by whistler-mode chorus waves in non-dipole magnetic fields". Annales Geophysicae 30, n. 4 (27 aprile 2012): 751–60. http://dx.doi.org/10.5194/angeo-30-751-2012.
Abstract (sommario):
Abstract. We present a detailed numerical study on the effects of a non-dipole magnetic field on the Earth's plasma sheet electron distribution and its implication for diffuse auroral precipitation. Use of the modified bounce-averaged Fokker-Planck equation developed in the companion paper by Ni et al. (2012) for 2-D non-dipole magnetic fields suggests that we can adopt a numerical scheme similar to that used for a dipole field, but should evaluate bounce-averaged diffusion coefficients and bounce period related terms in non-dipole magnetic fields. Focusing on nightside whistler-mode chorus waves at L = 6, and using various Dungey magnetic models, we calculate and compare of the bounce-averaged diffusion coefficients in each case. Using the Alternative Direction Implicit (ADI) scheme to numerically solve the 2-D Fokker-Planck diffusion equation, we demonstrate that chorus driven resonant scattering causes plasma sheet electrons to be scattered much faster into loss cone in a non-dipole field than a dipole. The electrons subject to such scattering extends to lower energies and higher equatorial pitch angles when the southward interplanetary magnetic field (IMF) increases in the Dungey magnetic model. Furthermore, we find that changes in the diffusion coefficients are the dominant factor responsible for variations in the modeled temporal evolution of plasma sheet electron distribution. Our study demonstrates that the effects of realistic ambient magnetic fields need to be incorporated into both the evaluation of resonant diffusion coefficients and the calculation of Fokker-Planck diffusion equation to understand quantitatively the evolution of plasma sheet electron distribution and the occurrence of diffuse aurora, in particular at L > 5 during geomagnetically disturbed periods when the ambient magnetic field considerably deviates from a magnetic dipole.
5
Bouhram, M., N. Dubouloz, M. Hamelin, S. A. Grigoriev, M. Malingre, K. Torkar, M. V. Veselov et al. "Electrostatic interaction between Interball-2 and the ambient plasma. 1. Determination of the spacecraft potential from current calculations". Annales Geophysicae 20, n. 3 (31 marzo 2002): 365–76. http://dx.doi.org/10.5194/angeo-20-365-2002.
Abstract (sommario):
Abstract. The Interball-2 spacecraft travels at altitudes extending up to 20 000 km, and becomes positively charged due to the low-plasma densities encountered and the photoemission on its sunlit surface. Therefore, a knowledge of the spacecraft potential Fs is required for correcting accurately thermal ion measurements on Interball-2. The determination of Fs is based on the balance of currents between escaping photoelectrons and incoming plasma electrons. A three-dimensional model of the potential structure surrounding Interball-2, including a realistic geometry and neglecting the space-charge densities, is used to find, through particle simulations, current-voltage relations of impacting plasma electrons Ie (Fs ) and escaping photoelectrons Iph (Fs ). The inferred relations are compared to analytic relationships in order to quantify the effects of the spacecraft geometry, the ambient magnetic field B0 and the electron temperature Te . We found that the complex geometry has a weak effect on the inferred currents, while the presence of B0 tends to decrease their values. Providing that the photoemission saturation current density Jph0 is known, a relation between Fs and the plasma density Ne can be derived by using the current balance. Since Jph0 is critical to this process, simultaneous measurements of Ne from Z-mode observations in the plasmapause, and data on the potential difference Fs - Fp between the spacecraft and an electric probe (p) are used in order to reverse the process. A value Jph0 ~ = 32 µAm-2 is estimated, close to laboratory tests, but less than typical measurements in space. Using this value, Ne and Fs can be derived systematically from electric field measurements without any additional calculation. These values are needed for correcting the distributions of low-energy ions measured by the Hyperboloid experiment on Interball-2. The effects of the potential structure on ion trajectories reaching Hyperboloid are discussed quantitatively in a companion paper.Key words. Space plasma physics (charged particle motion and acceleration; numerical simulation studies; spacecraft sheaths, wakes, charging)
6
Papavasileiou, Theodora, Odysseas Kosmas e Ioannis Sinatkas. "Simulations of Neutrino and Gamma-Ray Production from Relativistic Black-Hole Microquasar Jets". Galaxies 9, n. 3 (13 settembre 2021): 67. http://dx.doi.org/10.3390/galaxies9030067.
Abstract (sommario):
Recently, microquasar jets have aroused the interest of many researchers focusing on the astrophysical plasma outflows and various jet ejections. In this work, we concentrate on the investigation of electromagnetic radiation and particle emissions from the jets of stellar black hole binary systems characterized by the hadronic content in their jets. Such emissions are reliably described within the context of relativistic magneto-hydrodynamics. Our model calculations are based on the Fermi acceleration mechanism through which the primary particles (mainly protons and electrons) of the jet are accelerated. As a result, a small portion of thermal protons of the jet acquire relativistic energies, through shock-waves generated into the jet plasma. From the inelastic collisions of fast (non-thermal) protons with the thermal (cold) ones, secondary charged and neutral particles (pions, kaons, muons, η-particles, etc.) are created, as well as electromagnetic radiation from the radio wavelength band to X-rays and even very high energy gamma-rays. One of our main goals is, through the appropriate solution of the transport equation and taking into account the various mechanisms that cause energy losses to the particles, to study the secondary particle concentrations within hadronic astrophysical jets. After assessing the suitability and sensitivity of the derived (for this purpose) algorithms on the Galactic MQs SS 433 and Cyg X-1, as a concrete extragalactic binary system, we examine the LMC X-1 located in the Large Magellanic Cloud, a satellite galaxy of our Milky Way Galaxy. It is worth mentioning that, for the companion O star (and its extended nebula structure) of the LMC X-1 system, new observations using spectroscopic data from VLT/UVES have been published a few years ago.
7
Sridhar, Navin, e Brian D. Metzger. "Radio Nebulae from Hyperaccreting X-Ray Binaries as Common-envelope Precursors and Persistent Counterparts of Fast Radio Bursts". Astrophysical Journal 937, n. 1 (1 settembre 2022): 5. http://dx.doi.org/10.3847/1538-4357/ac8a4a.
Abstract (sommario):
Abstract Roche lobe overflow from a donor star onto a black hole or neutron star binary companion can evolve to a phase of unstable runaway mass transfer, lasting as short as hundreds of orbits (≲102 yr for a giant donor) and eventually culminating in a common-envelope event. The highly super-Eddington accretion rates achieved during this brief phase ( M ̇ ≳ 10 5 M ̇ Edd ) are accompanied by intense mass loss in disk winds, analogous to but even more extreme than ultraluminous X-ray (ULX) sources in the nearby universe. Also in analogy with the observed ULX, this expanding outflow will inflate an energetic “bubble” of plasma into the circumbinary medium. Embedded within this bubble is a nebula of relativistic electrons heated at the termination shock of the faster v ≳ 0.1c wind/jet from the inner accretion flow. We present a time-dependent, one-zone model for the synchrotron radio emission and other observable properties of such ULX “hypernebulae.” If ULX jets are sources of repeating fast radio bursts (FRB), as recently proposed, such hypernebulae could generate persistent radio emission and contribute large and time-variable rotation measure to the bursts, consistent with those seen from FRB 20121102 and FRB 20190520B. ULX hypernebulae can be discovered independently of an FRB association in radio surveys, such as VLASS, as off-nuclear point sources whose fluxes can evolve significantly on timescales as short as years, possibly presaging energetic transients from common-envelope mergers.
8
Martin-Solis, Jose Ramon, Jose Angel Mier, Michael Lehnen e Alberto Loarte. "Formation and termination of runaway beams during vertical displacement events in tokamak disruptions". Nuclear Fusion, 2 aprile 2022. http://dx.doi.org/10.1088/1741-4326/ac637b.
Abstract (sommario):
Abstract A simple 0-D model which mimics the plasma surrounded by the conducting structures [D.I. Kiramov, B.N. Breizman, Physics of Plasmas 24, 100702 (2017)] and including self-consistently the vertical plasma motion and the generation of runaway electrons during the disruption is used for an assessment of the effect of vertical displacement events on the runaway current formation and termination. The total plasma current and runaway current at the time the plasma hits the wall is estimated and the effect of injecting impurities into the plasma is evaluated. In the case of ITER, with a highly conducting wall, although the total plasma current when the plasma touches the wall is the same for any number of injected impurities, however the fraction of the plasma current carried by runaway electrons can significantly decrease for large enough amounts of impurities. The plasma velocity is larger and the time when the plasma hits the wall shorter for lower runaway currents, which are obtained when larger amounts of impurities are injected. When the plasma reaches the wall, the scraping-off of the runaway beam occurs and the current is terminated. During this phase, the plasma vertical displacement velocity and electric field can substantially increase leading to the deposition of a noticeable amount of energy on the runaway electrons (~ hundreds of MJ). It is found that an early second impurity injection reduces somewhat the amount of energy deposited by the runaways. Also larger temperatures of the companion plasma during the scraping-off might be efficient in reducing the power fluxes due to the runaways onto the PFCs. The plasma reaches the qa = 2 limit before the runaway electron current is terminated and by that time the amount of energy deposited on the runaway electrons can be substantially lower than that expected until the beam is fully terminated. Negligible additional conversion of magnetic into runaway kinetic energy is predicted during the runaway deconfinement following the large magnetic fluctuations after qa = 2 is crossed for characteristic deconfinement times lower than 0.1 ms which is a characteristic timescale for ideal MHD instabilities to develop.
9
Taunay, Pierre-Yves, Christopher Wordingham e Edgar Choueiri. "Physics of Thermionic, Orificed Hollow Cathodes. Part 1: Theory and Experimental Validation". Plasma Sources Science and Technology, 10 marzo 2022. http://dx.doi.org/10.1088/1361-6595/ac5c63.
Abstract (sommario):
Abstract A model aimed at illuminating the physics of thermionic, orificed hollow cathodes is developed and validated with experimental data. The model is intended to describe the variation of total (neutrals, ions, and electrons) static pressure with controllable parameters. That pressure must be properly evaluated because it influences important plasma parameters in the cathode such as the attachment length and the electron temperature, which directly impact the lifetime of thermionic inserts. The model, which combines a zero-dimensional approach to the conservation of energy and momentum for the combined plasma-neutral fluid and a charge-exchange-limited ambipolar diffusion model, allows for the computation of all plasma quantities, including the total fluid pressure. The model depends on the operating conditions (discharge current and mass flow rate), cathode geometry, and the gas species, along with two non-controllable parameters: the neutral gas temperature and the sheath potential. Total pressure data at up to 307 A of cathode discharge current were obtained experimentally and were used, along with data from the literature, to validate the model. Good agreement is obtained for all quantities. The model is used in a companion paper to clarify the role of magnetic and gasdynamic pressure in the scaling of total pressure, to derive scaling laws applicable to thermionic, orificed hollow cathodes, and to propose novel cathode design rules.
Tesi sul tema "Electrons découplés companion plasma":
1
Sridhar, Sundaresan. "Study of tokamak plasma disruptions and runaway electrons in a metallic environment". Electronic Thesis or Diss., Aix-Marseille, 2020. http://www.theses.fr/2020AIXM0313.
Abstract (sommario):
Les dispositifs de fusion de type tokamaks ont atteint des performances proches de celles nécessaires à réacteur industriel de fusion et les disruptions sont des événements majeurs dans lesquels l'énergie du plasma est perdue en un très court instant. Electrons découplés (RE), de par leur énergie (quelques 10ème\,MeV), peuvent endommager des composants internes du tokamak. La stratégie actuelle consiste à éviter la génération de RE à l’aide d’une injection massive de matière (MMI). Si leur génération ne peut pas être évitée, une 2ème MMI sera utilisée pour atténuer le faisceau d’électrons découplés. Après la 1ère MMI, un plasma de fond dense et froid d'impuretés MMI est formé et le 2ème MMI visant à atténuer l'emballement du faisceau d'électrons peut être inefficace dans ce plasma de fond, comme observé dans le tokamak JET. Comprendre la physique de l'interaction entre le faisceau d'électrons découplés et le 2ème MMI en présence du plasma de fond froid sera au centre de cette thèseTokamaks are the devices currently closest to achieve nuclear fusion power and disruptions are unfavorable events in which the plasma energy is lost in a very short timescale causing damage to tokamak structures. RE beams are one of the consequence of disruptions and they carry the risk of in-vessel component damage. Thus, the prevention and control of the RE are of prime importance. The current strategy for runaway electrons is to avoid their generation by a massive material injection (MMI). If their generation cannot be avoided, a 2nd MMI will be used to mitigate the generated RE beam. After the 1st MMI to prevent RE generation, a background plasma of 1st MMI impurities is formed which make the second MMI inefficient to mitigate RE beams inefficient, as observed in the JET tokamak. In this thesis, the physics of the interaction between the RE beam and the mitigation MMI in the presence of a cold background plasma is studied
2
Sommariva, Cristian. "Test particles dynamics in 3D non-linear magnetohydrodynamics simulations and application to runaway electron formation in tokamak disruptions". Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0512/document.
Abstract (sommario):
La thèse étudie la dynamique des Electrons Découplés (DE) dans une disruption plasma déclenchée par injection massive de gaz dans le tokamak JET et simulée par le code JOREK. Cette investigation est permise par l’implémentation d’un module de suivi des particules tests relativistes dans JOREK. L’étude montre que les électrons peuvent ‘survivre’dans le chaos magnétique caractérisant la phase dite de ‘Disjonction Thermique’ (DT) de cette disruption (simulée) grâce à la reformation des surfaces magnétiques fermées. Deuxièmement, l’accélération des électrons causée par les champs électriques dus aux fluctuations magnétohydrodynamiques (MHD) pendant la DT est analysée. Cela montre que les électrons peuvent être accélérés par ces champs et devenir DE, après reconfinement, pendant la phase dite de ‘Disjonction de Courant’. Une étude préliminaire sur les dépendances entre le courant des DE et l’activité MHD dans les expériences de disruption du tokamak ASDEX Upgrade est également reportéeIn view of better understanding Runaway Electron (RE) generation processes during tokamak disruptions, this work investigates test electron dynamics during a JET disruption simulated with the JOREK code. For this purpose, a JOREK module computing relativistic test particle orbits in the simulated fields has been developed and tested. The study shows that a significant fraction of pre-disruption thermal electrons remain confined in spite of the magnetic chaos characterizing the Thermal Quench (TQ) phase. This finding, which is related to the prompt reformation of closed flux surfaces after the TQ, supports the possibility of the so-called “hot tail” RE generation mechanism. In addition, it is found that electrons may be significantly accelerated during the TQ due to the presence of strong local electric field (E) fluctuations related to magnetohydrodynamic (MHD) activity. This phenomenon, which has virtually been ignored so far, may play an important role in RE generation. In connection to this modelling work, an experimental study on ASDEX Upgrade disruptions has been performed, suggesting that strong MHD activity reduces RE production
3
Sommariva, Cristian. "Test particles dynamics in 3D non-linear magnetohydrodynamics simulations and application to runaway electron formation in tokamak disruptions". Electronic Thesis or Diss., Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0512.
Abstract (sommario):
La thèse étudie la dynamique des Electrons Découplés (DE) dans une disruption plasma déclenchée par injection massive de gaz dans le tokamak JET et simulée par le code JOREK. Cette investigation est permise par l’implémentation d’un module de suivi des particules tests relativistes dans JOREK. L’étude montre que les électrons peuvent ‘survivre’dans le chaos magnétique caractérisant la phase dite de ‘Disjonction Thermique’ (DT) de cette disruption (simulée) grâce à la reformation des surfaces magnétiques fermées. Deuxièmement, l’accélération des électrons causée par les champs électriques dus aux fluctuations magnétohydrodynamiques (MHD) pendant la DT est analysée. Cela montre que les électrons peuvent être accélérés par ces champs et devenir DE, après reconfinement, pendant la phase dite de ‘Disjonction de Courant’. Une étude préliminaire sur les dépendances entre le courant des DE et l’activité MHD dans les expériences de disruption du tokamak ASDEX Upgrade est également reportéeIn view of better understanding Runaway Electron (RE) generation processes during tokamak disruptions, this work investigates test electron dynamics during a JET disruption simulated with the JOREK code. For this purpose, a JOREK module computing relativistic test particle orbits in the simulated fields has been developed and tested. The study shows that a significant fraction of pre-disruption thermal electrons remain confined in spite of the magnetic chaos characterizing the Thermal Quench (TQ) phase. This finding, which is related to the prompt reformation of closed flux surfaces after the TQ, supports the possibility of the so-called “hot tail” RE generation mechanism. In addition, it is found that electrons may be significantly accelerated during the TQ due to the presence of strong local electric field (E) fluctuations related to magnetohydrodynamic (MHD) activity. This phenomenon, which has virtually been ignored so far, may play an important role in RE generation. In connection to this modelling work, an experimental study on ASDEX Upgrade disruptions has been performed, suggesting that strong MHD activity reduces RE production