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Articles de revues sur le sujet « Runaway Electron »

Auteur : Grafiati

Publié le 9 mars 2023

Mis à jour le 11 mars 2023

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1

Breizman, B. N., et D. I. Kiramov. « Marginal stability constraint on runaway electron distribution ». Physics of Plasmas 30, n^o 2 (février 2023) : 022301. http://dx.doi.org/10.1063/5.0130558.

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High-frequency kinetic instabilities of the strongly anisotropic runaway electrons (RE) can enhance the pitch-angle scattering of the runaways significantly. This wave-induced scattering can easily prevail over runaway scattering on high-Z impurities. In a steady state, collisional damping balances the kinetic drive of the unstable waves, keeping the RE distribution function at marginal stability. The marginal stability constraint limits the achievable RE densities and the shape of the RE distribution function. In this study, we consider whistler and compressional Alfvén waves as the primary source of enhanced elastic scattering of the runaways. By balancing the anomalous Doppler resonance drive with the collisional wave damping, we find the RE distribution function in the ultra-relativistic range of the phase space. We also derive an expression for the spectral energy density of the waves. We show that the power needed to compensate for the wave dissipation is negligible compared to the work of the electric field. The latter is in balance with the synchrotron losses of the runaway electrons.

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Vlainic, Milos, Ondrej Ficker, Jan Mlynar et Eva Macusova. « Experimental Runaway Electron Current Estimation in COMPASS Tokamak ». Atoms 7, n^o 1 (16 janvier 2019) : 12. http://dx.doi.org/10.3390/atoms7010012.

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Runaway electrons present a potential threat to the safe operation of future nuclear fusion large facilities based on the tokamak principle (e.g., ITER). The article presents an implementation of runaway electron current estimations at COMPASS tokamak. The method uses a theoretical method developed by Fujita et al., with the difference in using experimental measurements from EFIT and Thomson scattering. The procedure was explained on the COMPASS discharge number 7298, which has a significant runaway electron population. Here, it was found that at least 4 kA of the plasma current is driven by the runaway electrons. Next, the method aws used on the set of plasma discharges with the variable electron plasma density. The difference in the plasma current was explained by runaway electrons, and their current was estimated using the aforementioned method. The experimental results are compared with the theory and simulation. The comparison presented some disagreements, showing the possible direction for the code development. Additional application on runaway electron energy limit is also addressed.

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3

YANG, JIN-WEI, YI-PO ZHANG, XU LI, XIAN-YING SONG, GUO-LIANG YUAN, MIN LIAO, LI-QUN HU, SHI-YAO LIN et QING-WEI YANG. « Suppression of runaway electrons during electron cyclotron resonance heating on HL-2A tokamak ». Journal of Plasma Physics 76, n^o 1 (10 septembre 2009) : 75–85. http://dx.doi.org/10.1017/s0022377809990250.

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AbstractThe statistical analysis of heating effect and the cross-correlation analysis of both electron temperature and loop voltage have been done during electron cyclotron resonance heating (ECRH). The behavior of runaway electrons in the flat-top phase during ECRH are analyzed using experimental data. It is shown that the runaway population is indeed suppressed or even quenched when the toroidal electric field ET is reduced below the threshold electric field Eth by high-power and long-duration ECRH. The physical mechanism of runaway suppression is explored by the resonant interaction between the electron cyclotron waves and the energetic runaway electrons.

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Pankratov, Igor M., et Volodymyr Y. Bochko. « Nonlinear Cone Model for Investigation of Runaway Electron Synchrotron Radiation Spot Shape ». 3, n^o 3 (28 septembre 2021) : 18–24. http://dx.doi.org/10.26565/2312-4334-2021-3-02.

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The runaway electron event is the fundamental physical phenomenon and tokamak is the most advanced conception of the plasma magnetic confinement. The energy of disruption generated runaway electrons can reach as high as tens of mega-electron-volt and they can cause a catastrophic damage of plasma-facing-component surfaces in large tokamaks and International Thermonuclear Experimental Reactor (ITER). Due to its importance, this phenomenon is being actively studied both theoretically and experimentally in leading thermonuclear fusion centers. Thus, effective monitoring of the runaway electrons is an important task. The synchrotron radiation diagnostic allows direct observation of such runaway electrons and an analysis of their parameters and promotes the safety operation of present-day large tokamaks and future ITER. In 1990 such diagnostic had demonstrated its effectiveness on the TEXTOR (Tokamak Experiment for Technology Oriented Research, Germany) tokamak for investigation of runaway electrons beam size, position, number, and maximum energy. Now this diagnostic is installed practically on all the present-day’s tokamaks. The parameter v┴/|v||| strongly influences on the runaway electron synchrotron radiation behavior (v|| is the longitudinal velocity, v┴ is the transverse velocity with respect to the magnetic field B). The paper is devoted to the theoretical investigation of runaway electron synchrotron radiation spot shape when this parameter is not small that corresponds to present-day tokamak experiments. The features of the relativistic electron motion in a tokamak are taken into account. The influence of the detector position on runaway electron synchrotron radiation data is discussed. Analysis carried out in the frame of the nonlinear cone model. In this model, the ultrarelativistic electrons emit radiation in the direction of their velocity v→ and the velocity vector runs along the surface of a cone whose axis is parallel to the magnetic field B. The case of the small parameter v┴/|v||| (v┴/|v|||<<1, linear cone model) was considered in the paper: Plasma Phys. Rep. 22, 535 (1996) and these theoretical results are used for experimental data analysis.

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5

Lisenkov, V. V., Yu I. Mamontov et I. N. Tikhonov. « Numerical investigation of a high-pressure gas medium preionization by runaway electrons ». Journal of Physics : Conference Series 2064, n^o 1 (1 novembre 2021) : 012021. http://dx.doi.org/10.1088/1742-6596/2064/1/012021.

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Abstract A comparative simulation of the generation and acceleration of runaway electrons in the discharge gap during the initiation of the discharge by nanosecond and subnanosecond pulses is carried out. We used a numerical model based on the PIC-MCC method. Calculations were carried out for N2 6 atm pressure. Numerical simulation of a formation process of the electron avalanche initiated by an electron field-emitted from the top of the cathode microspike was carried out taking into account the motion of each electron in the avalanche. Characteristic runaway electron trajectories, runaway electron energy gained during the motion through the discharge gap, times required for runaway electrons to reach the anode were calculated. We compared our results with calculations using well-known differential equation of electron acceleration using braking force in Bethe approximation. We solved this equation also for braking force based on real (experimental) ionization cross section. The reasons for the discrepancy in the calculation results are discussed.

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6

KOMIRENKO, S. M., K. W. KIM, V. A. KOCHELAP et M. A. STROSCIO. « HIGH-FIELD ELECTRON TRANSPORT CONTROLLED BY OPTICAL PHONON EMISSION IN NITRIDES ». International Journal of High Speed Electronics and Systems 12, n^o 04 (décembre 2002) : 1057–81. http://dx.doi.org/10.1142/s0129156402001927.

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We have investigated the problem of electron runaway at strong electric fields in polar semiconductors focusing on the nanoscale nitride-based heterostructures. A transport model which takes into account the main features of electrons injected in short devices under high electric fields is developed. The electron distribution as a function of the electron momenta and coordinate is analyzed. We have determined the critical field for the runaway regime and investigated this regime in detail. The electron velocity distribution over the device is studied at different fields. We have applied the model to the group-III nitrides: InN, GaN and AlN. For these materials, the basic parameters and characteristics of the high-field electron transport are obtained. We have found that the transport in the nitrides is always dissipative. However, in the runaway regime, energies and velocities of electrons increase with distance which results in average velocities higher than the peak velocity in bulk-like samples. We demonstrated that the runaway electrons are characterized by the extreme distribution function with the population inversion. A three-terminal heterostructure where the runaway effect can be detected and measured is proposed. We also have considered briefly different nitride-based small-feature-size devices where this effect can have an impact on the device performance.

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7

Cerovsky, J., O. Ficker, V. Svoboda, E. Macusova, J. Mlynar, J. Caloud, V. Weinzettl et M. Hron. « Progress in HXR diagnostics at GOLEM and COMPASS tokamaks ». Journal of Instrumentation 17, n^o 01 (1 janvier 2022) : C01033. http://dx.doi.org/10.1088/1748-0221/17/01/c01033.

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Abstract Scintillation detectors are widely used for hard X-ray spectroscopy and allow us to investigate the dynamics of runaway electrons in tokamaks. This diagnostic tool proved to be able to provide information about the energy or the number of runaway electrons. Presently it has been used for runaway studies at the GOLEM and the COMPASS tokamaks. The set of scintillation detectors used at both tokamaks was significantly extended and improved. Besides NaI(Tl) (2 × 2 inch) scintillation detectors, YAP(Ce) and CeBr3 were employed. The data acquisition system was accordingly improved and the data from scintillation detectors is collected with appropriate sampling rate (≈300 MHz) and sufficient bandwidth (≈100 MHz) to allow a pulse analysis. Up to five detectors can currently simultaneously monitor hard X-ray radiation at the GOLEM. The same scintillation detectors were also installed during the runaway electron campaign at the COMPASS tokamak. The aim of this contribution is to report progress in diagnostics of HXR radiation induced by runaway electrons at the GOLEM and the COMPASS tokamaks. The data collected during the 12th runaway electron campaign (2020) at COMPASS shows that count rates during typical low-density runaway electron discharges are in a range of hundreds of kHz and detected photon energies go up to 10 MeV (measured outside the tokamak hall). Acquired data from experimental campaigns from both machines will be discussed.

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8

Zubarev, Nikolay M., Olga V. Zubareva et Michael I. Yalandin. « Features of Electron Runaway in a Gas Diode with a Blade Cathode ». Electronics 11, n^o 17 (2 septembre 2022) : 2771. http://dx.doi.org/10.3390/electronics11172771.

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Conditions for electron runaway in a gas diode with a blade cathode providing a strongly inhomogeneous distribution of the electric field in the interelectrode gap have been studied theoretically. It has been demonstrated that the character of electron runaway differs qualitatively for cathodes with a different rounding radius of the edges. In the case of a relatively large edge radius (tens of microns or more), the conditions for the transition of electrons to the runaway mode are local in nature: they are determined by the field distribution in the immediate vicinity of the cathode where the electrons originate from. Here, the relative contribution of the braking force acting on electrons in a dense gas reaches a maximum. This behavior is generally similar to the behavior of electrons in a uniform field. For a cathode with a highly sharpened edge, the relative contribution of the braking force is maximum in the near-anode region. As a consequence, the runaway condition acquires a nonlocal character: it is determined by the electron dynamics in the entire interelectrode gap.

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9

Zhang, Cheng, Jianwei Gu, Ruexue Wang, Hao Ma, Ping Yan et Tao Shao. « Simulation of runaway electron inception and breakdown in nanosecond pulse gas discharges ». Laser and Particle Beams 34, n^o 1 (23 novembre 2015) : 43–52. http://dx.doi.org/10.1017/s0263034615000944.

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AbstractNanosecond pulse discharges can provide high reduced electric field for exciting high-energy electrons, and the ultrafast rising time of the applied pulse can effectively suppress the generation of spark streamer and produce homogeneous discharges preionized by runaway electrons in atmospheric-pressure air. In this paper, the electrostatic field in a tube-plate electrodes gap is calculated using a calculation software. Furthermore, a simple physical model of nanosecond pulse discharges is established to investigate the behavior of the runaway electrons during the nanosecond pulse discharges with a rise time of 1.6 ns and a full-width at half-maximum of 3–5 ns in air. The physical model is coded by a numerical software, and then the runaway electrons and electron avalanche are investigated under different conditions. The simulated results show that the applied voltage, voltage polarity, and gas pressure can significantly affect the formation of the avalanche and the behavior of the runaway electrons. The inception time of runaway breakdown decreases when the applied voltage increases. In addition, the threshold voltage of runaway breakdown has a minimum value (10 kPa) with the variation of gas pressure.PACS: 52.80.-s

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10

Babich, Leonid P. « Relativistic runaway electron avalanche ». Uspekhi Fizicheskih Nauk 190, n^o 12 (avril 2020) : 1261–92. http://dx.doi.org/10.3367/ufnr.2020.04.038747.

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11

Carnevale, D., M. Ariola, G. Artaserse, F. Bagnato, W. Bin, L. Boncagni, T. Bolzonella et al. « Runaway electron beam control ». Plasma Physics and Controlled Fusion 61, n^o 1 (27 novembre 2018) : 014036. http://dx.doi.org/10.1088/1361-6587/aaef53.

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12

Shao, Tao, Victor F. Tarasenko, Cheng Zhang, Evgeni KH Baksht, Ping Yan et Yuliya V. Shut'Ko. « Repetitive nanosecond-pulse discharge in a highly nonuniform electric field in atmospheric air : X-ray emission and runaway electron generation ». Laser and Particle Beams 30, n^o 3 (25 mai 2012) : 369–78. http://dx.doi.org/10.1017/s0263034612000201.

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AbstractRepetitive nanosecond-pulse discharge with a highly inhomogeneous electric field was investigated in air at atmospheric pressure. Three repetitive nanosecond generators were used, and the rise times of the voltage pulses were 15, 1, and 0.2 ns, respectively. Under different experimental conditions, X-rays and runaway electron beams were directly measured using various setups. The variables affecting X-rays and runaway electrons, including gap distance, pulse repetition frequency, anode geometry, and material, were investigated. It was shown that it was significantly easier to record the X-rays than the runaway electrons in the repetitive nanosecond-pulse discharge. It was confirmed that a volume diffuse discharge was attributed to the generation of runaway electrons and the corresponding X-rays.

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13

Белоплотов, Д. В., В. Ф. Тарасенко, Д. А. Сорокин et В. А. Шкляев. « Формирование двух импульсов тока пучка убегающих электронов ». Журнал технической физики 91, n^o 4 (2021) : 589. http://dx.doi.org/10.21883/jtf.2021.04.50621.292-20.

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The conditions for the formation of two current pulses of runaway electron beams during the breakdown of a point-to-plane and tube-to-plane gaps in high-pressure air, nitrogen, and helium are studied. It has been shown experimentally that, depending on a pressure and kind of gas, a rise time of voltage pulse with an amplitude of tens of kilovolts, three modes of generation of runaway electron beams are observed. In the first mode, a single current pulse of runaway electron beam is observed at the maximum voltage across the gap, when a streamer appears in the vicinity of the pointed electrode (cathode). Its duration is ≈100 ps. In the second mode, two current pulses of runaway electron beams are observed at a lower pressure. The first pulse is generated as in the first mode. The second pulse is generated after the gap is bridged by the streamer (the first ionization wave). The electron energy in the second pulse is significantly less than in the first one, but the duration and amplitude of second current pulse under optimal conditions are greater. The third mode is implemented at lower pressures than in the second one. The generation of runaway electrons continues after the first pulse without a pause in the quasi-stationary stage. The total current pulse duration is hundreds of picoseconds.

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14

Kulkov, S., M. Marcisovsky, P. Svihra, M. Tunkl, M. van Beuzekom, J. Caloud, J. Cerovsky et al. « Detection of runaway electrons at the COMPASS tokamak using a Timepix3-based semiconductor detector ». Journal of Instrumentation 17, n^o 02 (1 février 2022) : P02030. http://dx.doi.org/10.1088/1748-0221/17/02/p02030.

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Abstract Runaway electrons are considered dangerous for the integrity of tokamak vacuum vessels. To secure the success of the future tokamak-based machines, reliable diagnostics and mitigation strategies are necessary. The COMPASS tokamak supported the research of runaway electron physics via regular experimental campaigns. During the last two experimental campaigns dedicated to runaway electrons, a semiconductor detector with a Timepix3 readout chip, Si sensor, and the SPIDR readout system was tested. Time evolution signals, energy measurements, and sensor snapshots collected with the Timepix3-based detector are presented.

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15

Farnik, Michal, Jakub Urban, Jaromir Zajac, Ondrej Bogar, Ondrej Ficker, Eva Macusova, Jan Mlynar et al. « Runaway electron diagnostics for the COMPASS tokamak using EC emission ». EPJ Web of Conferences 203 (2019) : 03006. http://dx.doi.org/10.1051/epjconf/201920303006.

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An electron cyclotron emission (ECE) diagnostic of suprathermal electrons was utilised for runaway electron (RE) experiments purposes in the COMPASS tokamak. Our vertical ECE (V-ECE) system consists of a 16-channel heterodyne radiometer and an E-band horn antenna with a 76.5-88 GHz frequency range front-end. Simulations used for the design of the diagnostic showed a possibility of detecting the emission of low-energy (50-140 keV) runaway electrons. We realized measurements with both extraordinary (X-) and ordinary (O-) mode linear polarizations. The amplitudes of the X-mode and O-mode signals are similar, which can be explained by depolarised reflected radiation. V-ECE measurements in low-density flattop discharges and in discharges with massive gas injections of high-Z elements show correlations with other RE diagnostics. Our results are in the agreement with the principles of the primary runaway generation mechanisms.

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Tarasenko, Victor, Dmitriy Beloplotov, Dmitriy Sorokin et Evgeniy Baksht. « Modes of runaway electron beams during formation of diffuse discharges in air and nitrogen ». ADVANCES IN APPLIED PHYSICS 9, n^o 3 (3 août 2021) : 202–15. http://dx.doi.org/10.51368/2307-4469-2021-9-3-202-215.

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Investigations of the generation of runaway electron beams (REs) and the for-mation of diffuse discharges during breakdown of gaps with a cathode, which has a small radius of curvature, have been carried out. In air and nitrogen at elevated pressure, based on the registration and analysis of the characteristics of radiation from discharge, as well as parameters of the RE beam current and dynamic dis-placement current, it is shown that, depending on the conditions (E/N, gas type and its pressure, design and material of the cathode, amplitude and front of the voltage pulse), diffe- rent modes of generation of runaway electron beams are realized. It was found that the ratio of the velocity of the front of the ionization wave (streamer) and the runaway electrons, as well as the design of the cathode and the delay time before the explosion of cathode microinhomogeneities, significantly affect the generation of runaway electrons. The conditions for the realization of various modes are de-termined; oscillograms of the beam current pulses and photographs of the glow of the gap are presented.

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17

Canright, G. S., et G. D. Mahan. « Hot electrons in one dimension : Electron velocity runaway ». Physical Review B 36, n^o 5 (15 août 1987) : 2870–72. http://dx.doi.org/10.1103/physrevb.36.2870.

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18

Guo, L., H. W. Zhang et H. C. Wu. « High-frequency radio-wave emission by coherent transition radiation of runaway electrons produced by lightning stepped leaders ». Physics of Plasmas 29, n^o 9 (septembre 2022) : 093102. http://dx.doi.org/10.1063/5.0102132.

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Lightning can produce multiband radio waves and high-energy radiations. Some of them are associated with the formation of lightning leaders. However, their generation mechanisms are not fully understood yet. Based on the understanding of thermal runaway electrons generated at the leader tip, we propose transition radiation of these runaway electrons as an alternative mechanism for producing very-high-frequency radio signals. Transition radiations are induced when runaway electrons cross the interfaces between lightning coronas and the air. By the use of estimated parameters of electron beams emerging from the leader tips, we calculate their coherent transition radiation and find that the energy spectra and radiation powers are consistent with some detection results from stepped leaders and even narrow bipolar events. Moreover, our model also predicts strong THz radiation during the stepped-leader formation. As a standard diagnosis technique of electron bunches, the proposed coherent transition radiation here may be able to reconstruct the actual properties of electron beams in the leader tips, which remains an open question.

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Babich, Leonid, et Evgeniĭ Bochkov. « Electron runaway rate in air ». Journal of Physics D : Applied Physics 54, n^o 46 (9 septembre 2021) : 465205. http://dx.doi.org/10.1088/1361-6463/ac1886.

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20

Wongrach, K., K. H. Finken, S. S. Abdullaev, O. Willi, L. Zeng et Y. Xu. « Runaway electron studies in TEXTOR ». Nuclear Fusion 55, n^o 5 (16 avril 2015) : 053008. http://dx.doi.org/10.1088/0029-5515/55/5/053008.

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Esposito, B., L. Boncagni, P. Buratti, D. Carnevale, F. Causa, M. Gospodarczyk, JR Martin-Solis et al. « Runaway electron generation and control ». Plasma Physics and Controlled Fusion 59, n^o 1 (16 novembre 2016) : 014044. http://dx.doi.org/10.1088/0741-3335/59/1/014044.

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DMITRIEV, ALEXANDER, VALENTIN KACHOROVSKI, MICHAEL S. SHUR et MICHAEL STROSCIO. « ELECTRON DRIFT VELOCITY OF THE TWO-DIMENSIONAL ELECTRON GAS IN COMPOUND SEMICONDUCTORS ». International Journal of High Speed Electronics and Systems 10, n^o 01 (mars 2000) : 103–10. http://dx.doi.org/10.1142/s0129156400000131.

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We show that, as a consequence of an enhanced electron runaway for two-dimensional (2D) electrons, the peak electron drift velocity and peak electric field in compound semiconductors are smaller than in bulk semiconductors. This prediction agrees with the results of Monte-Carlo simulations for the 2D electrons at a GaAs/GaAlAs heterointerface and with the measured peak velocities in InGaAs/InAlAs quantum wells.

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23

Kurzan, B., et K. H. Steuer. « Runaway electrons in a tokamak : A free-electron maser ». Physical Review E 55, n^o 4 (1 avril 1997) : 4608–16. http://dx.doi.org/10.1103/physreve.55.4608.

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Kurzan, B., K. H. Steuer et W. Suttrop. « Runaway electrons in a Tokamak : A free-electron maser ». Review of Scientific Instruments 68, n^o 1 (janvier 1997) : 423–26. http://dx.doi.org/10.1063/1.1148062.

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Mesyats, Gennady, Vladislav Rostov, Konstantin Sharypov, Valery Shpak, Sergey Shunailov, Michael Yalandin et Nikolay Zubarev. « Emission Features and Structure of an Electron Beam versus Gas Pressure and Magnetic Field in a Cold-Cathode Coaxial Diode ». Electronics 11, n^o 2 (13 janvier 2022) : 248. http://dx.doi.org/10.3390/electronics11020248.

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The structure of the emission surface of a cold tubular cathode and electron beam was investigated as a function of the magnetic field in the coaxial diode of the high-current accelerator. The runaway mode of magnetized electrons in atmospheric air enabled registering the instantaneous structure of activated field-emission centers at the cathode edge. The region of air pressure (about 3 Torr) was determined experimentally and via analysis, where the explosive emission mechanism of the appearance of fast electrons with energies above 100 keV is replaced by the runaway electrons in a gas.

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Guo, Zehua, Xian-Zhu Tang et Christopher J. McDevitt. « Models of primary runaway electron distribution in the runaway vortex regime ». Physics of Plasmas 24, n^o 11 (novembre 2017) : 112508. http://dx.doi.org/10.1063/1.5006917.

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Grasso, Daniela, Dario Borgogno, Lovepreet Singh et Fabio Subba. « Stability of a weakly collisional plasma with runaway electrons ». Journal of Physics : Conference Series 2397, n^o 1 (1 décembre 2022) : 012004. http://dx.doi.org/10.1088/1742-6596/2397/1/012004.

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Abstract We investigate the problem of the tearing stability of a post-disruption weakly collisional plasma where the current is completely carried by runaway electrons. We adopt here a two fluid model which takes into account also ion sound Larmor radius and electron inertia effects in the description of the reconnection process. In the past, it has been demonstrated in [Helander et al. Phys. Plasmas 14, 12, (2007)] that in the purely resistive regime the presence of runaway electrons in plasma has a significant effect on the saturated magnetic island width. In particular, runaway electrons generated during disruption can cause an increase of 50% in the saturated magnetic island width with respect to the case with no runaway electrons. These results were obtained adopting a periodic equilibrium magnetic field that limited the analysis to small size saturated magnetic islands. Here we present our results to overcome this limitation adopting a non-periodic Harris’ type equilibrium magnetic field. Preliminary results on the effects of the ion sound Larmor radius effects will also be presented.

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Scudder, Jack D. « The Origin of Persistently Nonthermal Solar Wind Electrons : the Steady Electron Runaway Model's Demonstration of Dreicer Bifurcation using Measured E∥ and Ion–Electron Coulomb Drag ». Astrophysical Journal 944, n^o 2 (1 février 2023) : 133. http://dx.doi.org/10.3847/1538-4357/acae26.

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Abstract The Steady Electron Runaway Model (SERM) develops the hypothesis that the solar wind’s observed ubiquitous nonthermal electron velocity distribution functions (eVDFs) are caused by Dreicer's velocity space bifurcation in the strong dimensionless E ∥ required by quasi-neutrality. SERM’s predicted partitions for the pressure and density are contrasted with appropriately adapted eVDF properties from the Wind 3DP experiment (1995–1998), based on in situ observations of E ∥ . The observed number fraction of electrons in runaway, δ 3DP, follows a thousandfold decline of Dreicer’s predicted fraction, δ, across the observed tenfold reduction of E ∥ , satisfying δ 3DP ≃ δ 0.89. SERM’s predictions are shown to reproduce the observed variations with E ∥ of the electron partial pressure and excess kurtosis,  e .  e and E ∥ are positively correlated across 4 yr, as expected by the SERM–Dreicer origin of the suprathermals. SERM quantitatively explains the observed 50 yr anticorrelation between δ 3DP and the partition slope temperature ratios. This documentation quantitatively establishes Coulomb runaway physics as the missing determinant of the ubiquitous nonthermal solar wind eVDF. Astrophysical plasmas, like stellar winds, are unavoidably inhomogeneous, requiring E ∥ to enforce quasi-neutrality. Between the stars E ∥ is expected to be sufficiently large that measurable runaway density fractions (0.1%–30%) will occur, producing widespread leptokurtic eVDFs. Using inhomogeneous two-fluid information, SERM predicts spatially dependent leptokurtic eVDF profiles consonant with Coulomb collisions and the fluid’s E ∥(r). SERM can also comment on its eVDFs’ consistency with Maxwellians presumed in the Spitzer–Härm closure. The solar wind profile shows the implied strong radial gradient of the plasma eVDF’s transformation from near thermal to strongly leptokurtic across 1.5–6 R ⊙.

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Bin, W., P. Buratti, A. Cardinali, C. Castaldo, F. Napoli et O. Tudisco. « Measurement of electromagnetic waves from runaway electrons ». Review of Scientific Instruments 93, n^o 9 (1 septembre 2022) : 093516. http://dx.doi.org/10.1063/5.0101650.

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Electromagnetic waves emitted during a tokamak discharge can be partially ascribed to coupling with plasma waves. In particular, in the presence of runaway electrons, the electromagnetic waves deliver information, otherwise inaccessible, about kinetic instabilities excited by the fast particles. Experiments aimed at studying radio frequency emissions from runaway electron scenarios during different stages of plasma discharge have been carried out at the Frascati Tokamak Upgrade. Frequencies in the range of lower hybrid and whistler waves have been explored, in the presence of relativistic electrons with different energies, ranging from a few to tens of MeV. A pronounced sensitivity of the radio frequency measurements in detecting driven instabilities is observed, providing the possibility to exploit this kind of technique as a monitor of the instability processes and for studies of the fast electron activity. In particular, in this work, we propose a simplified analysis of the frequency scaling of a specific family of kinetic instabilities arising at the lower hybrid frequency range during the current ramp-up stage. The study is performed with respect to the density profile and the wave vector coupling conditions and is aimed at obtaining a rough estimate of the most likely radial location of the interaction between the runaway electron beam and plasma waves at the emission times of the observed signals.

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30

Liu, Chang, Dylan P. Brennan, Allen H. Boozer et Amitava Bhattacharjee. « Adjoint method and runaway electron avalanche ». Plasma Physics and Controlled Fusion 59, n^o 2 (16 décembre 2016) : 024003. http://dx.doi.org/10.1088/1361-6587/59/2/024003.

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Mesyats, G. A., M. I. Yalandin, A. G. Reutova, K. A. Sharypov, V. G. Shpak et S. A. Shunailov. « Picosecond runaway electron beams in air ». Plasma Physics Reports 38, n^o 1 (janvier 2012) : 29–45. http://dx.doi.org/10.1134/s1063780x11110055.

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32

Hauff, T., et F. Jenko. « Runaway electron transport via tokamak microturbulence ». Physics of Plasmas 16, n^o 10 (octobre 2009) : 102308. http://dx.doi.org/10.1063/1.3243494.

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Kuznetsov, Yu K., R. M. O. Galvão, O. C. Usuriaga, S. I. Krasheninnikov, T. K. Soboleva, V. S. Tsypin, A. M. M. Fonseca, L. F. Ruchko et E. K. Sanada. « Recombinative plasma in electron runaway discharge ». Physics of Plasmas 12, n^o 7 (juillet 2005) : 072508. http://dx.doi.org/10.1063/1.1942498.

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Smith, H. M., T. Fehér, T. Fülöp, K. Gál et E. Verwichte. « Runaway electron generation in tokamak disruptions ». Plasma Physics and Controlled Fusion 51, n^o 12 (10 novembre 2009) : 124008. http://dx.doi.org/10.1088/0741-3335/51/12/124008.

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Boozer, Allen H. « Magnetic surface loss and electron runaway ». Plasma Physics and Controlled Fusion 61, n^o 2 (7 janvier 2019) : 024002. http://dx.doi.org/10.1088/1361-6587/aaf293.

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Oreshkin, E. V., S. A. Barengolts, V. I. Oreshkin et G. A. Mesyats. « Parameters of a runaway electron avalanche ». Physics of Plasmas 24, n^o 10 (octobre 2017) : 103505. http://dx.doi.org/10.1063/1.4990729.

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Besedin, N. T., et I. M. Pankratov. « Stability of a runaway electron beam ». Nuclear Fusion 26, n^o 6 (1 juin 1986) : 807–12. http://dx.doi.org/10.1088/0029-5515/26/6/009.

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Causa, F., M. Gospodarczyk, P. Buratti, D. Carnevale, R. De Angelis, B. Esposito, A. Grosso et al. « Runaway electron imaging spectrometry (REIS) system ». Review of Scientific Instruments 90, n^o 7 (juillet 2019) : 073501. http://dx.doi.org/10.1063/1.5061833.

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Bolt, H., A. Miyahara, M. Miyake et T. Yamamoto. « Simulation of tokamak runaway-electron events ». Journal of Nuclear Materials 151, n^o 1 (décembre 1987) : 48–54. http://dx.doi.org/10.1016/0022-3115(87)90054-7.

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Yuan, Shaohua, Nizar Naitlho, Roman Samulyak, Bernard Pégourié, Eric Nardon, Eric Hollmann, Paul Parks et Michael Lehnen. « Lagrangian particle simulation of hydrogen pellets and SPI into runaway electron beam in ITER ». Physics of Plasmas 29, n^o 10 (octobre 2022) : 103903. http://dx.doi.org/10.1063/5.0110388.

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Numerical studies of the ablation of pellets and shattered pellet injection (SPI) fragments into a runaway electron beam in ITER have been performed using a time-dependent pellet ablation code [Samulyak et al., Nucl. Fusion, 61(4), 046007 (2021)]. The code resolves detailed ablation physics near pellet fragments and large-scale expansion of ablated clouds. The study of a single-fragment ablation quantifies the influence of various factors, in particular, the impact ionization by runaway electrons and cross-field transport models, on the dynamics of ablated plasma and its penetration into the runaway beam. Simulations of SPI performed using different numbers of pellet fragments study the formation and evolution of the ablation clouds and their large-scale dynamics in ITER. The penetration depth of the ablation clouds is found to be of the order of 50 cm.

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41

Surkov, V. V., et M. Hayakawa. « Underlying mechanisms of transient luminous events : a review ». Annales Geophysicae 30, n^o 8 (17 août 2012) : 1185–212. http://dx.doi.org/10.5194/angeo-30-1185-2012.

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Abstract. Transient luminous events (TLEs) occasionally observed above a strong thunderstorm system have been the subject of a great deal of research during recent years. The main goal of this review is to introduce readers to recent theories of electrodynamics processes associated with TLEs. We examine the simplest versions of these theories in order to make their physics as transparent as possible. The study is begun with the conventional mechanism for air breakdown at stratospheric and mesospheric altitudes. An electron impact ionization and dissociative attachment to neutrals are discussed. A streamer size and mobility of electrons as a function of altitude in the atmosphere are estimated on the basis of similarity law. An alternative mechanism of air breakdown, runaway electron mechanism, is discussed. In this section we focus on a runaway breakdown field, characteristic length to increase avalanche of runaway electrons and on the role played by fast seed electrons in generation of the runaway breakdown. An effect of thunderclouds charge distribution on initiation of blue jets and gigantic jets is examined. A model in which the blue jet is treated as upward-propagating positive leader with a streamer zone/corona on the top is discussed. Sprite models based on streamer-like mechanism of air breakdown in the presence of atmospheric conductivity are reviewed. To analyze conditions for sprite generation, thunderstorm electric field arising just after positive cloud-to-ground stroke is compared with the thresholds for propagation of positively/negatively charged streamers and with runway breakdown. Our own estimate of tendril's length at the bottom of sprite is obtained to demonstrate that the runaway breakdown can trigger the streamer formation. In conclusion we discuss physical mechanisms of VLF (very low frequency) and ELF (extremely low frequency) phenomena associated with sprites.

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Kachlishvili, Z. S., et F. G. Chumburidze. « Transverse runaway of hot electrons and the electron-temperature approximation ». Journal of Experimental and Theoretical Physics 86, n^o 2 (février 1998) : 380–82. http://dx.doi.org/10.1134/1.558439.

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Mesyats, G. A., A. G. Reutova, K. A. Sharypov, V. G. Shpak, S. A. Shunailov et M. I. Yalandin. « On the observed energy of runaway electron beams in air ». Laser and Particle Beams 29, n^o 4 (décembre 2011) : 425–35. http://dx.doi.org/10.1017/s0263034611000541.

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AbstractExperiments with an air electrode gap have been performed where the current/charge of a picosecond beam of runaway electrons was measured over a wide range (up to four orders of magnitude) downstream of the absorbing foil filters. Measurements and calculations have made it possible to refer the beam current to the rise time of the accelerating voltage pulse to within picoseconds. It has been shown that, in contrast to a widespread belief, the runaway electron energies achieved are no greater than those corresponding to the mode of free acceleration of electrons in a nonstationary, highly nonuniform electric field induced by the cathode voltage. The experimental data agree with predictions of a numerical model that describes free acceleration of particles. It has been confirmed that the magnitude of the critical electric field that is necessary for electrons to go into the mode of continuous acceleration of electrons in atmospheric air corresponds to classical notions.

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Kozyrev, Andrey, Vasily Kozhevnikov et Natalia Semeniuk. « Why do Electrons with “Anomalous Energies” appear in High-Pressure Gas Discharges ? » EPJ Web of Conferences 167 (2018) : 01005. http://dx.doi.org/10.1051/epjconf/201816701005.

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Experimental studies connected with runaway electron beams generation convincingly shows the existence of electrons with energies above the maximum voltage applied to the discharge gap. Such electrons are also known as electrons with “anomalous energies”. We explain the presence of runaway electrons having so-called “anomalous energies” according to physical kinetics principles, namely, we describe the total ensemble of electrons with the distribution function. Its evolution obeys Boltzmann kinetic equation. The dynamics of self-consistent electromagnetic field is taken into the account by adding complete Maxwell’s equation set to the resulting system of equations. The electrodynamic mechanism of the interaction of electrons with a travelling-wave electric field is analyzed in details. It is responsible for the appearance of electrons with high energies in real discharges.

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Zhang Cheng, Ma Hao, Shao Tao, Xie Qing, Yang Wen-Jin et Yan Ping. « Runaway electron beams in nanosecond-pulse discharges ». Acta Physica Sinica 63, n^o 8 (2014) : 085208. http://dx.doi.org/10.7498/aps.63.085208.

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Novotny, L., J. Cerovsky, P. Dhyani, O. Ficker, M. Havranek, M. Hejtmanek, Z. Janoska et al. « Runaway electron diagnostics using silicon strip detector ». Journal of Instrumentation 15, n^o 07 (10 juillet 2020) : C07015. http://dx.doi.org/10.1088/1748-0221/15/07/c07015.

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England, A. C., G. L. Bell, R. H. Fowler, J. C. Glowienka, J. H. Harris, D. K. Lee, M. Murakami et al. « Runaway electron studies in the ATF torsatron ». Physics of Fluids B : Plasma Physics 3, n^o 7 (juillet 1991) : 1671–86. http://dx.doi.org/10.1063/1.859687.

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Smith, H. M., A. H. Boozer et P. Helander. « Passive runaway electron suppression in tokamak disruptions ». Physics of Plasmas 20, n^o 7 (juillet 2013) : 072505. http://dx.doi.org/10.1063/1.4813255.

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Celestin, Sebastien, et Victor P. Pasko. « Soft collisions in relativistic runaway electron avalanches ». Journal of Physics D : Applied Physics 43, n^o 31 (23 juillet 2010) : 315206. http://dx.doi.org/10.1088/0022-3727/43/31/315206.

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Oreshkin, E. V., S. A. Barengolts, S. A. Chaikovsky et V. I. Oreshkin. « Runaway electron beam in atmospheric pressure discharges ». Journal of Physics : Conference Series 653 (11 novembre 2015) : 012158. http://dx.doi.org/10.1088/1742-6596/653/1/012158.

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