Observation of two threshold fields for runaway-electron generation in tokamaks

Zhu, Xiang; Zeng, Long; Liang, Yun-Feng; Lin, Shiyao; Liu, Yong; Liu, Haiqing; Koslowski, H. R.; Eidietis, N. W.; Zhang, Jizong; Zhou, Ruijie; Zhao, Hailin; Ti, Ang; Qian, J.; Jie, Yinxian; Zhang, Shoubiao; Gao, Xiang

doi:10.1088/1741-4326/ab96f3

Cited by 14 publications

(9 citation statements)

References 34 publications

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“…Hard x-ray spectroscopy of hot plasma is one of the few methods that allow one to estimate the energy distribution of REs. The possibilities of RE diagnostics by the bremsstrahlung registration were demonstrated in measurements at small and medium size tokamaks Globus-M [7], HT-7 [8][9][10], FT-2 [11,12], J-TEXT [13,14], COMPASS [15] and TUMAN-3M [16]. In these experiments, the spectra of bremsstrahlung generated by the interaction of REs with the materials of the tokamak plasma facing components were measured.…”

Section: Introductionmentioning

confidence: 97%

Study of runaway electron dynamics at the ASDEX Upgrade tokamak during impurity injection using fast hard x-ray spectrometry

et al. 2021

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To study the runaway electron (RE) dynamics during plasma discharge and develop scenarios for disruption mitigation, a hard x-ray (HXR) spectrometric system has been developed and commissioned at the ASDEX Upgrade tokamak (AUG). The diagnostic system consists of two high-performance spectrometers based on LaBr3(Ce) scintillation detectors supplied with advanced electronics and analysis algorithms. These spectrometers view the AUG tokamak chamber quasi-radially at the equatorial plane. The measurements were carried out in the RE beam generation regimes by injecting argon into a deuterium plasma. In the interaction of a developed RE beam with a heavy gas target, powerful bremsstrahlung flux is induced, reaching energy close to 20 MeV. The electron energy distributions were reconstructed from the measured HXR spectra by deconvolution methods. The experimentally obtained maximum RE energies at different discharge stages were compared with relativistic test particle simulations that include the effect of toroidal electric field, plasma collisional drag force, synchrotron deceleration force. It was observed that the electrons attain their maximum energies within 50-100 ms after the gas injection. It gradually decreases due to the drop in loop voltage, energy loss due to synchrotron radiation emission and collisions dissipation of energy with the background plasma. HXR measurements at the discharge with multiple deuterium pellet injections allowed observing the effects of plasma cooling and argon ion

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Section: Introductionmentioning

confidence: 97%

Study of runaway electron dynamics at the ASDEX Upgrade tokamak during impurity injection using fast hard x-ray spectrometry

et al. 2021

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“…which reaches up to 15 during current ramp-up, and subsequently decreases to 3 during the density ramp-up phase. The value is larger than the threshold electric field for RE generation in the range of 6-11 in EAST deuterium plasmas, [29] so an initial RE population is created by the electric field during the current ramp-up phase and then dissipated due to increased collisionality.…”

Section: Methodsmentioning

confidence: 95%

“…2(c) and 2(f), the strong hard x-rays (HXR) are detected and indicate that RE has been produced in the current ramp-up phase of the discharges. The ratio of toroidal field to critical field [29] is…”

Section: Methodsmentioning

confidence: 99%

“…A larger E th /E c of deuterium plasma than helium plasma is found in the same current platform, and further proves that the helium plasma can trigger the Dreicer mechanism more efficiently. [29] 0. A certain moment at which the helium plasma and deuterium plasma possess the same electron density is selected to perform the spatial distribution and amplitude of HXR signals as shown in Fig.…”

Section: Re Generation In Helium Plasmamentioning

confidence: 99%

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Runaway electron dynamics in Experimental Advanced Superconducting Tokamak helium plasmas

et al. 2023

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The generation of runaway electrons (REs) is observed during the low-density helium ohmic plasma discharge in the Experimental Advanced Superconducting Tokamak (EAST). The growth rate of hard x-ray (HXR) is inversely proportional to the line-average density. Besides, the RE generation in helium plasma is higher than deuterium plasma at the same density, which is obtained by comparing the growth rate of HXR with the same discharge conditions. The potential reason is the higher electron temperature of helium plasma in the same current and electron density plateau. Furthermore, two Alfvén eigenmodes driven by REs have been observed. The frequency evolution of the mode is not fully satisfied with the Alfvén scaling and when extension of the Alfvén frequency is towards 0, the high frequency branch is ~50 kHz. The different spatial position of the two modes and the evolution of the helium concentration could be used to understand deviation between theoretical and experimental observation.

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“…It is nevertheless of academic interest to understand the effects of REs on the TM stability in a finite-pressure plasma. On the application side, REs are also generated in present-day high-temperature pre-disruption plasmas [33,37]. In the future burning plasma experiments, RE can also be seeded during the pre-thermal quench phase due to tritium decay.…”

Section: Effect Of Res On Tm For Equilibrium With Finite Plasma Pressurementioning

confidence: 99%

Effect of runaway electrons on tearing mode stability: with or without favorable curvature stabilization

Li¹,

Liu²,

Wang³

et al. 2021

Nucl. Fusion

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An MHD-RE hybrid model is developed and implemented into the MARS-F code (Liu et al 2000 Phys. Plasmas 7 3681), where the runaway electrons (REs) are treated as a fluid species. The model is utilized to study the tearing mode (TM) stability in a tokamak plasma, with the numerical results compared to that of the analytic theory. The RE effect on the n = 1 TM is systematically investigated in the absence or presence of the favorable average curvature stabilization (the GGJ-effect). Without the GGJ-effect, for a force-free toroidal plasma equilibrium, REs are found to destabilize the TM and induce a finite real frequency to the mode (in a plasma with vanishing equilibrium flow). The RE contribution is found to significantly enhance the toroidal mode coupling. In the presence of the GGJ-effect, for a plasma with finite equilibrium pressure, the MARS-F hybrid model finds that REs destroy the symmetry in the TM spectrum and introduce extra branch of the TM solution due to the eigenvalue bifurcation. This happens because REs lead to coupling to a stable fluid TM mode and destabilize this mode. Despite complicated mode spectrum introduced by REs, we find that the latter play an overall destabilizing role for the TM also in the presence of the GGJ-effect. The MARS-F computed eigenvalues are well fitted with the analytic dispersion relation derived by Liu et al (2020 Phys. Plasmas 27 092507) for the force-free equilibrium. Less satisfactory is the fitting result with a TM dispersion relation that includes both the GGJ-effect and the RE contribution, suggesting further improvement of the proposed dispersion relation.

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Observation of two threshold fields for runaway-electron generation in tokamaks

Cited by 14 publications

References 34 publications

Study of runaway electron dynamics at the ASDEX Upgrade tokamak during impurity injection using fast hard x-ray spectrometry

Study of runaway electron dynamics at the ASDEX Upgrade tokamak during impurity injection using fast hard x-ray spectrometry

Runaway electron dynamics in Experimental Advanced Superconducting Tokamak helium plasmas

Effect of runaway electrons on tearing mode stability: with or without favorable curvature stabilization

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