Phase-space dynamics of runaway electrons in tokamaks

Guan, Xiaoyin; Qin, Hong; Fisch, Nathaniel J.

doi:doi:10.1063/1.3476268

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Streamer-induced transport in the presence of trapped ion modes in tokamak plasmas

Global gyrokinetic Vlasov simulations for trapped ion modes are performed by solving a Vlasov equation averaged over the cyclotron and bounce motions of trapped ions. The distribution function, for trapped ions, is then calculated in a two-dimensional phase space, parametrized by the longitudinal action (energy) and the magnetic moment in presence of magnetic shear. The physical mechanism of the saturation processes between streamerlike structures and zonal flows in relation to the suppression ...

Plasma shaping effects on the geodesic acoustic mode in the large orbit drift width limit

Plasma shaping effects on the geodesic acoustic mode (GAM) are revisited analytically in the large orbit drift width limit. Comparing with results from the small orbit drift width expansion method [ Z. Gao et al., Phys. Plasmas 15, 074502 (2008) ] the behavior of the real frequency is almost the same but the effect on the damping rate is different due to the change of dominant resonant mechanism, from low order harmonic transit resonance to high order harmonic resonance, or equivalently, to the...

The phase-space dynamics of runaway electrons is studied, including the influence of loop voltage, radiation damping, and collisions. A theoretical model and a numerical algorithm for the runaway dynamics in phase space are developed. Instead of standard integrators, such as the Runge–Kutta method, a variational symplectic integrator is applied to simulate the long-term dynamics of a runaway electron. The variational symplectic integrator is able to globally bound the numerical error for arbitrary number of time-steps, and thus accurately track the runaway trajectory in phase space. Simulation results show that the circulating orbits of runaway electrons drift outward toward the wall, which is consistent with experimental observations. The physics of the outward drift is analyzed. It is found that the outward drift is caused by the imbalance between the increase of mechanical angular momentum and the input of toroidal angular momentum due to the parallel acceleration. An analytical expression of the outward drift velocity is derived. The knowledge of trajectory of runaway electrons in configuration space sheds light on how the electrons hit the first wall, and thus provides clues for possible remedies.

Article Outline

INTRODUCTION
THEORETICAL MODEL AND NUMERICAL ALGORITHM
PHASE-SPACE DYNAMICS OF RUNAWAY ELECTRONS
DISCUSSION AND CONCLUSIONS

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KEYWORDS and PACS

Keywords

plasma drift waves, plasma toroidal confinement, Tokamak devices

PACS

52.20.Dq

Particle orbits
52.35.Bj

Magnetohydrodynamic waves (e.g., Alfven waves)
52.65.Cc

Particle orbit and trajectory

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http://dx.doi.org/10.1063/1.3476268

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1070-664X (print)

1089-7674 (online)

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American Institute of Physics

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