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arXiv 2303.01153physics.plasm-ph
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电流淬灭期间逃逸电子电流主导平衡的漂移面求解器

Drift surface solver for runaway electron current dominant equilibria during the Current Quench

Lu Yuan, Di Hu

AI总结:

针对托卡马克破裂电流淬灭阶段的逃逸电子电流问题,推导类Grad-Shafranov方程求解其轴对称漂移面,数值模拟揭示动量变化等因素对电流中心位移的影响,为平衡与稳定性研究奠基。

摘要:

托卡马克破裂的电流淬灭阶段产生的逃逸电子电流可能对未来高性能装置造成严重损害。为控制并缓解此类逃逸电子电流,准确描述以逃逸电子电流为主的平衡态至关重要,后续可基于此开展进一步的稳定性分析。本文推导了一个类Grad-Shafranov方程,用于求解所有逃逸电子具有相同平行动量这一简单情形下逃逸电子的轴对称漂移面。随后采用具有ITER类和MAST类几何参数的简单矩形壁,对该新平衡方程进行数值求解。我们轻松得到了漂移面与通量面之间的偏差,并且发现即使在具有开放磁力线的区域,逃逸电子也能被良好约束。研究发现,逃逸电子平行动量的变化会导致电流中心发生水平位移,而总电流或外场不会发生任何变化。逃逸电流密度剖面会影响这种位移的敏感性,剖面越平坦,相同动量变化引起的位移就越大。当外部极向场存在上下不对称性时,这种位移会伴随逃逸电子电流的垂直位移。研究发现,这种效应在更小、更紧凑的装置以及极向场更弱的情况下更为显著。上述结果阐明了由逃逸电子动量空间变化引起的电流中心位移的动力学特性,并为未来更完善的、更真实考虑逃逸电子动量分布的逃逸电流平衡理论铺平了道路。这一新的平衡理论也为未来逃逸电子电流的稳定性分析奠定了基础。

英文摘要:

Runaway electron current generated during the Current Quench phase of tokamak disruptions could result in severe damage to future high performance devices. To control and mitigate such runaway electron current, it is important to accurately describe the runaway electron current dominated equilibrium, based on which further stability analysis could be carried out. In this paper, we derive a Grad-Shafranov-like equation solving for the axisymmetric drift surfaces of the runaway electrons for the simple case that all runaway electron share the same parallel momentum. This new equilibrium equation is then numerically solved with simple rectangular wall with ITER-like and MAST-like geometry parameters. The deviation between the drift surfaces and the flux surfaces is readily obtained, and runaway electrons is found to be well confined even in regions with open field lines. The change of the runaway electron parallel momentum is found to result in a horizontal current center displacement without any changes in the total current or the external field. The runaway current density profile is found to affect the susceptibility of such displacement, with flatter profiles result in more displacement by the same momentum change. With up-down asymmetry in the external poloidal field, such displacement is accompanied by a vertical displacement of runaway electron current. It is found that this effect is more pronounced in smaller, compact device and weaker poloidal field cases. The above results demonstrate the dynamics of current center displacement caused by the momentum space change in the runaway electrons, and pave way for future, more sophisticated runaway current equilibrium theory with more realistic consideration on the runaway electron momentum distribution. This new equilibrium theory also provides foundation for future stability analysis of the runaway electron current.

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