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arXiv 2002.05241physics.plasm-ph
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反应堆相关温度下的逃逸电子种子形成

Runaway Electron Seed Formation at Reactor-Relevant Temperature

C. Paz-Soldan, P. Aleynikov, E. M. Hollmann, A. Lvovskiy, I. Bykov, X. Du, N. W. Eidietis, D. Shiraki

摘要:

使用内部传输势垒的情况下,从1到12千电子伏的分裂前核心电子温度(Te)的系统变化揭示了种子逃逸电子(RE)的生产急剧增加,最终接近完全转换的分裂前电流到亚MeV RE电流。观察到注入的Ar颗粒烧蚀更强烈,更迅速地作为Te上升。在高Te,所观察到的烧蚀超过预测从公布的热烧蚀模型。同时,观察到热猝灭(TQ)随着Te的增加而显著缩短-这是令人惊讶的结果。虽然TQ较短的原因尚不清楚,但候选机制包括:不够准确的热消融模型,由种子RE群体驱动的增强消融,或沿随机场的显著平行热传输。动力学建模,自洽地对待通过辐射等离子体冷却,诱导的电场,和种子RE的形成进行。包括热尾RE播种对Te的固有依赖性与缩短的TQ的组合效应,建模恢复了随着Te上升而接近完全转换的预中断电流到RE电流的进展。在早期电流猝灭(CQ)期间的HXR光谱的测量揭示了随预破裂Te的能量降低的趋势。在最高Te($\approx$ 12 keV)时,发现热电流向逃逸电流的$\approx$ 100%转换,这一特殊的稀土束的能量被推断为亚MeV,因为它发射的硬X射线(HXR)几乎为零。这些测量结果表明,新的TQ动态Te是不同的,并说明了治疗的RE种子形成问题的局限性,而不考虑相互关联的依赖性的弹丸烧蚀,辐射能量损失,和由此产生的TQ持续时间的变化。

英文摘要:

Systematic variation of the pre-disruption core electron temperature (Te) from 1 to 12 keV using an internal transport barrier scenario reveals a dramatic increase in the production of seed runaway electrons (REs), ultimately accessing near-complete conversion of the pre-disruption current into sub-MeV RE current. Injected Ar pellets are observed to ablate more intensely and promptly as Te rises. At high Te, the observed ablation exceeds predictions from published thermal ablation models. Simultaneously, the thermal quench (TQ) is observed to significantly shorten with increasing Te -- a surprising result. While the reason for the shorter TQ is not yet understood, candidate mechanisms include: insufficiently accurate thermal ablation models, enhanced ablation driven by the seed RE population, or significant parallel heat transport along stochastic fields. Kinetic modeling that self-consistently treats the plasma cooling via radiation, the induced electric field, and the formation of the seed RE is performed. Including the combined effect of the inherent dependence of hot-tail RE seeding on Te together with the shortened TQ, modeling recovers the progression towards near-complete conversion of the pre-disruption current to RE current as Te rises. Measurement of the HXR spectrum during the early current quench (CQ) reveals a trend of decreasing energy with pre-disruption Te. At the very highest Te ($\approx$ 12 keV), $\approx$ 100% conversion of the thermal current to runaway current is found. The energy of this peculiar RE beam is inferred to be sub-MeV as it emits vanishingly few MeV hard X-rays (HXRs). These measurements demonstrate novel TQ dynamics as Te is varied and illustrate the limitations of treating the RE seed formation problem without considering the inter-related dependencies of the pellet ablation, radiative energy loss, and resultant variations of the TQ duration.

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