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arXiv 2401.11291physics.plasm-ph
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托卡马克破裂期间碰撞性对逃逸电子雪崩的影响

The Impact of Collisionality on the Runaway Electron Avalanche during a Tokamak Disruption

Jonathan Arnaud, Christopher McDevitt

AI总结:

本文研究托卡马克破裂中环形几何对逃逸电子雪崩效率的影响,发现临界碰撞性参数$ν_{*, crit}$可区分氘等离子体中的效率降低与高Z杂质等离子体中的无减弱效应。

摘要:

托卡马克破裂期间逃逸电子(REs)的指数增长(雪崩化)仍然是RE建模中的一大不确定性。本工作研究了在广泛破裂情景范围内,托卡马克几何对雪崩机制效率的影响。研究发现,描述达到逃逸所需临界能量处碰撞性的参数$ν_{*, crit}$,刻画了环形几何如何影响RE形成。特别是,利用一种简化但自洽的等离子体功率平衡描述,结果表明对于高密度、以氘为主的等离子体,$ν_{* crit}$稳定小于一,导致与平板几何预测相比,RE雪崩效率显著降低。相比之下,对于含有大量氖或氩的等离子体,$ν_{*, crit} \gtrsim 1$,未观察到由环形几何引起的雪崩减弱。低Z与高Z材料影响之间的这种鲜明对比,主要源于高Z杂质相对较强的辐射冷却,使等离子体能够被辐射钉扎在低温,从而即使在高Z材料数量适中时也能产生大电场。

英文摘要:

The exponential growth (avalanching) of runaway electrons (REs) during a tokamak disruption continues to be a large uncertainty in RE modeling. The present work investigates the impact of tokamak geometry on the efficiency of the avalanche mechanism across a broad range of disruption scenarios. It is found that the parameter $ν_{*, crit}$ describing the collisionality at the critical energy to run away delineates how toroidal geometry impacts RE formation. In particular, utilizing a reduced but self-consistent description of plasma power balance, it is shown that for a high-density deuterium-dominated plasma, $ν_{*, crit}$ is robustly less than one, resulting in a substantial decrease in the efficiency of the RE avalanche compared to predictions from slab geometry. In contrast, for plasmas containing a substantial quantity of neon or argon, $ν_{*, crit} \gtrsim 1$, no reduction of the avalanche is observed due to toroidal geometry. This sharp contrast in the impact of low-versus high-Z material results primarily from the relatively strong radiative cooling from high-Z impurities, enabling the plasma to be radiatively pinned at low temperatures and thus large electric fields, even for modest quantities of high-Z material.

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