The radial density profile of pre-thermal quench (pre-TQ) early-time non-thermal (hot) electrons is estimated by combining electron cyclotron emission and soft x-ray data during the rapid shutdown of low-density ($n_e\lesssim {10}^{19}\hspace{0.17em}{\mathrm{m}}^{-3})$ DIII-D target plasmas with cryogenic argon pellet injection. This technique is mostly limited in these experiments to the pre-TQ phase and quickly loses validity during the TQ. Two different cases are studied: a high (10 keV) temperature target and a low (4 keV) temperature target. The results indicate that early-time, low-energy (∼10 keV) hot electrons form ahead of the argon pellet as it enters the plasma, affecting the pellet ablation rate; it is hypothesized that this may be caused by rapid cross field transport of argon ions ahead of the pellet or by rapid cross field transport of hot electrons. Fokker–Planck modeling of the two shots suggests that the hot electron current is quite significant during the pre-TQ phase (up to 50% of the total current). Comparison between modeled pre-TQ hot electron current and post-TQ hot electron current inferred from avalanche theory suggests that hot electron current increases during the high-temperature target TQ but decreases during the low-temperature target TQ. The uncertainties in this estimate are large; however, if true, this suggests that TQ radial loss of hot electron current could be larger than previously estimated in DIII-D.

中文翻译：

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在 DIII-D 中低密度靶等离子体的 Ar 颗粒关闭期间预热淬火非热电子密度分布的估计

通过结合电子回旋发射和低密度快速关闭期间的软 X 射线数据估计预热猝灭 (pre-TQ) 早期非热（热）电子的径向密度分布（$n_{\mathrm{电子}}\lesssim {10}^{19}\hspace{0.17em}{\mathrm{米}}^{-3})$DIII-D 目标等离子体与低温氩颗粒注射。这种技术在这些实验中主要限于前 TQ 阶段，并在 TQ 期间迅速失去有效性。研究了两种不同的情况：高 (10 keV) 温度目标和低 (4 keV) 温度目标。结果表明，当氩颗粒进入等离子体时，早期的低能量 (~10 keV) 热电子会在其之前形成，从而影响颗粒烧蚀速率；据推测，这可能是由于小球之前氩离子的快速交叉场传输或热电子的快速交叉场传输造成的。两次发射的福克-普朗克模型表明，热电子电流在前 TQ 阶段非常重要（高达总电流的 50%）。从雪崩理论推断出的模拟前 TQ 热电子电流和后 TQ 热电子电流之间的比较表明，热电子电流在高温目标 TQ 期间增加，但在低温目标 TQ 期间减少。这个估计的不确定性很大；然而，如果为真，这表明热电子流的 TQ 径向损失可能比先前在 DIII-D 中估计的要大。