Shattered pellet penetration in low and high energy plasmas on DIII-D

Shattered pellet injection (SPI) has been adopted as the baseline disruption mitigation system for ITER, as the radiative payload penetration into DIII-D plasmas from SPI is superior to those using the massive gas injection (MGI) method. Because of the substantial differences in the energy content of ITER plasma and those in present experiments, reliable 3D MHD modeling, benchmarked against present experiments is needed to project to ITER plasmas. In support of these needs, the depth of SPI fragment penetration in DIII-D plasmas was investigated by injecting SPI into two discharges with vastly different energy content and pedestal height. 400 Torr-L pure Ne fragmented pellets at a velocity of about 200 m s−1 were injected into a 0.2 MJ L-mode discharge and a 2 MJ super H-mode discharge. Results show deep penetration of SPI fragments into low-energy plasmas in DIII-D. SPI fragment penetration is reduced as the plasma energy content increases, with some discharges exhibiting penetration that is confined to the outer regions of the plasma. The injected SPI fragments are also spread out over a distance of about 20 cm, which results in some fragments arriving near the end of or after the thermal quench is over.碎裂弹丸注入（Shattered Pellet Injection, SPI）已被确立为国际热核聚变实验堆（ITER）的基准破裂缓解系统，原因在于SPI将辐射载荷穿透入DIII-D等离子体的性能优于大规模气体注入（Massive Gas Injection, MGI）方法。鉴于ITER等离子体与当前实验装置的等离子体在能量含量上存在显著差异，因此需要以当前实验为基准进行校准的可靠三维磁流体动力学（3D MHD）建模，以实现对ITER等离子体工况的外推。为满足上述需求，本研究通过向两个能量含量与边缘输运垒高度差异显著的等离子体放电实验中注入SPI，探究了DIII-D等离子体中SPI弹丸碎片的穿透深度。实验中以约200 m·s⁻¹的速度，将400托-升（Torr-L）的纯氖（Ne）碎裂弹丸分别注入至0.2 MJ的L模等离子体放电与2 MJ的超H模等离子体放电中。实验结果显示，SPI弹丸碎片可深入穿透DIII-D装置中的低能量等离子体。随着等离子体能量含量提升，SPI弹丸碎片的穿透深度会随之降低，部分放电实验中的碎片穿透被限制在等离子体的外围区域。注入的SPI弹丸碎片还会在约20 cm的范围内发生扩散，这导致部分碎片在热猝灭过程末期或热猝灭结束后才抵达靶区。