Abstract

Shattered pellet injection (SPI) has been chosen as the baseline disruption mitigation system on ITER due to its ability to rapidly inject material deep into the plasma to greatly increase the plasma density and radiate the thermal energy. SPI utilizes a mechanical punch or high-pressure gas to release and accelerate a pellet that has been cryogenically desublimated in the barrel of a pipe gun. Various material injection combinations could possibly be implemented during different phases of a disruption event to radiate plasma energy, reduce electromagnetic loads on machine components, avoid the formation of runaway electrons, or to dissipate runaway electrons that form. Each injection phase could possibly utilize combinations of deuterium, neon, or argon.

In this paper we outline experimental measurements of pellet material shear strength at SPI operating temperatures to understand the force needed to release SPI pellets. Deuterium, neon, argon, and deuterium-neon mixture pellets with diameters of 8.5, 12.5, and 15.7 mm are formed at a range of relevant gas pressures and temperatures and dislodged from the cold zone with a slow-moving piston driven by a motor. The slow-moving piston is kept above the triple point temperature of the material while the pellet is forming, then cooled to below the triple point temperature before contacting the pellet to minimize any thermal conduction to the pellet. The piston incorporates a load cell to measure the force applied when the pellet breaks away from the cold zone in the barrel.

The ability of the gas and punch methods to exceed the shear strength of the studied pellet materials for release has been analyzed.

High-pressure gas delivered by fast-opening valves produce pressure shock to the pellet due to supersonic expansion of the propellant gas. Pressure (and therefore, force) oscillations are present due to transverse density propagation throughout the breech volume. Mechanical punches deliver an impact force through a high-kinetic energy impact. The effect of the mechanical shock on the pellet has been explored and is presented in this paper. Scaling to larger ITER-size SPI pellets will be described.

摘要

破碎颗粒注入 (SPI) 已被选为 ITER 上的基线中断缓解系统，因为它能够将材料快速注入等离子体深处，从而大大增加等离子体密度并辐射热能。SPI 利用机械冲头或高压气体释放和加速在管枪枪管中低温凝华的弹丸。可以在破坏事件的不同阶段实施各种材料注入组合，以辐射等离子体能量、减少机器部件上的电磁负载、避免形成失控电子或耗散形成的失控电子。每个注入阶段都可能使用氘、氖或氩的组合。

在本文中，我们概述了 SPI 操作温度下颗粒材料剪切强度的实验测量，以了解释放 SPI 颗粒所需的力。直径为 8.5、12.5 和 15.7 毫米的氘、氖、氩和氘-氖混合颗粒在相关的气体压力和温度范围内形成，并通过由电机驱动的缓慢移动的活塞从冷区中排出。在颗粒形成时，缓慢移动的活塞保持在材料的三相点温度以上，然后在接触颗粒之前冷却到三相点温度以下，以最大限度地减少对颗粒的任何热传导。活塞包含一个称重传感器，用于测量当颗粒脱离枪管中的冷区时施加的力。

已经分析了气体和冲压方法超过所研究的用于释放的丸粒材料的剪切强度的能力。

由于推进剂气体的超音速膨胀，由快速开启的阀门输送的高压气体对弹丸产生压力冲击。由于贯穿整个后膛体积的横向密度传播，存在压力（因此，力）振荡。机械冲头通过高动能冲击产生冲击力。机械冲击对丸粒的影响已经过探讨，并在本文中进行了介绍。将描述缩放到更大的 ITER 大小的 SPI 颗粒。