Abstract

Shattered pellet injector systems have been installed on DIII-D, JET, and KSTAR and used to experimentally determine the effectiveness of the shattered pellet injection (SPI) process in mitigating the deleterious effects of a tokamak plasma disruption. Pellets are fired, and before entering the plasma, strike a bent tube known as a shatter tube causing the pellet to shatter. The process of pellet fragmentation is a chaotic process that can be described in terms of fragment size distribution through a statistical model that incorporates the effects of the pellet material and impact characteristics. In addition to the fragment size distribution, the shatter plume has other characteristics of interest, such as a fragment velocity distribution and temporal mass evolution. The fragment velocity distribution is important because it is needed to accurately model the spread and location of the ablation and the deposition of impurities in the plasma over time. The temporal mass evolution is necessary to determine the time-resolved delivery of mass to the plasma.

Due to installation constraints, the shatter tube currently installed on JET has a unique geometry with a modest S-bend followed by a 20-deg bend at the end of the tube. The DIII-D and KSTAR shatter tube design is a simple tube bent through an angle of 20 deg followed by a straight section. The resulting shatter sprays from the JET shatter tube and a 20-deg miter bend shatter tube were experimentally characterized for various pellet materials and speeds. Laboratory testing of these shatter tubes allows for the use of fast cameras to capture the fragment spray traveling through a large vacuum chamber. These high-speed videos of the shatter plumes allow the fragment size distribution, temporal mass evolution, and velocity distribution of the fragments within the plume to be determined. This paper presents a comparison of the unique geometry of the JET shatter tube to the miter bend geometries used for shattering and some insight into the variables that may be adjusted to produce the optimal shatter spray. The impact of entrained propellant gas on the resulting shatter spray was examined during testing.

摘要

破碎的颗粒注入器系统已安装在DIII-D，JET和KSTAR上，用于通过实验确定破碎的颗粒注入（SPI）工艺在减轻托卡马克等离子体破坏的有害影响方面的有效性。丸粒被发射，并且在进入等离子体之前，撞击被称为粉碎管的弯曲管，导致丸粒粉碎。粒料破碎的过程是一个混乱的过程，可以通过统计模型描述碎屑的大小分布，该统计模型结合了粒料的影响和冲击特性。除碎片大小分布外，碎片羽还具有其他令人感兴趣的特性，例如碎片速度分布和时间质量演化。碎片速度分布很重要，因为需要精确模拟消融的扩散和位置以及等离子体中杂质随时间的沉积。时间质量演化对于确定质量到血浆的时间分辨传递是必需的。

由于安装限制，当前安装在JET上的破碎管具有独特的几何形状，具有适度的S形弯曲，然后在管的末端弯曲20度。DIII-D和KSTAR破碎管设计是一个简单的管，弯曲成20度角，然后是笔直的部分。从JET粉碎管和20度斜切弯曲粉碎管得到的粉碎喷雾通过实验表征了各种颗粒材料和速度。这些粉碎管的实验室测试允许使用快速相机捕获穿过大真空室的碎片喷雾。碎片羽流的这些高速视频允许确定碎片在羽流中的大小分布，时间质量演化和速度分布。本文介绍了JET破碎管的独特几何形状与用于破碎的斜接弯曲几何形状的比较，并对可以调整以产生最佳破碎喷雾的变量有所了解。在测试过程中检查了夹带的推进剂气体对所产生的破碎喷雾的影响。