Awe T J, Shelton K P, Sefkow A B, Lamppa D C, Baker J L, Rovang D C, Robertson G K
Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185, USA.
Kansas City National Security Campus, 14520 Botts Rd., Kansas City, Missouri 64147, USA.
Rev Sci Instrum. 2017 Sep;88(9):093515. doi: 10.1063/1.4986041.
A cryogenically cooled hardware platform has been developed and commissioned on the Z Facility at Sandia National Laboratories in support of the Magnetized Liner Inertial Fusion (MagLIF) Program. MagLIF is a magneto-inertial fusion concept that employs a magnetically imploded metallic tube (liner) to compress and inertially confine premagnetized and preheated fusion fuel. The fuel is preheated using a ∼2 kJ laser that must pass through a ∼1.5-3.5-μm-thick polyimide "window" at the target's laser entrance hole (LEH). As the terawatt-class laser interacts with the dense window, laser plasma instabilities (LPIs) can develop, which reduce the preheat energy delivered to the fuel, initiate fuel contamination, and degrade target performance. Cryogenically cooled targets increase the parameter space accessible to MagLIF target designs by allowing nearly 10 times thinner windows to be used for any accessible gas density. Thinner LEH windows reduce the deleterious effects of difficult to model LPIs. The Z Facility's cryogenic infrastructure has been significantly altered to enable compatibility with the premagnetization and fuel preheat stages of MagLIF. The MagLIF cryostat brings the liquid helium coolant directly to the target via an electrically resistive conduit. This design maximizes cooling power while allowing rapid diffusion of the axial magnetic field supplied by external Helmholtz-like coils. A variety of techniques have been developed to mitigate the accumulation of ice from vacuum chamber contaminants on the cooled LEH window, as even a few hundred nanometers of ice would impact laser energy coupling to the fuel region. The MagLIF cryostat has demonstrated compatibility with the premagnetization and preheat stages of MagLIF and the ability to cool targets to liquid deuterium temperatures in approximately 5 min.
为支持磁化内衬惯性聚变（MagLIF）项目，桑迪亚国家实验室在Z装置上开发并启用了一个低温冷却硬件平台。MagLIF是一种磁惯性聚变概念，它采用磁内爆金属管（内衬）来压缩并惯性约束预磁化和预热的聚变燃料。燃料通过一个约2千焦的激光进行预热，该激光必须穿过靶的激光入射孔（LEH）处一个约1.5 - 3.5微米厚的聚酰亚胺“窗口”。当太瓦级激光与致密窗口相互作用时，会产生激光等离子体不稳定性（LPI），这会减少传递到燃料的预热能量，引发燃料污染，并降低靶性能。低温冷却靶通过允许在任何可达到的气体密度下使用薄近10倍的窗口，增加了MagLIF靶设计可触及的参数空间。更薄的LEH窗口可减少难以建模的LPI的有害影响。Z装置的低温基础设施已显著改变，以实现与MagLIF的预磁化和燃料预热阶段兼容。MagLIF低温恒温器通过一个电阻管道将液氦冷却剂直接输送到靶。这种设计在允许由外部类似亥姆霍兹线圈提供的轴向磁场快速扩散的同时，使冷却功率最大化。已开发出多种技术来减轻真空室污染物在冷却的LEH窗口上结冰的积累，因为即使几百纳米厚的冰也会影响激光与燃料区域的能量耦合。MagLIF低温恒温器已证明与MagLIF的预磁化和预热阶段兼容，并且能够在大约5分钟内将靶冷却到液态氘温度。
