Phased plan for the implementation of the time-resolving magnetic recoil spectrometer on the National Ignition Facility (NIF)

The time-resolving magnetic recoil spectrometer (MRSt) is a transformative diagnostic that will be used to measure the time-resolved neutron spectrum from an inertial confinement fusion implosion at the National Ignition Facility (NIF). It uses a CD foil on the outside of the hohlraum to convert fusion neutrons to recoil deuterons. An ion-optical system positioned outside the NIF target chamber energy-disperses and focuses forward-scattered deuterons. A pulse-dilation drift tube (PDDT) subsequently dilates, un-skews, and detects the signal. While the foil and ion-optical system have been designed, the PDDT requires more development before it can be implemented. Therefore, a phased plan is presented that first uses the foil and ion-optical systems with detectors that can be implemented immediately—namely CR-39 and hDISC streak cameras. These detectors will allow the MRSt to be commissioned in an intermediate stage and begin collecting data on a reduced timescale, while the PDDT is developed in parallel. A CR-39 detector will be used in phase 1 for the measurement of the time-integrated neutron spectra with excellent energy-resolution, necessary for the energy calibration of the system. Streak cameras will be used in phase 2 for measurement of the time-resolved spectrum with limited spectral coverage, which is sufficient to diagnose the time-resolved ion temperature. Simulations are presented that predict the performance of the streak camera detector, indicating that it will achieve excellent burn history measurements at current yields, and good time-resolved ion-temperature measurements at yields above 3 × 10^17. The PDDT will be used for optimal efficiency and resolution in phase 3.

时间分辨磁反冲谱仪（time-resolving magnetic recoil spectrometer, MRSt）是一款具有变革性的诊断装置，将用于在国家点火装置（National Ignition Facility, NIF）上测量惯性约束聚变内爆产生的时间分辨中子能谱。该装置通过黑腔外侧的碳氘（CD）箔将聚变中子转换为反冲氘核；位于NIF靶室外侧的离子光学系统对前向散射的氘核进行能量色散与聚焦；随后由脉冲漂移扩张管（pulse-dilation drift tube, PDDT）完成信号的扩张、去畸变与探测。尽管碳氘箔与离子光学系统已完成设计，但脉冲漂移扩张管仍需进一步开发才能投入使用。为此，本文提出分阶段实施方案：第一阶段先采用可立即部署的探测器（即CR-39探测器与hDISC条纹相机）搭配碳氘箔与离子光学系统，在脉冲漂移扩张管并行开发的同时，完成MRSt的中期调试并在缩短的时间尺度内启动数据采集。第一阶段将使用CR-39探测器开展时间积分中子能谱测量，其优异的能量分辨率可用于系统的能量标定；第二阶段将采用条纹相机开展光谱覆盖范围有限的时间分辨能谱测量，该方案足以用于诊断时间分辨离子温度。本文还给出了预测条纹相机探测器性能的数值模拟结果，表明其在当前聚变产额下可实现出色的燃烧历史测量，且在产额高于3×10^17时可获得良好的时间分辨离子温度测量结果；第三阶段将部署脉冲漂移扩张管，以实现最优的探测效率与分辨率。