Efficient Optimization of Plasma Radiation Detector Configurations using Imperfect Inference Models

The configurations of instruments fielded on an experiment affect the amount of information captured and the quality of subsequent inference. We investigate the problem of optimizing plasma x-ray radiation detectors in a magneto-inertial fusion experiment at Sandia National Laboratories. It is impossible to directly measure properties such as the temperature of the thermonuclear fusion plasma produced in these experiments because of the extreme environment and destructive nature of the experiment. Among other diagnostics, several detectors are placed with significant standoff from the fusion target to capture the x-rays emitted by the fusion plasma, which can be used to infer some of its properties. To optimize the configuration of these detectors, a high-fidelity model (HFM) is used for simulating outputs and a low-fidelity model (LFM) is used for inference. We develop methods based on A- and L-optimality criteria that are efficient to compute while explicitly accounting for the discrepancy between the HFM and the LFM. The method allows us to find detector configurations that perform similarly to or better than the configuration obtained using an existing sampling-based optimization method while decreasing computational time by a factor of 50. Supplementary materials for this article are available online, including a standardized description of the materials available for reproducing the work.

实验中部署的仪器配置，会影响所采集的信息量与后续推断的质量。我们针对桑迪亚国家实验室的磁惯性聚变实验，开展等离子体X射线辐射探测器优化问题的研究。由于此类实验所处环境极端且具有破坏性，无法直接测量实验中产生的热核聚变等离子体的温度等属性。在各类诊断设备中，我们在与聚变靶体留有显著间距的位置部署了多台探测器，以捕获聚变等离子体辐射出的X射线，进而推断等离子体的部分属性。为优化这些探测器的配置，我们采用高保真模型（high-fidelity model, HFM）进行输出仿真，并用低保真模型（low-fidelity model, LFM）开展推断工作。我们基于A最优准则与L最优准则开发了计算高效的方法，该方法可显式考量高保真模型与低保真模型之间的偏差。该方法可帮助我们找到性能不亚于甚至优于现有基于采样的优化方法所得探测器配置的方案，同时将计算耗时缩减至原有水平的1/50。本文的补充材料可在线获取，其中包含可用于复现本研究工作的标准化材料说明。