Reconstructing 3-D Asymmetries in Laser-Direct-Drive Implosions on OMEGA

Three-dimensional reconstruction algorithms have been developed which determine the hot-spot velocity, hot-spot apparent ion temperature distribution, and fuel areal-density distribution present in laser-direct- drive inertial confinement fusion implosions on the OMEGA laser. These reconstructions rely on multiple independent measurements of the neutron energy spectrum emitted from the fusing plasma. Measurements of the neutron energy spectrum on OMEGA are made using a suite of quasi-orthogonal neutron time-of-flight detectors and a magnetic recoil spectrometer. These spectrometers are positioned strategically around the OMEGA target chamber to provide unique 3-D measurements of the conditions of the fusing hot spot and compressed fuel near peak compression. The uncertainties involved in these 3-D reconstructions are discussed and are used to identify a new nTOF diagnostic line of sight which when built will reduce the uncertainty in the hot-spot apparent ion temperature distribution from 700 to <400 eV.

针对OMEGA激光器上开展的激光直接驱动惯性约束聚变内爆实验，本研究开发了可获取聚变热点速度、热点表观离子温度分布以及燃料面密度分布的三维重建算法。此类重建依赖于对聚变等离子体发射的中子能谱的多组独立测量。OMEGA装置的中子能谱测量采用一套准正交中子飞行时间（neutron Time-of-Flight, nTOF）探测器组与磁反冲动谱仪完成。这些探测装置被合理布置在OMEGA靶室周围，可获取聚变热点与压缩燃料在峰值压缩时刻的独有三维状态测量数据。本文讨论了此类三维重建过程中涉及的各项不确定度，并基于此确定了一条新型nTOF诊断视线路径；该路径建成后，可将热点表观离子温度分布的测量不确定度从700 eV降至400 eV以下。