Early time radiation symmetry at the capsule for indirect drive ignition on the National Ignition Facility (NIF) G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, 228 (2004) will be inferred from the instantaneous soft x-ray re-emission pattern of a high-Z sphere replacing the ignition capsule. This technique was tested on the OMEGA laser facility J. M. Soures, R. L. McCrory, T. Boehly, Laser Part. Beams 11, 317 (1991) in near full ignition scale vacuum hohlraums using an equivalent experimental setup to the one planned for NIF. Two laser cones entering each laser entrance hole heat the hohlraums to radiation temperatures of 100 eV, mimicking the NIF ignition pulse foot drive. The experiments have demonstrated accuracies of ±1.5% (±2%) in inferred P_2P_0 (P_4P_0) Legendre mode incident flux asymmetry and consistency between 900 eV and 1200 eV re-emission patterns. We have also demonstrated the expected tuning capability of P _2P_0, from positive (pole hot) to negative (waist hot), decreasing linearly with the innerouter beams power fraction. P 4P0 on the other hand shows very little variation with power fraction. We developed a simple analytical viewfactor model that is in good agreement with both measured P_2P_0 and P _4P_0 and their dependence on inner beam power fraction.
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机译：国家点火装置（NIF）上用于间接驱动点火的胶囊处的早期辐射对称性G. H. Miller，E. I. Moses和C. R. Wuest，Nucl。从取代点火胶囊的高Z球体的瞬时软X射线再发射模式可以推断出Fusion 44、228（2004年）。该技术已在OMEGA激光设备J.M.Soures，R.L.McCrory，T.Boehly的Laser Part上进行了测试。在接近完全点火规模的真空水平仪中使用第11、317（1991）条光束，采用与NIF计划的等效的实验装置。进入每个激光入射孔的两个激光锥将水平仪加热到100 eV的辐射温度，模仿了NIF点火脉冲脚驱动器。实验表明，推断的P_2P_0（P_4P_0）勒让德模式入射通量不对称性和900 eV与1200 eV重发射模式之间的一致性，精度为±1.5％（±2％）。我们还证明了P _2P_0的预期调谐能力，从正（极热）到负（腰热），随内外光束功率分数线性降低。另一方面，P 4P0随功率分数的变化很小。我们开发了一个简单的分析视力因数模型，该模型与测得的P_2P_0和P _4P_0以及它们对内光束功率分数的依赖关系很好。
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