A dense plasma focus (DPF) nuclear fusion device is an attractive pulsed neutron source in many applications, due to its relatively large neutron yield, produced in a short time duration. To design a DPF that generates neutrons within a specified time profile, or that generates a neutron energy spectrum with specific properties, it is necessary to characterize and model the results of the fusion process releasing the neutrons. The time–energy spectrum of fusion neutrons is an ideal quantity used in validating multiphysics codes that simulate the pinch and fusion processes, because it is a quantity that requires physics of each of the stages leading up to and ending in the fusion reaction to be simulated correctly. In particular, since DPF fusion neutrons are not monoenergetic—and there can often be several fusion pinches creating neutrons—a computer simulation matching high quality neutron spectrum measurements provides confidence in the fidelity of the simulation. In order to make such a comparison, it is first necessary to have quality measurements from which to infer the spectrum. In this work, we project neutron spectroscopy as the classical tomographic inverse problem from neutron time-of-flight data at multiple distances, but enhanced by using an additional measurement of the time profile of the fusion pinch near its source and by using detector pairs set up in a geometry that allows for scatter background subtraction. The detector pairs enhance the quality of the time-of-flight measurements, and the additional constraint posed by the measured time profile allows for reconstructions discretized as finely as the time measurements and in energy as finely as 100 keV, without the problem being underdetermined. We present results from a deuterium-fueled DPF at the U.S. Department of Energy’s Nevada National Security Site and show that we can infer the time–energy spectrum from our measurements for both single and multi-pinch fusion reactions with equal fidelity.

中文翻译：

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稠密等离子体焦点的中子时能谱断层扫描重建


密集等离子体聚焦（DPF）核聚变装置在许多应用中是一种有吸引力的脉冲中子源，因为它在短时间内产生相对较大的中子产量。为了设计在指定时间范围内产生中子或产生具有特定属性的中子能谱的 DPF，有必要对释放中子的聚变过程的结果进行表征和建模。聚变中子的时间-能量谱是用于验证模拟箍缩和聚变过程的多物理场代码的理想量，因为它需要模拟聚变反应之前和结束的每个阶段的物理量正确。特别是，由于 DPF 聚变中子不是单能的，并且通常可能有多个聚变箍缩产生中子，因此与高质量中子能谱测量相匹配的计算机模拟可以为模拟的保真度提供信心。为了进行这样的比较，首先需要进行质量测量来推断频谱。在这项工作中，我们将中子能谱投影为来自多个距离的中子飞行时间数据的经典断层摄影反演问题，但通过使用其源附近聚变箍缩的时间剖面的附加测量以及使用探测器对组来增强中子谱处于允许散射背景扣除的几何形状中。探测器对提高了飞行时间测量的质量，并且由测量的时间分布所带来的附加约束允许重建与时间测量一样精细的离散化以及在能量上与100 keV一样精细的离散化，而不会出现未确定的问题。我们展示了美国的氘燃料 DPF 的结果 能源部内华达国家安全站点并表明，我们可以从单捏聚变反应和多捏聚变反应的测量中以相同的保真度推断出时间-能量谱。