自磁箍缩二极管物理特性研究

Self-magnetic pinch diode(SMPD), which is a typical intensive current pinched diode, can radiates high energy (>1MeV) pulsed X ray. The spot of X ray from SMPD is about 2mm that can be used for penetration of implosion material and radiography of hydrodynamic experiments. Pinched characteristic of SMPD is affected by both self magnetic motivated by charged particles movement and beam-plasma interaction between the gap of diode. So far, there is no exact theory or numerical model can explain dynamic principle of SMPD clearly. This item, which integrates with theory, numerical simulation and experiments, aims at research on factors influence on pinched characteristic of electron beam, model of anode plasma emission, principle of beams and plasma interaction, structures of diode and some experiments techniques. First of all, based on the experiments results of SMPD, find a proper way of numerical model to simulate dynamic principle of diode. Then, investigate how to optimize pinched characteristic of electron beam and X ray radiation. Improve current of beams and efficiency of X ray radiation, beams must pinch to the central area as soon as possible by design.

自磁箍缩二极管(SMPD)能够产生焦斑直径约2mm的高能（>1MeV）脉冲X射线，是一种典型的强流箍缩二极管，可用于材料爆轰流体力学和高速运动物体的闪光透视照相等领域。SMPD完全依靠束流自身的磁场和工作过程中产生的等离子体达到强箍缩聚焦,其物理机制非常复杂，目前尚无合适的理论和数值模型能够准确描述其工作过程。 本项目拟采用理论分析、数值模拟和验证实验相结合的方法，研究影响二极管电子束箍缩和聚焦性能的因素，阳极等离子体发射模型，束流与阴阳极等离子体相互作用的机理，二极管几何结构设计及实验技术；建立与实验结果比较符合的并考虑等离子体影响的二极管数值模拟模型；研究改善电子束聚焦性能和X射线输出特性的方法；解决如何使束流尽快箍缩至阳极小尺寸区域、提高束流强度和X射线产生效率等技术问题。

设计并优化了一个采用阳极箔结构加强电子束箍缩聚焦，获得了高剂量、小焦斑X射线输出的自磁箍缩二极管，并配套研制了基于针孔成像原理的X射线焦斑测量系统。开展了~MV条件下的二极管及其焦斑测量系统实验，获得了1.75×2mm的椭圆形X射线焦斑，正前方1m处辐射剂量1.6rad，实验验证了阳极箔加强电子束箍缩聚焦的显著作用；焦斑测量系统在实验中也获得了良好焦斑图像，证明了原理和方法的可行性。实验结果表明研制的自磁箍缩二极管具有结构简单、辐射剂量高、焦斑尺寸较小的优点，具有很强的应用潜力；配套研制的X射线焦斑尺寸测量系统结构简单、成本低廉、工作稳定可靠。X射线的能谱信息是其最重要的参数之一，但是难于直接测量和诊断，本文以数值模拟和实验相结合的方法开展了相关研究。模拟和实验研究发现，二极管电压峰值约为650kV时，计算得到射线平均能量216keV,得到了辐射能谱输出，其衰减规律与叠片法实验吻合良好。