注入电流空间分布对磁绝缘感应电压叠加器性能的影响

Magnetically-insulated induction voltage adders (MIVA) could produce high-power pulses with peak voltage up to tens of megavolt, and peak current up to hundreds of kiloampere, which play a key role in effect simulations and x-ray radiography. The spatial distributions of current feeding each cavity affect the operating characteristic and output parameters of MIVA greatly. However, these effects are unclear presently. In addition, there is also a lack of physical models, to describe the effects of asymmetric feed currents on magnetic insulation and power flow in the secondary region of MIVA. . In this work, with consideration of the effects of asymmetric feed, a two dimensional Creedon model will be developed to describe the process of magnetic insulation with an asymmetric electron sheath. Combined with three-dimension PIC simulations, this model will be used to investigate the mechanism and relationship between the spatial distributions of currents and the magnetic insulation behavior. Transient electromagnetism and circuit models will be established, to obtain the influence extent of the spatial distributions of feed currents on operating characteristic of cavities and output parameters. In the end, some current injection experiments will be conducted to investigate these influences of spatial distributions of feed currents, and to validate the aforementioned models and simulation results. This work will provide helpful guidance for the future physical design of MIVA accelerators.

磁绝缘感应电压叠加器(Magnetically-Insulated Induction Voltage Adder,MIVA)能够产生数十兆伏、数百千安的高功率电脉冲，在效应模拟和闪光X射线照相等领域具有重要应用。注入电流空间分布对感应腔工作特性和MIVA输出参数具有重要影响，目前其影响程度尚不十分清楚。电流非均匀注入对MIVA次级磁绝缘和功率传输的作用机制也缺乏精确模型来描述。.本项目拟考虑感应腔注入电流空间分布的影响，建立二维Creedon层流模型，结合三维粒子模拟，认识注入电流空间分布对MIVA次级磁绝缘行为的作用机制。建立MIVA瞬态电磁和电路模型，获得注入电流分布对感应腔工作特性和输出参数的影响规律。开展感应腔注入电流实验，实验研究注入电流分布对MIVA次级磁绝缘的影响，验证所建立模型和仿真结果。项目研究将为MIVA型强流加速器的物理设计提供理论依据和参考。

针对磁绝缘感应电压叠加器（MIVA）感应腔注入电流非均匀分布引起的非轴对称磁绝缘问题，建立了圆柱坐标系下稳态磁绝缘二维层流物理模型，提出了一种确定非轴对称磁绝缘电子鞘层的方法。在给定阴极电流（或阴极表面磁感应强度）空间分布时，给出了物理模型的数值求解算法；获得了典型磁绝缘参数（线电压4MV、最小磁绝缘阳极电流132kA、阳极半径0.2m、阴极电流不均匀系数25%）下MIVA次级非轴对称磁绝缘特性（电磁场、电子鞘层边界、空间电子密度等）的二维分布，结果表明：当阴极电流空间上满足余弦分布时，磁绝缘电子鞘层边界呈高斯分布；阳极电流空间分布均匀性优于阴极，且与阴极电流分布存在相位差。上述数值分析结果与美国RITS-3装置上的实验结果相吻合。研究了电流非均匀分布对MIVA磁绝缘特性的影响规律：注入电流非均匀分布对磁绝缘电子鞘层的影响较大，会引起电子鞘层偏心，极端情况下，电流非均匀分布可能引起磁绝缘阴-阳间隙局部短路；电流非均匀分布对磁绝缘流阻抗的影响较小，即使在阴-阳间隙局部短路时，流阻抗降低约13%；电流非均匀分布的影响程度与磁绝缘运行参数（线电压、最小阳极电流等）密切相关。在两级感应腔串联MIVA平台上开展了验证性实验（磁绝缘线电压约500kV，最小阳极电流约130kA），部分校验了物理模型及数值求解方法的准确性。