Particle in cell and hybrid simulations of the Z double-post-hole convolute cathode plasma evolution and dynamics
Particle in cell and hybrid simulations of the Z double-post-hole convolute cathode plasma evolution and dynamics
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Z 双柱孔回旋阴极等离子体演化和动力学的电池中粒子和混合模拟
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
S. Vickers
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文献类型：
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作者：
S. Vickers
桑迪亚国家实验室（SNL）的Z加速器是一种高电流脉冲功率机器，用于驱动一系列高能量密度物理（HEDP）实验[1]。为了实现> 20 MA的峰值电流，在100 ns的上升时间内，电流被分配到四个等级的传输线上，然后在双柱孔回旋（DPHC）中并联添加，并通过单个内部磁绝缘传输线（MITL）输送到负载。阴极电极上的电场，> 107 Vm −1，驱动中性污染物的解吸和电离，形成等离子体，电子从等离子体发射到阳极-阴极（a-k）间隙中。DPHC中的电流添加路径形成磁性“零”区域，穿过该区域电子损失到阳极，分流来自内部MITL和负载的电流。在实验中，在回旋内测量到>10%的电流损耗;这降低了输送到负载的功率，对负载性能产生负面影响，并且使用于驱动详细磁流体动力学（MHD）模拟的坡印亭通量的预测复杂化[2，3]。在这篇论文中，我们发展了三维的粒子-细胞（PIC）和混合流体-PIC计算机模型来模拟DPHC和内部MITL中的等离子体演化。在模拟中，氢等离子体以0.0075mlns−1（1 ml = 1015 cm −2）的速率从阴极注入，初始温度为3eV，在峰值电流下的预期实验电流损失与模拟相匹配。模拟的电流损失是由等离子体穿透阳极柱的下游侧，减少有效a-k间隙间距和增强阳极的电子损失驱动的。在早期（<10 MA）的电流损失，在模拟中匹配，其中空间电荷限制（SCL）电子发射允许直接从阴极;为了匹配整个电流脉冲的损失，延迟模型是有动机的。在这里，等离子体注入延迟在SCL发射开始之后，基于实际的等离子体膨胀速度为1.3cm μs−1。PIC模型是精确模拟低密度等离子体和带电粒子鞘的动力学行为所必需的，计算密集，使得在3D模拟中实现的空间分辨率相对较差。为了减少计算开销，允许更精细的空间分辨率被访问的目的，我们调查hyBritish Crown Copyright 2012/MOD iii brid技术模拟回旋中的阴极等离子体的适用性。我们的PIC模型都是在电阻MHD代码，Gorgon，其中部分的等离子体建模在单流体近似，并扩展到包括一个惯性两流体描述的等离子体。混合动力模型应用于DPHC模拟，其结果被用来激励一个三分量模型;在这里，回旋等离子体的dendrone部分使用单流体MHD近似建模，过渡到一个完全动力学PIC描述的低密度等离子体和带电粒子鞘，连接由两种流体的描述。British Crown Copyright 2012/MOD iv c ©Crown Copyright 2012“本文件由大不列颠及北方爱尔兰联合王国国防大臣财产的材料组成或改编而成。本文件为机密文件，未经D/IPR，MOD，修道院伍德，布里斯托，BS 34 8 JH，UK事先书面同意，不得进一步复制、使用或披露全部或部分内容。”
The Z-accelerator at Sandia National Laboratories (SNL), is a high-current pulsed power machine used to drive a range of high energy density physics (HEDP) experiments [1]. To achieve peak currents of >20MA, in a rise time of ∼100ns, the current is split over four levels of transmission line, before being added in parallel in a double-post-hole convolute (DPHC) and delivered to the load through a single inner magnetically insulated transmission line (MITL). The electric field on the cathode electrode, >107Vm−1, drives the desorption and ionisation of neutral contaminants to form a plasma from which electrons are emitted into the anode-cathode (a-k) gap. The current addition path in the DPHC forms magnetic ’null’ regions, across which electrons are lost to the anode, shunting current from the inner MITL and load. In experiment, current losses of >10% have been measured within the convolute; this reduces the power delivered to the load, negatively impacting the load performance, as well as complicating the prediction of the Poynting flux used to drive detailed magneto-hydrodynamic (MHD) simulations [2, 3]. In this thesis we develop 3-dimensional (3D) Particle-in-Cell (PIC) and hybrid fluid-PIC computer models to simulate the plasma evolution in the DPHC and inner MITL. The expected experimental current loss at peak current was matched in simulations where Hydrogen plasma was injected from the cathode electrode at a rate of 0.0075mlns−1 (1ml=1015cm−2), with an initial temperature of 3eV. The simulated current loss was driven by plasma penetrating the downstream side of the anode posts, reducing the effective a-k gap spacing and enhancing electron losses to the anode. The current loss at early time (<10MA), was matched in simulations where space-charge-limited (SCL) electron emission was allowed directly from the cathode; to match the loss over the entire current pulse, a delay model is motivated. Here, plasma injection was delayed after the start of SCL emission, based on realistic plasma expansion velocities of ∼3cmμs−1. The PIC model, which was necessary to accurately simulate the kinetic behaviour of the lower density plasma and charged particle sheaths, was computationally intensive such that the spatial resolutions achieved in the 3D simulations were relatively poor. With the aim of reducing the computational overhead, allowing finer spatial resolutions to be accessed, we investigate the applicability of hyBritish Crown Copyright 2012/MOD iii brid techniques to simulating the cathode plasma in the convolute. Our PIC model was both implemented in the resistive MHD code, Gorgon, where part of the plasma was modelled in the single fluid approximation, and extended to include an inertial two-fluid description of the plasma. The hybrid models were applied to the DPHC simulations, the results from which are used to motivate a three component model; here, the densest part of the convolute plasma is modelled using the single fluid MHD approximation, transitioning to a fully kinetic PIC description of the lower density plasma and charged particle sheaths, linked by a two-fluid description. British Crown Copyright 2012/MOD iv c ©Crown Copyright 2012 “This documents consists of or is adapted from material that is the property of the Secretary of State for Defence of the United Kingdom of Great Britain and Northern Ireland. It is furnished in confidence and may not be further copied, used or disclosed, in whole or in part, without the prior written consent of D/IPR, MOD, Abbey Wood, Bristol, BS34 8JH, UK.”
DOI：
10.1088/0004-637x/691/2/l147
发表时间：
2008-11
期刊：
The Astrophysical Journal
影响因子：
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作者：
Andrea Ciardi;S. Lebedev;A. Frank;F. Suzuki-Vidal;G. Hall;S. Bland;A. Harvey-Thompson;E. Blackman;M. M. L. D. Paris-M.;Lerma;France Imperial College;B. Laboratory;U. Rochester;D. Physics;Astronomy;Usa University of Heidelberg;Centre for Astronomy Heidelberg;Germany. Present address Ecole Normale Superieure;Laboratoire de Radioastronomie;France.
通讯作者：
Andrea Ciardi;S. Lebedev;A. Frank;F. Suzuki-Vidal;G. Hall;S. Bland;A. Harvey-Thompson;E. Blackman;M. M. L. D. Paris-M.;Lerma;France Imperial College;B. Laboratory;U. Rochester;D. Physics;Astronomy;Usa University of Heidelberg;Centre for Astronomy Heidelberg;Germany. Present address Ecole Normale Superieure;Laboratoire de Radioastronomie;France.