MODELLING VACUUM ARCS: FROM PLASMA INITIATION TO SURFACE INTERACTIONS
MODELLING VACUUM ARCS: FROM PLASMA INITIATION TO SURFACE INTERACTIONS
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真空弧建模：从等离子体引发到表面相互作用
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
H. Timko
中科院分区：
文献类型：
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作者：
H. Timko
更好地了解真空电弧是当今许多“大科学”项目的需要，包括直线对撞机，聚变装置和卫星系统。对于紧凑型直线对撞机（CLIC）的设计，发生在加速腔的射频（RF）故障影响效率优化和降低成本的问题。在定义明确且可重复的直流（DC）条件下，从理论和实验两方面研究真空电弧是探索RF击穿的第一步。在这篇论文中，我们研究了铜直流真空电弧与实验相结合，电弧等离子体的粒子在细胞（PIC）模型，和随后的表面损伤机制的分子动力学（MD）模拟。我们还开发了2D ARC-PIC程序和物理模型，特别是为了模拟真空电弧中的等离子体引发。假设最初在阴极处存在场致发射体，我们已经确定了等离子体形成的条件，并研究了从场致发射阶段到充分发展的电弧的过渡。等离子体的“立足点”是阴极点，它为电弧连续提供粒子;等离子体的高密度核心位于阴极点上方。我们的研究结果表明，一旦电弧等离子体被启动，只要能量是可用的，电弧是自我维持由于等离子体鞘层，确保增强的场发射和溅射。等离子体模型已经可以估计击穿时间如何随中性蒸发速率而变化，这还有待于通过原子模拟来确定。由于问题的非线性，我们还进行了代码到代码的比较。使用独立代码的等离子体行为和击穿时间的再现性增加了此处所示结果的置信度。我们的MD模拟确定了高通量，高能量离子轰击作为一个可能的机制，形成早期的表面损伤真空电弧。在这种机制中，溅射主要发生在集群中，作为重叠的热峰的结果。不同大小的实验和模拟陨石坑被发现是自相似的陨石坑深宽比约为0.23（sim）- 0.26（exp）。
A better understanding of vacuum arcs is desirable in many of today’s ‘big science’ projects including linear colliders, fusion devices, and satellite systems. For the Compact Linear Collider (CLIC) design, radio-frequency (RF) breakdowns occurring in accelerating cavities influence efficiency optimisation and cost reduction issues. Studying vacuum arcs both theoretically as well as experimentally under well-defined and reproducible direct-current (DC) conditions is the first step towards exploring RF breakdowns. In this thesis, we have studied Cu DC vacuum arcs with a combination of experiments, a particle-in-cell (PIC) model of the arc plasma, and molecular dynamics (MD) simulations of the subsequent surface damaging mechanism. We have also developed the 2D ARC-PIC code and the physics model incorporated in it, especially for the purpose of modelling the plasma initiation in vacuum arcs. Assuming the presence of a field emitter at the cathode initially, we have identified the conditions for plasma formation and have studied the transitions from field emission stage to a fully developed arc. The ‘footing’ of the plasma is the cathode spot that supplies the arc continuously with particles; the high-density core of the plasma is located above this cathode spot. Our results have shown that once an arc plasma is initiated, and as long as energy is available, the arc is selfmaintaining due to the plasma sheath that ensures enhanced field emission and sputtering. The plasma model can already give an estimate on how the time-to-breakdown changes with the neutral evaporation rate, which is yet to be determined by atomistic simulations. Due to the nonlinearity of the problem, we have also performed a code-to-code comparison. The reproducibility of plasma behaviour and time-to-breakdown with independent codes increased confidence in the results presented here. Our MD simulations identified high-flux, high-energy ion bombardment as a possible mechanism forming the early-stage surface damage in vacuum arcs. In this mechanism, sputtering occurs mostly in clusters, as a consequence of overlapping heat spikes. Different-sized experimental and simulated craters were found to be self-similar with a crater depth-to-width ratio of about 0.23 (sim) – 0.26 (exp).
影响因子：
2.2
作者：
G. Falchetto;B. Scott;P. Angelino;A. Bottino;T. Dannert;V. Grandgirard;S. Janhunen;F. Jenko;S. Jolliet;A. Kendl;B. Mcmillan;V. Naulin;A. Nielsen;M. Ottaviani;A. Peeters;M. Pueschel;D. Reiser;T. Ribeiro;M. Romanelli
通讯作者：
G. Falchetto;B. Scott;P. Angelino;A. Bottino;T. Dannert;V. Grandgirard;S. Janhunen;F. Jenko;S. Jolliet;A. Kendl;B. Mcmillan;V. Naulin;A. Nielsen;M. Ottaviani;A. Peeters;M. Pueschel;D. Reiser;T. Ribeiro;M. Romanelli