Effect of net direct current on the properties of radio frequency sheaths: simulation and cross-code comparison

The accompanying files contain digital data for figures in the article "Effect of net direct current on the properties of radio frequency sheaths: simulation and cross-code comparison" by J. R. Myra, M.T. Elias, D. Curreli, and T. G. Jenkins, submitted to the journal Nucl. Fusion. Abstract In order to understand, predict and control ion cyclotron range of frequency (ICRF) interactions with tokamak scrape-off layer plasmas, computational tools which can model radio frequency (RF) sheaths are needed. In particular, models for the effective surface impedance and DC rectified sheath potentials may be coupled with full wave RF simulation codes to predict self-consistent wave fields near surfaces and the resulting power dissipation and plasma-material interactions from ion sputtering. In this study, previous work assuming zero net DC current flow through the sheath is generalized to allow the surface to collect net positive or negative current, as is often observed in experiments. The waveforms, DC potential and RF admittance are investigated by means of analytical theory, nonlinear fluid and particle-in-cell (PIC) codes. Cross-code comparisons provide detailed model verification and elucidate the roles of ion and electron kinetics. When the sheath draws negative (positive) DC current, the voltage rectification is reduced (increased) compared with the zero-current case, and both the real and imaginary parts of the admittance are increased (reduced). A previous four-input parametrization of the sheath rectification and admittance properties is generalized to include a fifth parameter describing the DC sheath current.随附文件包含J. R. Myra、M.T. Elias、D. Curreli与T. G. Jenkins提交至《Nucl. Fusion》期刊的论文《净直流对射频鞘层特性的影响：模拟与多代码比对》（原英文标题：Effect of net direct current on the properties of radio frequency sheaths: simulation and cross-code comparison）各配图的数字数据。 摘要：为理解、预测并调控离子回旋频段（ion cyclotron range of frequency, ICRF）与托卡马克刮削层等离子体的相互作用，亟需可模拟射频（radio frequency, RF）鞘层的计算工具。具体而言，有效表面阻抗与直流整流鞘层电势的模型可与全波射频模拟代码耦合，以预测近表面的自洽波场，以及由离子溅射引发的功率耗散与等离子体-材料相互作用。本研究将此前假设鞘层无净直流电流流过的工作推广至允许表面收集净正或净负电流的情形——该情形在实验中较为常见。本文通过解析理论、非线性流体模型与粒子网格（particle-in-cell, PIC）代码，对波形、直流电势及射频导纳展开研究。多代码比对可实现模型的详细验证，并阐明离子与电子动力学的作用机制。当鞘层汲取负（正）直流电流时，相较于零电流工况，电压整流效应会减弱（增强），且导纳的实部与虚部均会升高（降低）。此前针对鞘层整流与导纳特性的四输入参数化模型被拓展，新增了描述直流鞘层电流的第五个参数。