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

J. R. Myra, M. T. Elias, D. Curreli, T. G. Jenkins

Research output: Contribution to journalArticlepeer-review

Abstract

In order to understand, predict and control ion cyclotron range of frequency 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 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 the magnitude of 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.

Original languageEnglish (US)
Article number016030
JournalNuclear Fusion
Volume61
Issue number1
DOIs
StatePublished - Jan 2021

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Condensed Matter Physics

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