April 4-6

Abstract Details

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Author: David N. Smithe
Requested Type: Poster
Submitted: 2022-03-04 12:52:51

Co-authors: Tom Jenkins, Matt Poulos, John Wright, Jim Myra

Contact Info:
Tech-X Corporation
5621 Arapahoe Ave.
Boulder, CO   80303

Abstract Text:
We present results from a validity benchmark study of the VSim/Vorpal software's RF sheath model. We compare to published results from Kohno [1], and to new benchmark cases developed recently as part of a wider benchmarking effort [2]. Some of these cases allow for multiple frequency-domain solutions, due to the non-linearity of the problem, and to the presence of surface plasma waves. The time domain approach provides a way to resolve such cases, with the observed behavior seen when approaching these situations with reasonable transients sometimes being a long base-line beating between allowed solutions rather than rapid selection of a single solution state.
The RF sheath algorithm in VSim/Vorpal augments the software's cut-cell PEC model, and we also benchmark the algorithm for computational variation such as size of cut-cell and slope of surface relative to the computational mesh.
Finally, we show application of the model to fully 3D geometry typical of ICRF and helicon launchers in tokamak experiments, and show how the RF voltages are used to compute rectified DC sheath voltages that may lead to impurity production.

Work supported by DOE Grant DE-SC0018319 (RF SciDAC) and DE-SC0017843 (Phase II SBIR).

[1] "Radio-frequency wave interactions with a plasma sheath in oblique-angle magnetic fields using a sheath impedance model," H. Kohno and J. R. Myra, Physics of Plasmas 26, 022507 (2019).

[2] Multirootparameters.pdf, by Matt Poulos. Also see poster by Matt Poulos, this conference.