Validated modeling of plasma boundary physics coupled to surface response for atmospheric arcs*

Plasma boundary physics for tokamak divertors and atmospheric arcs have a lot of similarities: both require analysis of the heat and particle fluxes coupled to the surface response in the walls or electrodes mitigated by the space-charge sheaths modified by the electron and neutral emission from the surfaces. Resulting nonlinear equations for the plasma profiles are substantially complex and difficult to solve. We have developed several codes in multi-dimensions and verified each code against other to remove unavoidable bugs. Additional verification was performed against specially derived nonlinear analytical solution in the boundary layer where an approximate invariant of combination of density and temperature gradients was found [1]. In order to validate the predictions of the model, ablated species profiles and ablation rates of the wall material were compared with the measured experimental data in our Nanolab [2] and are in a good agreement, though some observed differences require further investigation.

[1] A. Khrabry, et al., Phys. Plasmas 25, 013521 and 013522 (2018).

[2] https://nano.pppl.gov/

V. Vekselman, et al.,  Plasma Sources Sci. T. 27, 025008 (2018).