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Simulating the effect of improved PMI models with SOLPS

Author: John M. Canik
Requested Type: Poster Only
Submitted: 2015-02-02 17:42:05

Co-authors: X. Tang

Contact Info:
Oak Ridge National Laboratory
P.O. Box 2008-6169
Oak Ridge , TN   37831
USA

Abstract Text:
2D fluid transport simulations using the SOLPS suite of codes have been used to evaluate recent physics improvements in several aspects of the plasma-materials interface, enabled by advanced computations. New molecular dynamics simulations have shown that fast particle and energy reflection coefficients on tungsten surfaces are significantly higher than previously assumed based on calculations using the binary collision approximation. The updated energy reflection factors can approach unity under some conditions. Further, recent particle-in-cell simulations of the plasma sheath have shown significantly different values for the sheath heat transmission coefficients than are typically assumed within SOLPS, with similar values for the total transmission but a near reversal of the ion and electron contributions. These improved values for reflection and the sheath boundary conditions have been incorporated into SOLPS, which is then used as a test bed to evaluate the impact on the global plasma solution. It is found that high reflection coefficients lead to an increase in the scrape-off layer and divertor plasma temperature. The ion power loss is largely carried back as fast neutrals, which then transfer energy via charge exchange collisions with the plasma. Under these conditions, the electrons must exhaust most of the input power, resulting in a significant increase in temperature. At low plasma density, the new sheath transmission coefficients show a strong impact on the divertor temperatures, with electron and ion temperatures increasing and decreasing, respectively. However, at high densities the effect is reduced due to the strong energy coupling between electrons and ions. The impact of the new PMI models on access to high density, low temperature divertor regimes and overall implications for machine operation will be discussed. Supported by the US DOE under DE-AC05-00ER22725 and DE-AC52-06NA25396, as part of the SciDAC project on Plasma-Surface Interactions.

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