Validation of prompt versus local tungsten redeposition using target geometry and magnetic field scans

Using the 3D Monte-Carlo Global Impurity TRansport (GITR) code, we examine differences in the redeposition pattern for tungsten (W) surfaces with a particular view toward ex situ diagnostic methods for discriminating the dominating redeposition mechanisms. Our modeling results show that W redeposition is primarily geometrically-driven (promptly redeposited) or electrostatically-driven (locally transported within the pre-sheath). We have demonstrated how the dominant redeposition type evolves under changes in key plasma parameters and present initial modeling results comparing W redeposition mechanisms in different magnetic field strengths (i.e., 0.7T and 2.2T, corresponding to future experiments planned at CTH and DIII-D, respectively). The distinction in redeposition mechanism is inferred using exact patterning of the source isotopic W which provides sub-mm spatial accuracy of the resultant deposition. By scanning target geometries as well sheath conditions, the GITR redeposition patterns show distinct spatial regions for sputtered material that is geometric- versus electrostatic-driven. These techniques lay the foundation for determining these mechanisms experimentally and for comparing ex situ with in situ diagnostics, all to provide better predictive high-Z sputtering models.