Plasma sputtering erosion/redeposition in fusion tokamaks—Modeling status and challenges

Plasma/material (PMI) interactions is the most critical engineering issue for fusion power development. Key concerns include the lifetime of plasma facing components (PFC´s) due to steady state sputter erosion, plasma contamination by eroded material, tritium codeposition in redeposited material, and plasma operating limits due to these factors. Present tokamaks use primarily low-Z (Be, C) and high-Z (Mo, W) solid materials for PFC surfaces, and to some extent solid and liquid Li. These are acceptable given existing plasma regimes. The ITER PFC design (Be wall, W divertor) is predicted to work, e.g. [1], but the wall acceptability is due to the low (~3%) duty factor. Future commercial tokamaks will likely require a high-Z wall, and a high-Z or flowing liquid metal divertor, and plasma edge parameters in the right operating window. It is critical to the design and operation of future devices that we have detailed, predictive modeling of the plasma/material interactions. Most erosion/redeposition analysis has been done with the REDEP/WBC code package, e.g. [2], with associated plasma and material response inputs from codes and data. Such plasma inputs, for example, include convective edge plasma regime energy and particle boundary fluxes, while recent surface material modeling has dealt with time-dependent mixed-material formation and response. Analysis and code/data validation show generally good comparisons for PFC gross and net sputtering erosion, and sputtered impurity transport, in current tokamaks, e.g., NSTX, DIII-D, C-MOD. However, major work is needed in multi- code coupling/super-computing development, and with focused PMI experiments. I review the general sputtering erosion science issues, code/data validation status, analysis for prospective tokamak power reactors, and challenges for predictive modeling.