Surface erosion models for liquid lithium inside the DIII-D tokamak*

Investigating the feasibility and benefit of retrofitting DIII-D with a liquid lithium (Li) divertor will address research gaps in liquid metal plasma-facing components. By using predictive modeling with the SOLPS-ITER boundary plasma code package, used previously for elements like carbon, and custom Li surface models based on previous literature [1], estimates of Li erosion and leakage into the plasma core are made using Python based models. Li is favored for its low z and heat flux capacity. Its surface coverage and plasma heating power vary to identify configurations that optimize heat flux handling and minimize dilution. The strengths, limitations, and impact of different sputtering models/databases on the simulation will be assessed.  The temperature of the Li divertor, which is fed into the surface model, is estimated as a function of the deposited power density by using a 1D transient thermal code written in MATLAB. It computes the temporal evolution of the temperature in the Li divertor including the melting and evaporation phase changes, so that evaporative cooling and thus Li surface temperature locking can be accounted for in the model. Adding current models of Li erosion as a function of wall temperature to the code package is expected to improve predictions of the achievable parameter space for a liquid Li divertor in DIII-D.

[1] T. Abrams et al., Nucl. Fusion 56 (2016) 016022