Simulation of Deuterium Retention in Tungsten Exposed to Divertor Plasmas

Abstract

To study tritium retention in a divertor target made of tungsten, thermal processes of hydrogen isotopes, including implantation, diffusion, trapping and detrapping, and surface recombination, are modeled for ITER plasma configuration. The material parameters governing the processes are estimated by simulating an existing TDS experiment by using the model. In case of the inner target, dominant retention mechanism is the trapping in the deep trap and most of the T atoms are kept in the trap even after discharge. Mobile T atoms dominate the T retention in the outer target due to its high temperature, the amount of which is ten times greater than that in the inner target. The T retention after a discharge of 400 s is estimated to be tens of mg, resulting in 10000 or more discharges after which a T safety limit of 700 g is reached. Nevertheless, it strongly depends on the trap concentration in the target.