Study of plasma formation within the electrostatic residual ion dump proposed for the HNB injectors of ITER

Abstract

The electrostatic residual ion dump (ERID) concept, proposed as the reference RID design for the neutral beam system of ITER, represents an alternative to more conventional magnetic RID devices, with respect to which has some advantages. However, the removal of the ions emerging from the neutralizer of the neutral beam injectors by means of the ERID device presents some problematic issues, concerning, for instance, the power load suffered by the ERID panels, the deuterium recycling processes inside its channels and the possible formation of a plasma. The last one might be particularly critical, since the creation of a plasma would modify the deflection properties of the device, and therefore would affect its proper functioning. In this respect, we present a study of the ERID performances. The results obtained show that the peak power load is lower than about 8 MW m−2, which is admissible from a thermo-mechanical point of view. Moreover, the contribution due to the deuterium outgassing appears to be smaller than the value of the residual background gas. Finally, the estimated ionization density rate is tiny compared with the critical threshold for the production of a plasma inside the ERID.