Helium ash removal by moving-surface plasma-facing components

The use of moving-surface plasma-facing components (MS-PFCs) is proposed for the removal of helium ash as well as unburned hydrogenic fuel particles from steady state DT-fusion reactors. A series of proof-of-principle experiments have been conducted, using the VEHICLE-1 facility in which a rotating drum, the simplest form of MS-PFC, can be bombarded with steady state hydrogen, helium and their mixture plasmas with the densities of the order of 1010 cm−3 and the electron temperatures of 4–5 eV. It has been found from Hα and He–I spectroscopic measurements that the steady state particle removal rates are ∼2.5 × 1016 H-atoms s−1 cm−2 and ∼1.6 × 1014 He-atoms s−1 cm−2 when the rotating drum is gettered with lithium at the deposition rate of ∼2 × 1016 Li-atoms s−1 cm−2 and negative bias voltages of −30 V and −100 V. These data correspond to the average atomic ratios of H/Li ∼ 1.25 and He/Li ∼ 0.008 in the resultant codeposits. It follows from these findings that hydrogen and helium are not mutually exclusive in the simultaneous codeposition processes, presumably because of their respective preferred trapping sites in lithium deposits.