Generation of hot spots by fast electrons in lower hybrid grills

Generation of hot spots on plasma facing components magnetically connected to the grill is a main limiting factor in high-power operation of a lower hybrid system. A possible explanation for the hot spots is the sputtering caused by fast electrons generated by parasitic absorption of lower hybrid power near the grill mouth. The behavior of the edge plasma near the grill mouth is investigated with a new tool in this context: the self-consistent particle-in-cell (PIC) code XPDP2 [V. Vahedi et al., Phys. Fluids B 5, 2719 (1993)]. The PIC simulations provide the key parameters of the problem: the absorbed power, the radial deposition profiles, and the energy spectrum of the accelerated particles close to the grill.