MODELING OF MEV ALPHA-PARTICLE ENERGY-TRANSFER TO LOWER-HYBRID WAVES

The interaction between a lower hybrid wave and a fusion alpha particl e displaces the alpha particle simultaneously in space and energy. Thi s results in coupled diffusion. Diffusion of alphas down the density g radient could lead to their transferring energy to the wave. This coul d, in turn, put energy into current drive. An initial analytic study w as done by Fisch and Rax. Here we calculate numerical solutions for th e alpha energy transfer and study a range of conditions that are favou rable for wave amplification from alpha energy. We find that it is pos sible for fusion alpha particles to transfer a large fraction of their energy to the lower hybrid wave. The numerical calculation shows that the net energy transfer is not sensitive to the value of the diffusio n coefficient over a wide range of practical values. An extension of t his idea, the use of a lossy boundary to enhance the energy transfer, is investigated. This technique is shown to offer a large potential be nefit.