DIFFUSION OF THERMONUCLEAR ALPHA-PARTICLES UNDER THE INFLUENCE OF INTENSE LH WAVES

Recently, a new mechanism was proposed by Fisch and Rax which should l ead to amplification of lower hybrid (LH) waves at the expense of alph a particles energy, improving thus the LR current drive efficiency. Th e present contribution investigates the possibility of achieving the c onditions on which this mechanism - based on the spatial diffusion of fusion alpha particles - could become operative. The analysis performe d shows that in reactor grade tokamaks, the penetration of LH waves in to the plasma column is very poor due to the intense electron Landau d amping and the complicated geometry of the equilibrium magnetic fields . Consequently, at acceptable LHW input power levels, the waves do not reach the regions where fusion alpha particle power could reasonably compensate the losses of LHW energy due to the damping by electrons. T he model of Fisch and Rax is based on special features of the induced diffusion of alpha particles in the energy-configuration space. Using suitable Hamiltonian formalism, the LHW induced radial diffusion of al pha particles and the energy transport between LHW and alpha particles in the frame of generalized quasilinear Lines of diffusion constraint is also investigated. A rather strong change of k(parallel to) of LHW along the ray trace can contribute to the change of energy transport between LHW and alpha particles as well.