Theory of ion Bernstein and lower hybrid waves synergy

The synergistic behavior of a lower hybrid wave (LHW) and an ion bernstein wave (IBW) on the PBX-M tokamak is theoretically investigated on the basis of a quasilinear model. The analytical approach to this investigation is oriented to solve simultaneously, the 2D ray tracing equation for both waves, to reconstruct the WKBJ electric field and the quasilinear diffusion coefficient. The Fokker-Planck equation for the 2-D distribution function is numerically solved and coupled to the ray tracing in the calculation of the absorption. A numerical code which solves the ray tracing equations and calculates the 2 D (v parallel, v perpendicularto) distribution function has also been run to compare the results with the analytical one. The numerical and analytical results are compared with the experimental observations obtained by a 2-D hard X-ray (HXR) camera. The camera measures the bremsstrahlung emission from fast electrons on the tail of the distribution function. Experimentally, when IBW is injected in a plasma during LHCD, there is a strong increase in the HXR emission with respect to the signal detected with LHW alone. This increase appears to be predominantly localized off-axis. This phenomenology can be correlated with the Landau damping of the LHW power on the tail of the electron distribution function modified by IBW. (orig.)