Psfc/ja-02-17 Electron Bernstein Waves in Spherical Tori

This paper summarizes the theoretical and numerical results we have obtained for the excitation and propagation of electron Bernstein waves in spherical tokamak plasmas. INTRODUCTION In the electron cyclotron range of frequencies the high-β NSTX and MAST plasmas are overdense to the traditional extraordinary X mode and/or the ordinary O mode. For low harmonics of the electron cyclotron frequency, the X and O modes are cutoff at the edge and for high harmonics the plasma is essentially optically thin to these modes. However, for low harmonics, the X mode and the O mode can mode convert to the electron Bernstein waves (EBW) which have no density cutoffs and can propagate into the core of the plasma. From ray tracing analysis we find that EBWs are locally and strongly absorbed at the Doppler shifted electron cyclotron resonance or its harmonics [1]. For spherical tokamak plasmas, the location of the EBW energy deposition is significantly different for excitations on or away from the equatorial plane [1]. EXCITATION AND PROPAGATION OF EBWs The excitation of EBWs is studied in a slab geometry model where the x coordinate is in the direction of the inhomogeneity, y is along the poloidal direction, and z along the toroidal direction. Assuming that the magnetic field is along z, the propagation of waves in an inhomogeneous cold and collisionless plasma is given by K⊥ dEy dx2 + ω2 c2 ( K ⊥ −K2 X − c2 ω2 k ‖K⊥ ) Ey = k‖KXF (1) d dx [ 1 K‖ dF dx ] + ω2 c2 ( 1− c 2 ω2 k2 ‖ K⊥ ) F = ω2 c2 KX K⊥ k‖Ey (2) where F = ik‖Ex − dEz/dx, dF/dx = (ω/c)K‖Ez, c is the speed of light, ω is the wave