Mode conversion coupling to electron Bernstein waves

In NSTX, and generally in spherical tori, the emission of electron Bernstein waves (EBW) from the interior of the plasma can be observed in the vacuum region after mode conversion to the X mode and/or the O mode. The same mode conversion process comes into play when exciting EBWs through externally launched power. We consider the mode conversion process that couples the O mode to EBWs via the X mode. It is shown that density inhomogeneity can change the mode conversion efficiency significantly from that obtained analytically in [1]. Results obtained from a comprehensive model [2] are found to differ from the analytical result as the gradient scale length decreases. A detailed analysis comparing the analytical and computational results will be presented. \newline [1] E.\ Mj{\o}lhus, {\it J.\ Plasma Phys} {\bf 31}, 7 (1984). \newline [2] A.\ K.\ Ram and S.\ D.\ Schultz, Phys.\ Plasmas {\bf 7}, 4084 (2000).