Excitation of electron Bernstein waves in spherical tori

Summary form only given. Low aspect ratio spherical tori have many theoretical advantages over the traditional large aspect ratio tokamaks, In particular, one is exploring different plasma regimes, and with the low aspect ratio one has high P with absolute magnetic well and high bootstrap fraction. Because of the high-q/sub /spl psi//, one should have reduced disruptive behavior. Concerning transport in spherical tori, microinstabilities should be reduced because of geometric and flow shear properties. Two proof-of-principle spherical tori online are NIST at Princeton and MAST at Culham. These high /spl beta/ plasmas have /spl omega//sub pe/>>/spl omega//sub oe/ so that neither the O-mode or the X-mode are appropriate for heating or driving non-inductive currents in the plasma core. However, under certain conditions, an externally launched O- or X-mode will undergo efficient mode conversion to electron Bernstein wave (EBW). We examine O-X-EWB conversion for frequencies under consideration for operation in MAST: f=60 GHz and f=28 GHz, and in particular, we estimate the absorbed power at both these frequencies as well as any constraints on required beam alignment and polarization.