Current drive by ion Bernstein waves in tokamaks

Detailed consideration is given to the problem of current drive by ion Bernstein waves (IBWs). An analytical investigation of ray tracing equations is used to prove that a significant evolution of kparallel for the IBWs in tokamaks can ensure the possibility of current drive by these waves, if certain conditions are fulfilled. The main condition is the displacement of the antenna out of the midplane by a proper distance. Several scenarios for current drive are discussed, including direct excitation of the IBWs and the conversion of fast waves into IBWs. In all of these a loop antenna with a symmetrical spectrum in kparallel can be used, the electron distribution function also being symmetrical in Vparallel. The development of asymmetry in kparallel for the IBWs during their propagation is caused by the gradient of the toroidal magnetic field along the major radius. Numerical calculations are also performed - for the cases of ITER and the T-10 tokamak. It is concluded that IBWs can be used as an inexpensive and effective current drive and current density profile control in tokamaks. (author). 26 refs, 9 figs