Gyrokinetic study of electromagnetic effects on toroidal momentum transport in tokamak plasmas

The effect of a finite beta(e) = 8 pi n(e)T(e)/B-2 on the turbulent transport of toroidal momentum in tokamak plasmas is discussed. From an analytical gyrokinetic model as well as local linear gyrokinetic simulations, it is shown that the modification of the parallel mode structure due to the nonadiabatic response of passing electrons, which changes the parallel wave vector k(parallel to) with increasing beta(e), leads to a decrease in size of both the diagonal momentum transport as well as the Coriolis pinch under ion temperature gradient turbulence conditions, while for trapped electron modes, practically no modification is found. The decrease is particularly strong close to the onset of the kinetic ballooning modes. There, the Coriolis pinch even reverses its direction. (C) 2011 American Institute of Physics. [doi:10.1063/1.3609841]