On plasma rotation induced by traveling fast Alfven waves

Absorption of fast Alfven waves by the minority fundamental ion-cyclotron resonance, coupled with finite banana width physics, generates torque distributions, and ultimately rotational shear layers in the bulk plasma, even when the toroidal wave number k(phi)=n/R of the fast wave vanishes (n=0) and cyclotron absorption introduces no angular momentum nor canonical angular momentum [F. W. Perkins, R. B. White, P. T. Bonoli, and V. S. Chan, Phys. Plasmas 8, 2181 (2001)]. The present work extends these results to traveling waves with nonzero n where heating directly introduces angular momentum. Since tokamak fast-wave antennas have approximately one wavelength per toroidal field coil, the toroidal mode number n lies in the range n=10-30, independent of machine size. A zero-dimensional analysis shows that the rotation rate arising from direct torque is comparable to that of the rotational shear layer and has the same scaling. Nondimensional rotation profiles for n=(-10, 10) show modest changes from the n=0 case in the expected direction. For a balanced antenna spectrum, the nondimensional rotational profile (averaged over n=-10, 10) lies quite close to the n=0 profile. (C) 2002 American Institute of Physics.