Effects of electromagnetic turbulence in the neoclassical Ohm's law

An Ohm's law for tokamak plasmas has been derived, which includes the effect of electromagnetic turbulence as well as the neoclassical conductivity and bootstrap current. The most important current-driving effects of the turbulence have been identified, expressions for the driven (dynamo) current have been derived and these have been evaluated using the GYRO electromagnetic turbulence code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)]. The most important current drive mechanism, the divergence of the radial flux of parallel electron momentum induced by magnetic flutter, drives a current density which has positive peaks on low order rational surfaces, with compensating negative dips nearby, thus driving zero total current. Another current drive mechanism, the beating of the parallel electric field fluctuations with the electron density fluctuations, drives a current density which is much smaller than that driven by the magnetic flutter mechanism, but could drive a nonzero total current. (C) 2004 American Institute of Physics.