Bootstrap current control and the effects of the radial electric field in stellarators

The effects of the radial electric field E/sub r/ on the bootstrap current in ATF-type configurations are studied with the Drift Kinetic Equation Solver (DKES). It is found that there is a range of E/sub r/ values over which the bootstrap current does not depend on E/sub r/. The effects of E/sub r/ on the bootstrap current are due to the resonance between the parallel velocity and the poloidal E /times/ B drift. The poloidal coil system of a stellarator can be used to modify the /vert bar/B/vert bar/ spectrum and, as a consequence, change the magnitude of the bootstrap current. The addition of a small l = 1 field component to a stellarator field can cancel or reverse the direction of the bootstrap current. It is shown that currentless operation in the collisionless regime is not impaired by the bootstrap current, because the effects of the bootstrap current can be eliminated by an appropriate external coil system. These results can be tested in ATF. 15 refs., 11 figs.