Bootstrap current control in stellarators

The poloidal coil system of a stellarator can be used to modify the |B| 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 bootstrap current, because the effects of bootstrap current can be eliminated by an appropriate external coil system. The advanced toroidal facility (ATF) [Fusion Technol. 10, 179 (1986)] can be used to test some of these results.