Bootstrap current in optimized stellarators

This work examines bootstrap current and its impact on the equilibrium properties in optimized stellarators. Two independent methods are used to calculate the bootstrap current: a fast code based on a calculation in an asymptotically collisionless limit [K. C. Shaing, {\it et al.}, Phys. Fluids B {\bf 1}, 148 (1989)] and a fluid moments approach that self- consistently calculates the neoclassical transport coefficients, including the bootstrap current [D. A. Spong, Phys. Plasmas {\bf 12}, 056114 (2005)]. The bootstrap current calculations from the two codes were done for low density, ECH-heated and high density, ICH-heated plasmas. In the configurations examined here, namely, the Quasi-Poloidal Stellarator (QPS), the National Compact Stellarator Experiment, the Helically Symmetric Experiment (HSX), the Large Helical Device, and the Wendelstein- 7X Stellarator (W7-X), the bootstrap currents predicted from the two codes agree qualitatively for both ICH and ECH profiles. A self-consistent bootstrap current results in a negligible increase in the rotational transfrom for W7-X, an increase in the rotational transform for QPS, and a larger decrease in the rotational transform for HSX.