Effect of collisionality and radial electric field on bootstrap current in the Large Helical Device

Abstract

The bootstrap current decreases in a more highly collisional regime, and in stellarator/heliotron it is predicted that a neoclassical current component proportional to the radial electric field exists when electrons and ions belong to different regimes of collisionality. To evaluate the bootstrap current in stellarator/heliotron in the whole range of collisionality from the collisionless 1/ν to the Pfirsch-Schluter regime, a new connection formula has been proposed. This connection formula has been applied to Large Helical Device (LHD) plasmas in which ions and electrons belong to different collisionality regimes, and finite beta MHD equilibria including the bootstrap current have been obtained. For LHD plasmas such as ECRH (T1 << Te) in electron root, the bootstrap current with an electric potential twice as high as the electron temperature reduces to about 1/5 to 2/3 of that with zero electric potential. Then, the MHD equilibrium configuration changes significantly, depending on collisionality and radial electric field, even for the same beta value of the LHD plasmas