EFFECT OF COLLISIONALITY AND RADIAL ELECTRIC-FIELD ON BOOTSTRAP CURRENT IN THE LARGE HELICAL DEVICE

The bootstrap current decreases in a more highly collisional regime, a nd in stellarator/heliotron it is predicted that a neoclassical curren t component proportional to the radial electric field exists when elec trons and ions belong to different regimes of collisionality. To evalu ate the bootstrap current in stellarator/heliotron in the whole range of collisionality from the collisionless 1/nu to the Pfirsch-Schluter regime, a new connection formula has been proposed. This connection fo rmula has been applied to Large Helical Device (LHD) plasmas in which ions and electrons belong to different collisionality regimes, and fin ite beta MHD equilibria including the bootstrap current have been obta ined. For LHD plasmas such as ECRH (T-i << T-e) in electron root, the bootstrap current with an electric potential twice as high as the elec tron temperature reduces to about 1/5 to 2/3 of that with zero electri c potential. Then, the MHD equilibrium configuration changes significa ntly, depending on collisionality and radial electric field, even for the same beta value of the LHD plasmas.