EFFECTS OF FINITE-BETA AND RADIAL ELECTRIC-FIELDS ON NEOCLASSICAL TRANSPORT IN THE LARGE HELICAL DEVICE

The effects of finite beta and radial electric fields on neoclassical transport in LHD are investigated with the Drift Kinetic Equation Solv er (DKES) code. In the finite-P configuration, even orbits of deeply t rapped particles deviate significantly from magnetic flux surfaces. Th us, neoclassical ripple transport coefficients in the finite-beta conf iguration are several times larger than those in the vacuum configurat ion under the same conditions of temperatures and radial electric fiel ds. When the plasma temperature is several kiloelectronvolts, a bifurc ation of the electric fields appears under the ambipolarity condition. The E x B drift due to the resultant sufficiently large radial electr ic fields causes the orbits to curve so that they more closely follow the pressure surfaces and improves significantly the transport coeffic ients in the finite-beta configuration.