Effects of Magnetic Islands Produced by External Perturbation Fields in the Tohoku University Heliac

Abstract

Island effects on the plasma periphery due to the external perturbation fields in the Tohoku University Heliac (TU-Heliac) were surveyed. A fixed m = 3 magnetic island was produced by two pairs of external cusp field coils. The electron density decayed from the outer edge of the island after perturbation field application. Radial profiles of the electron temperature and plasma space potential in the island region revealed the magnetic island structure. The radial electric field at the inner edge of the island increased after perturbation field application. The positions of local maxima in the plasma space potential profile were in good agreement with the position of the n/m = 5/3 rational surface. The potential profile in the island grew with the perturbation field strength. The full width at half maximum of the potential profile depended on the square root of the perturbation field coil current.