Experiment of magnetic island formation in Large Helical Device

摘要

Magnetic island formation is experimentally investigated in the Large Helical Device. The (m, n) = (1, 1) vacuum magnetic island is generated by using the local island diverter field, where m and n are the poloidal and toroidal mode numbers, respectively. The island width depends on plasma parameters (the electron temperature and the beta) and the magnetic axis position. In the case of R-ax = 3.53 m the magnetic island in the plasma is larger than that in the vacuum field. Here, R-ax is the major radius of the magnetic axis. In the case of R-ax = 3.6 m the magnetic island is not generated when the error field is less than the threshold which is increased as the beta is increased. Evidence of island current is obtained when the magnetic island is formed due to a small error field. However, the mechanism that generates the island is not yet known.