Studies of the confinement and the toroidal current control in Heliotron J

The plasma confinement properties of Heliotron J plasmas and the toroidal current are investigated. A plasma energy of 2.5 kJ has been achieved by 70 GHz-0.35 MW electron cyclotron heating (ECH). The energy confinement time is within the expected values as determined by the stellarator scaling law. In the high density region, however, better confinement plasmas are observed. The transition phenomena characterized by Hα signal drop are sometimes observed in such a region. The toroidal current generally affects plasma confinement since it generates a poloidal magnetic field. From this point of view, toroidal current control is studied in terms of field-component variation and electron cyclotron current drive. The zero current condition is found in the inner vertical field scan. Current control using the electron cyclotron wave is also demonstrated. (author)