Configuration Control Experiments in Heliotron J

Heliotron J is a flexible concept exploration facility for the helical-axis heliotron concept, where the bumpiness (�b) is introduced as the third measure to control the neoclassical transport in addition to the helicity and toroidicity. The effects ofb-control on the plasma performance are investigated in Heliotron J from the viewpoints of the fast ion confinement, global energy confinement and Electron-Cyclotron Current Drive (ECCD). The velocity distribution of fast ions generated by Ion-Cyclotron Range of Frequency (ICRF) heating is measured. In a high-�b configuration, higher energy particles are observed for all pitch angles compared to that in a lower-�b configuration. This observation indicates that the high-�b configuration is preferable for the formation and confinement of the fast ions. The bumpiness effect on the global energy confinement for NBI-only plasmas has been investigated. A favorable energy confinement was obtained in the high-�b configurations, which could be attributed to the improvements in the energetic ion confinement in the high-�b configuration. A wide configuration scan shows that the EC driven current strongly depends on the magnetic ripple structure at the EC power deposited position, indicating that the EC driven current is closely related to the electron trapping.