Formation and Confinement of High-Energy Ions in Heliotron J

A fast-ion formation and confinement experiment is performed using the ion cyclotron range of frequencies (ICRF) minority heating scheme in Heliotron J. In particular, the role of one of the Fourier components, the bumpiness, is an important issue for the design principle of the magnetic field of Heliotron J, where the particle confinement is controlled by the bumpiness. We study the dependence of the fast-ion confinement on the bumpiness using fast ions produced by the ICRF heating.

High-energy ions are produced up to 10 keV by injecting an ICRF pulse into electron cyclotron heating target plasmas. Moreover, ions up to 36 keV are observed in the combination heating of ICRF and neutral beam injection (NBI), where the NBI energy is 28 keV. To clarify the role of the bumpy component for the high-energy ions, three configurations with various bumpy components are selected. The tail temperature is highest in the high bumpy case. It is considered that bumpy control is effective for the fast-ion confinement in Heliotron J. An increase of the bulk-ion temperature from 0.2 to 0.4 keV is observed during the ICRF pulse. The heating efficiency also depends on the bumpy component.