Fluctuations and stability of plasmas in the H-1NF heliac

The H-1NF heliac is a medium-sized heliac stellarator experiment with major radius R = 1 m, average plasma minor radius a = 0.15-0.2 m. Its 'flexible-heliac' coil set permits extraordinary variation in the rotational transform profile and magnetic well. Experiments in low-field (B < 0.2 T) argon plasmas heated by helicon waves have yielded fundamental results on turbulent transport and confinement transitions, in particular concerning non-ambipolar flows, electric fields, and zonal flows. At higher field, (0.5 T), the device can be operated with precise (<1%) control of the rotational transform profile. Configuration scans with H-He plasmas heated by up to 100 kW of ICRF show resonance phenomena in confinement that correlate with changes in the characteristics of coherent magnetic field fluctuations. (author)