Results obtained in the initial experimental phase of Heliotron J are reported. Electron beam mapping of the magnetic surfaces at a reduced DC magnetic field has revealed that the observed surfaces are in basic agreement with the ones calculated on the basis of the measured ambient field around the device. For 53.2 GHz second harmonic ECH hydrogen plasmas, a fairly wide resonance range for breakdown and heating by the TE02 mode has been observed in Heliotron J as compared with that in Heliotron E. With ECH injection powers up to ≈ 400 kW, diamagnetic stored energies up to ≈ 0.7 kJ were obtained without optimized density control.

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A broad mixed ion beam containing positive ions of gallium (Ga) was produced with a plasma sputter-type ion source. Liquid Ga was suspended on a tungsten reservoir to be sputtered and postionized in argon (Ar) plasma excited by a radio frequency (rf) power at 13.56 MHz. Optical emission spectra from the plasma near the Ga sputtering target had indicated that the release of Ga into plasma increased with increasing negative bias to the sputtering target. The ratio of Ga(+) current to Ar(+) current was measured to be about 1% with a quadrupole mass analyzer at 100 V extraction voltage for incident rf power as low as 30 W. Ions in the plasma were extracted through a pair of multiaperture electrodes. The homogeneity of Ga flux was examined by making a Ga deposition pattern on a glass substrate located behind the extractor electrodes.

Studies of global energy confinement and toroidal plasma current behaviour for the second harmonic 70 GHz ECH at B = 1-1.5 T are described with emphasis on the magnetic configuration effects in the helical-axis heliotron 'Heliotron J'. At low densities of ne < 0.4×10 19 m −3 , the electron temperature reached T e ≈ 1 keV in the core region, indicating the production of collision-less plasmas of electron collisionality ν * 0.1, where ν * = ν/(v e /π R 0 q). For medium densities of 0.5 × 10 19 m −3 < ne < 2 × 10 19 m −3 , the preferable energy confinement time, 1.5-2 times larger than that of the ISS95 scaling, was obtained under the condition of localized central heating at B ≈ 1.25 T for the standard configuration of Heliotron J. The measurements of the toroidal current under perpendicular microwave injection revealed the change of the current flow direction as a function of the poloidal magnetic field. The measured current behaviour was found to be qualitatively consistent with that of the bootstrap current predicted from neoclassical theory. The observed flow reversal showed that a proper selection of the field configuration could control the bootstrap current in the helical-axis heliotron. In addition, the current control through the electron cyclotron current drive scenario with oblique injection of microwaves was experimentally examined.