Stabilization of resistive wall modes (RWMs) is one of the important issues in magnetic fusion research. In the reversed field pinch (RFP), the number of unstable RWMs becomes smaller by lowering the aspect ratio (A), the ratio of the minor to major radius of the device. In REversed field pinch of Low-Aspect ratio eXperiment (RELAX), whose aspect ratio is 2, unstable m/n = 1/2 RWM was stabilized by a single mode control power supply system with improvements of discharge performance. In this paper we report new results with modified power supply system in which magnetic boundary condition near the poloidal gaps is controlled. The modified power supply system is designed to stabilize the most unstable m/n = 1/2 mode by use of the saddle coil array covering the whole torus with eight (8) power supplies. The results show that the discharge duration is improved from ∼ 3.0 ms to ∼ 4.0 ms, limited by the capability of the iron core in RELAX device. Stabilization of the dominant RWM with the resultant improved plasma performance by a single mode control power supply system shows one of the advantages of a low-aspect-ratio RFP concepts.

Atmospheric pressure plasma jets are useful tools in biology and environmental engineering. However, when a needle electrode configuration is employed to generate argon plasma, the electrode temperature often exceeds 150°C, and the plasma irradiation time is limited. In this study, it was possible to suppress the electrode temperature increase during plasma discharge and irradiate plasma for a long time by covering the ground electrode with insulating oil. The number of radicals generated in water by the plasma jet was also examined via color change of a polyvinyl alcohol-potassium iodide solution.

Fe flake was fabricated by ball-milling, and frequency dependences of permeability and noise suppression of resin composite with Fe flake were investigated. The aspect ratio of Fe flake increased with increasing ball-milling time (t_m), and the highest aspect ratio was 43 after ball-milling for t_m=12 h. Frequency dependence of imaginary part of complex permeability for resin composite with Fe flake had two inflection points (f₁, f₂) related to the domain-wall resonance and natural resonance. Noise suppression properties of resin composite with Fe flake was higher than that of resin composite with spherical powder, and the noise suppression property had a peak close to f₂.