Water purification experiments to decompose phenol, acetic acid, and Rhodamine B in water were conducted using a direct contact of gas corona discharge to the water surface. It was shown that O2 was important in the gas phase for the degradation process, and the negative corona showed higher degradation rates than the positive corona. It was found that the organic contaminants can effectively be decomposed by the present method without pH adjustment. The experimental results indicated that there were optimized values in the O2 concentration, the gas resident time above the water, and the cathode−anode gap. It was also indicated that the O2/CO2 mixture showed a higher degradation rate than the O2/N2 mixture for the gas phase. As the degradation mechanism, the uncharged short-lived radicals are considered to be important.

A water purification reactor using direct contact of gas corona discharge with water is developed into a cylindrical-anode wetted-wall reactor. In a modification from the previous plate anode to the present cylindrical anode, it is expected that reactive radicals produced in a plasma region around a wire cathode in a gas phase can efficiently reach the surface of a flowing-water film so that reactive species such as an OH radical can be effectively produced in water. In this study, aqueous phenol was decomposed using the modified reactor to evaluate its efficiency. As a result, the electron efficiency and energetic efficiency of the cylindrical-anode wetted-wall reactor were respectively 2-3 and 3-4 times greater than those of the plate-anode reactors. Furthermore, the activity of the radical-producing plasma in the proposed reactor was 2 orders of magnitude higher than that of the plate-anode reactor. The experiments applying varied water flow rates and discharge currents indicated that the condition that keeps a smooth water surface is important to achieve maximum decomposition efficiency. In addition, it is found that there is an optimized anode radius to attain high decomposition efficiency.

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In the Helicity Injected Spherical Torus device [Nagata et al., Proceedings of the 17th International Atomic Energy Agency Fusion Energy Conference, Yokohama, 1998 (International Atomic Energy Agency, Vienna, 1998) CD-ROM, EXP4/10], internal magnetic field and current density structures of spherical torus (ST) plasmas sustained by coaxial helicity injection (CHI) have been revealed via intensive internal magnetic measurements. The internal magnetic configuration of the ST plasma formed by CHI is in good agreement with the results of numerical equilibrium fitting calculations. The generation of closed poloidal flux of ST has been verified by varying the external toroidal field strength in the same device. Interestingly, the transition of the current profile from hollow to peaked has been observed during the sustainment phase, which could be explained by inductive effects of currents on open field lines winding the central conductor.