Microwave Plasma Torch at a Water Surface

摘要

An argon plasma torch sustained by a 2.45-GHz electromagnetic wave can be in contact with a water surface or can penetrate inside the water, depending on the wave power. The propagation of the electromagnetic wave sustaining the discharge in water is problematic because the water relative dielectric permittivity greatly depends on the wave frequency and the temperature and varies between 6 and 86. At a wave frequency of 2.45 GHz and room temperature (20°C) the dielectric permittivity is 80, which leads to the very fast decay of the electromagnetic wave. We have studied both theoretically and experimentally the plasma properties and the electrodynamics of the wave propagation when the gas discharge is in contact with water. Depending on the wave power and the gas flow, it is possible to produce plasma at a low (room) temperature. The plasma is in nonequilibrium, with the electron temperature much higher than the gas/ liquid temperature. Because of this, many radicals and chemically active particles can be produced even at low temperatures. Depending on the operating conditions, this kind of discharge can have various applications in surface treatment, sterilization, and surface energy change, among others, including temperature-sensitive materials and liquids treatment.