Investigation of Water-Vapor Plasma Excited by Microwaves as Ultraviolet Light Source

• Published in: IEEE transactions on plasma science 2009-01, Vol.37 (1), p.107-112
• Main Authors: Oh, J.-S., Kawamura, K., Pramanik, B.K., Hatta, A.
• Format: Article
• Language: English
• Subjects: Absolute spectrum calibration; Density; Density measurement; Electric discharges; Electron tubes; Exact sciences and technology; Excitation; Gas tubes (electronic); Hydrogen; Irradiation; Lamps; Laser-plasma interactions; Light sources; Mercury lamps; microwave; Microwave measurements; Microwaves; OH radical; Optical (ultraviolet, visible, infrared) measurements; Optical saturation; optical-emission spectroscopy (OES); Other gas discharges; Oxygen; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma; Plasma diagnostic techniques and instrumentation; Plasma sources; Power measurement; Pressure measurement; rotational temperature; saturated water-vapor pressure; Ultraviolet; ultraviolet (UV); Ultraviolet radiation; Water; water-vapor discharge; X-ray, gamma-ray and particle generation
• ISSN: 0093-3813; 1939-9375
• DOI: 10.1109/TPS.2008.2007732

The potential of using water-vapor plasmas excited by microwaves as a ultraviolet (UV) light source has been investigated by using various pressures and input powers. The UV irradiation power increased and saturated at a pressure range dependent on the input power. On the other hand, other visible and infrared emissions corresponding to four atomic lines, i.e., the Balmer series of hydrogen at 486.1 nm ( Hbeta) and 656.3 nm (Halpha) and oxygen atoms at 777.2 and 844.6 nm, were clearly decreased with an increase in the total gas pressure. It was found that pressures (1.4-2.0 kPa) near the saturated water-vapor pressure were found to give the most intense UV irradiation. With a vapor pressure of 1.6 kPa and a total microwave power of 300 W, the power density of UV (Gamma uv ) was measured to be 10.5 muWmiddotcm -2 at a distance of 30 cm from the center of the discharge tube as measured through an optical viewing port on the cavity discharge applicator. This value for (Gamma uv ) is comparable to that for a mercury lamp. However, the (eta uv ) efficiency was estimated to be considerably lower than that of a mercury lamp.