Coaxially driven microwave electrodeless UV lamp

The construction and operating characteristics of a microwave (MW) electrodeless UV lamp are described. Instead of using a MW oven or a MW cavity to excite a plasma discharge in a glass bulb, in this work the optical radiation emitted by the gaseous plasma discharge is produced by the near field of a coaxial cable dipole antenna placed inside the recess of the quartz bulb. Experimental results are reported, which were obtained by applying MW power up to 700 W in continuous wave regime to an Ar-Hg filled cylindrical bulb, and 160 W to a XeBr2 filled spherical bulb at 2.45 GHz. The UV emission from a 6 W Ar-Hg lamp is compared with a commercial lamp, demonstrating the advantages of the new method in terms of efficiency. When the lamp is excited at high MW levels, the MW coaxial antenna is cooled using forced air or water flowing into the glass recess. The physical modeling of the electromagnetic field distribution in the near-field region of the antenna and its interaction with the gaseous discharge are in good agreement with experimental results. The article focuses on the advantages of the non-cavity activation method of the UV lamp, taking into account industrial applications. In fact, the coaxial antenna excitation method is characterized by extreme simplicity, due to the absence of resonant metal enclosures. Thus, the ordinary MW cavity can be replaced by a number of independent MW UV emitters, placed inside a reaction vessel of arbitrary size and material.