The use of UV-radiation from mercury plasmas is a common method for water disinfection. However, because of the toxicity of the mercury, the filling amount should be lowered or the mercury should be replaced [1]. Therefore, we developed medium pressure and inductively driven plasma lamps for UV generation, in an EU founded “Horizon2020” project.
Since field effect transistors made of wide bandgap semiconductor materials like SiC and GaN are available, it is possible to build highly efficient inverters for powers ≥1 kW and frequency range up to 3 MHz [2]. Those frequencies can be used for an efficient operation of inductive plasmas [3]. Because in the inductive operation no electrodes are needed, it is possible to use lamp-filling materials, which would react in common lamps with the electrodes. The electrodeless operation opens the possibility to use a wide range of fillings to replace the mercury. Furthermore, in conventional lamps the electrodes are the most limiting factor for the lifetime of the lamps.
In our work, we tested different lamp-fillings. Due to the required vapour pressures halides are preferred here. Furthermore, with regard to the heat distribution, radiation surface and the RF power coupling, the geometry of the lamp vessels were optimized. Therefore different dimensions were tested and the influences were monitored by temperature, current and radiation measurements.
In addition, different coil geometries were simulated and tested to optimize the compromise between the radiation reducing coil shading and the needed field strength at a given current for the inductive operation.
With our lamps, we reach efficiencies nearly in the range of standard medium pressure electrode lamps. The lifetime of electrodeless operation should be drastically higher. Therefore, the presented inductively driven UV-sources could provide a good alternative to conventional technologies.
References :
[1] Regulation (EU) 2017/852 of the European Parliament and of the Council of 17 May 2017 on mercury, and repealing Regulation (EC) No 1102/2008
[2] Denk et. Al. R DS(on) vs. Inductance Comparison of SiC MOSFETs in 7pin D2Pak and 4pin TO-247 and their benefits for high-power MHz. IET Power Electronics 2019
[3] Popov, O.A. Efficient Light Source Based on an Inductive Ferrite-Free Discharge at Frequencies of 300-3000kHz. Technical Physics 2007, 52, 751–758
