Simulation of Light Intensity of VUV Lamp Based on Inductively Coupled Plasma Discharge in Low-pressure Kr-He Mixture

The vacuum ultraviolet (VUV) light source derived from the Kr-He discharge is widely used for organic analysis, however the relevant model that greatly facilitates the design of high-performance VUV light sources remains to be developed. This study explores a model for simulating the light intensity of the VUV lamps based on the inductively coupled plasma (ICP) discharge in the low-pressure Kr-He mixture. Two typical ICP based light sources, i.e., a 13.56 MHz VUV lamp with an external coil and a 2.65 MHz VUV lamp with an internal coil, were successfully simulated with the COMSOL Multiphysics software coupled with a fluid model. The rate coefficients of the main reactions involved in the production of VUV radiations from Kr-He plasma were summarized and input in the model. The concentrations of Kr * ( 3 P 1 ) and Kr * ( 1 P 1 ), which are main VUV-generation species, were set as output to evaluate the overall light intensity of the VUV lamp. As a result, the optimal designing parameters (the length and density of the coil and the radius of the lamp) as well as operating parameters (the input power, the pressure inside the lamp, and the mixing ratio of Kr to He) were obtained for the maximum light intensity. The reliability of the model was further verified by comparing the measured photon flux with the simulated concentrations of Kr * ( 3 P 1 ) and Kr * ( 1 P 1 ) as functions of the pressure and mixing ratio of Kr-He mixture, which showed good agreements in variation tends. The model provides a great convenience for the development of ICP based VUV lamp with high light intensity and stability.