Simulation and experimental verification of radio frequency plasma discharge parameters in a MEOP system at the CSNS

Abstract Radio frequency (RF) plasma discharge constitutes a critical step in the generation of polarized 3 He by metastability exchange optical pumping (MEOP). In this study, a model of an inductively coupled plasma device is employed to investigate plasma parameters and enhance the design of coils and plasma characteristics using COMSOL simulations. The findings are compared with experimental results obtained from the MEOP system at the China Spallation Neutron Source (CSNS). The influence of inductive coil configuration and other parameters (gas pressure, RF power, and frequency) on plasma uniformity and distribution is systematically analyzed. Results indicate that as gas pressure, RF power, and frequency increase, the densities of electrons and metastable 3 He atoms also rise. Additionally, electronic temperature decreases with increasing gas pressure but exhibits minimal sensitivity to changes in power and frequency. A uniform weak plasma discharge was successfully generated, and the absorption from metastable 3 He atoms was measured with a weak probe laser and charge-coupled device camera, which enabled the determination of the metastable 3 He atom density. This research provides valuable insights for optimizing plasma discharge design and supports the establishment of the MEOP system at the CSNS.