Design of multi-layer grid in a giant electrostatic collection vessel of ultra-high sensitivity radon monitor

Abstract

Developing an ultra-high sensitivity electrostatic collection radon monitor benefits the scientific experiments of China Jinping Underground Laboratory. Here, a one cubic meter electrostatic collection vessel with a multi-layer hemispherical metal grid was designed to increase the collection efficiency of positively charged Po-218 ions. The 3D model of the giant electrostatic collection vessel was constructed using the COMSOL Multiphysics simulation software, and the potential and electric field distributions in the vessel were simulated. Numerical simulation results were obtained according to the different radii and voltages applied to the grid. The electric field between the vessel wall and grid, between two grids, and between the grid and surface of the PIPS detector must be set uniformly to reduce the collection time of the positively charged Po-218 ions. Simulation results showed that setting a charged metal grid in the vessel can optimize the electric field distribution, and setting a two-layer charged metal grid in the giant vessel can further increase the cost performance. The average collection times of the electrostatic collection vessel with the two-layer grid along the vertical and oblique lines approximately 15% and 13% of that without the grid. The rates of positively charged Po-218 ions that could pass through the one and two-layer metal grids were 86.78% and 50%. Optimizing the electric field can greatly increase the sensitivity of radon monitors and reduce the humidity restrictions.