The voltage dependent transmission function of a retarding field analyzer

Retarding field analyzers (RFA) are widely used to measure ion energy distributions and fluxes from plasmas, but quantitative flux determination requires accurate knowledge of their grid stack transmission. The dependence of the transmission factor on the barrier voltage is investigated through a combination of experimental measurements and ion trajectory simulations. Experimental results for different ion species reveal a common transmission-voltage relationship independent of ion species, indicating that the effect is intrinsic to the analyzer. Ion trajectories through a four-grid RFA were modeled using SIMION to examine the influence of grid alignment and bias configuration. Without retarding potential, the transmission can be estimated by optical inspection. However, applied voltages introduce electrostatic lensing, which is most pronounced when grids are geometrically aligned. The electron suppressor grid introduces appreciable oscillations in transmission as a function of the voltage just below the ion cutoff voltage. The overall transmission arises from an intricate interplay of lensing, alignment, and grid spacing.