Variable Density Scaling in the Global Model for Different Conductor Geometries of an RF Cathode

The global model for RF cathode performance is adapted to accommodate variable density effects due to diffusion. Different cathode geometries, including configurations with multiple rods located at an inner and outer radius (one with long conductors and one with short), are examined with this new framework. The ion saturation current of the variable-density model is generally higher than that of the previous no-diffusion model due to increases in plasma density. For a fixed surface area, long conductor configurations outperform short conductor ones and inner-mounted conductor configurations outperform outer-mounted conductor ones. The model is applied to experimental data and found to yield better fits than when diffusion is neglected. These results elucidate the importance of accounting for variable density within the RF cathode model and are discussed in context of improving RF cathode modeling and design.