Simulation of RF power and multi-cusp magnetic field requirement for H− ion sources

A computer simulation study for multi-cusp RF based H− ion source has been carried out using energy and particle balance equation for inductively coupled uniformly dense plasma considering sheath formation near the boundary wall of the plasma chamber for RF ion source used as high current injector for 1 Gev H− Linac project for SNS applications. The average reaction rates for different reactions responsible for H− ion production and destruction have been considered in the simulation model. The RF power requirement for the caesium free H- ion source for a maximum possible H− ion beam current has been derived by evaluating the required current and RF voltage fed to the coil antenna using transformer model for Inductively Coupled Plasma (ICP). Different parameters of RF based H− ion source like excited hydrogen molecular density, H− ion density, RF voltage and current of RF antenna have been calculated through simulations in the presence and absence of multicusp magnetic field to distinctly observe the effect of multicusp field. The RF power evaluated for different H− ion current values have been compared with the experimental reported results showing reasonably good agreement considering the fact that some RF power will be reflected from the plasma medium. The results obtained have helped in understanding the optimum field strength and field free regions suitable for volume emission based H− ion sources. The compact RF ion source exhibits nearly 6 times better efficiency compare to large diameter ion source.