High Z Droplets-A Novel Source of Heavy Ions for Nuclear Physics

Substantially higher beam currents and luminosities must be achieved to continue fundamental advances in experimental nuclear physics and astrophysics research. Present heavy ion beam injectors, based on electron cyclotron resonance (ECR) techniques, must be optimized to produce the necessary beam current with sufficient reliability and reasonable cost. This project will develop a novel, fully-kinetic simulation code to investigate the loading of heavy metals into ECR ion sources (ECRIS) via such alternate mechanisms as vapor loading, ion sputtering, and laser ablation. In Phase I, a massively-parallel 3D particle-in-cell (PIC) code was enhanced by adding impact ionization and recombination models. The simulation generated oxygen ionization state distributions consistent with published experimental data. The feasibility of using a particle-in-cell (PIC) code to model important kinetic effects in an ECRIS plasma was demonstrated. In Phase II, coordinated simulations and experiments will be used to optimize the location and orientation within the ECR magnetic bottle for both a metal vapor oven and a biased rod for ion sputtering. The merit criteria will be ion current at the extraction aperture, overall ionization efficiency, and the number of vapor particles lost to the wall. ECR loading via laser ablation will be simulated. The PIC simulation code will be further enhanced with ion/neutral charge exchange models, as well as with parametric models for the three types of neutral injection sources. The plasma shape and ion distribution functions at the extraction aperture will be modeled, providing improved initial conditions for extraction optics simulation codes. Commercial Applications and other Benefits as described by the awardee: A high-quality, commercial modeling tool for ECR sources, which is benchmarked against experimental results, should provide a detailed understanding of the loading process of ECR sources, increasing the ion beam production efficiency of rare and expensive isotopes.