An ion ring accelerator with plasma neutralization

The authors have undertaken simulations of neutralized ion ring accelerators in which the magnetic field is ramped by means of external field coils. A neutralized, slowly rotating ion ring is initialized in equilibrium with a weak axially directed magnetic field. Field coils are placed outside the ring, and mirror coils at the ends of the configuration. These coils are all given time-dependent currents in order to increase the magnetic flux threading the ion ring, and at the same time to increase the strength of the confining mirror fields. At the ring position, a strong azimuthal electric field is induced which serves to accelerate the ring to higher energy. Critical issues addressed in the simulations include the dynamics of the neutralizing electrons, which are followed explicitly. Previous simulations have indicated that the electrons may be subject to severe cyclotron heating, leaving the ions subject to disruption by their own space charge. Collective effects involving the interaction of the neutralizing electrons with the background neutral plasma may serve to alleviate this problem. Laboratory studies done at Cornell indicate that an ion ring neutralized by a gas fill does not fall victim to space charge disruption; the authors hope to demonstrate that a collisionless background also allows ring stability and acceleration