Numerical simulation of strong proton rings

Recent calculations suggest the possibility of achieving a Lawson breakeven condition by the magnetic compression of proton rings to field reversal. This report describes a physical model and computer code RING developed to study equilibria of strong proton rings and their behavior under an adiabatic increase in the external magnetic field. Ring ion motion is followed using a volume-weighted finite-size particle-in-cell method. Because of the very short electron time scale, the electrons are simulated by a simple fluid model using Ohm's law. Quasineutrality, current neutralization in the r-z plane, cylindrical symmetry and a magneto-static model are assumed. Preliminary results indicate that (a) equilibria tend to be intermediate between the long layer and bicycle tire cases; and (b) compression past field reversal on the axis is possible within the framework of this model.