Conservation of axial momentum in intense ion beam systems

Abstract

In a number of systems, interaction between electrons and ions results in acceleration of ions. Because of the large ion/electron mass ratio, the efficiency of intense ion beam sources can often be low. A macroscopic momentum conservation law is presented which allows the efficiency of collective accelerators and ion diodes to be evaluated. The application of the equation is straightforward and does not depend on the specific dynamical processes involved. A number of new relations are derived from the basic equation including the efficiency of a collective accelerator, the average ion velocity for collective acceleration in vacuum, the ratio of electron and ion currents in a pinched beam diode, and a relation for current enhancements in magnetically insulated diodes. These relations also serve to elucidate the role of magnetic pressure in intense ion beam systems.