QUICKSILVER simulations of applied-B extraction diodes

Recent simulations of the barrel diode configuration with the 3-D particle-in-cell code QUICKSILVER have detailed a rich evolution of unstable electromagnetic waves [Phys. Rev. Lett. 67, 3904 (1991)]. Preliminary simulations of applied-B extraction diodes with the 3-D particle-in-cell code QUICKSILVER suggest some significant differences in equilibrium and stability properties between extraction and barrel diodes. The extraction diode simulations suggest better divergence and, when a limiter is employed to reduce divergence, potentially better efficiency. In the case of proton beam simulations, the low frequency ion mode was not found even for peak ion current enhancements in excess of 10. The ion mode was exhibited by the lithium beam extraction diode simulations. Limiter simulations with both proton and lithium beams demonstrated very good divergence. A scheme for obtaining uniform ion current density profiles based on a uniform dynamic gap calculation appears promising.