Simulation study of applied-B ion diodes with plasma prefill

Summary form only given. The prefilling of an ion diode with plasma can establish an electron distribution in the diode that allows ion flow well above the Child-Langmuir limit in a very short time compared to the pulse length. The relativistic, electromagnetic, 2.5-D PIC (particle-in-cell) code MAGIC has been used to examine this process in detail with a realistic diode configuration to help quantitatively define plasma-filled ion diode experiments. Simulations demonstrate that there is a prefill density regime for which the diode can operate nearly instantaneously on the saturated characteristic. With the right prefill the saturated electron density profile can be an initial condition. An informative figure of merit is the beam impedance: the ratio of the diode voltage to the ion beam current. For the V_c=15 MV Li example without plasma prefill, the beam impedance drops steadily (from 120 Ω) until the diode voltage reaches about 8 MV; with plasma prefill the beam impedance is nearly constant (about 10 Ω) with diode voltage above 1 MV