Particle-in-Cell Simulations of Ion Beam Properties Produced From a Planar Pinched-Beam Diode

Particle-in-cell simulations of a 1.6-MV, 400-kA, and 50-ns planar pinched-beam diode show that ion current and efficiency increase as anodes are made longer and thinner. At the length limit of this investigation, we observe efficiencies reaching 75% with approximately 300 kA of ion current. In general, making anodes longer and thicker improves uniformity but reduces fluence. However, there is a limit to uniformity improvement as thicker anodes display spotty ion emission behavior. Thinner anodes can generate higher fluences than thicker anodes for a portion of the anode length due to electron reflexing. However, uniformity is not improved and the fluence drops substantially in a portion of the anode due to virtual cathode expansion in the diode. Among all simulations, the best balance of fluence and uniformity was for an 8-cm-long, 400-
$\mu \text {m}$
-thick anode, which provided a fluence of 10 cal/cm2 over 100 cm2 with a uniformity of ±25%. Thinner anodes also show a broader ion energy distribution than thicker anodes, likely due to ions coupling to an oscillating electric field associated with an instability in the diode particle flow.