Investigations of Ion Beam Quality from a Planar Pulsed Power Pinched-Beam Diode

A pinched-beam diode consists of a cathode plate that emits electrons that are accelerated toward an anode plate. Plasma forms once the electrons deposit enough energy into the anode. This enables the electrons to propagate to the end of the anode, producing intense ion beams on either side of the anode. This paper builds on previously presented material. [1] It shows particle-in-cell simulation results of a planar ion diode. [2] The rod-pinch diode, which creates X-rays, is the inspiration. [3] Instead of a rod, the anode is a flat planar plate. While ion current is a parasitic loss for radiographic applications, this work focuses on enhancing ion production and evaluating ion beam quality. Results show 40-75% ion efficiencies depending on anode length and thickness. Making anodes longer and thicker improves uniformity but reduces fluence. However, there is a limit to uniformity improvement as thicker anodes develop 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 in a portion of the anode due to virtual cathode expansion. Thinner anodes also show broader ion energy distributions than thicker anodes, likely due to ions coupling to an oscillating electric field associated with an instability in the particle flow.