Investigations of ION Beam Quality from a Pulsed Power Pinched Diode Using Particle-in-Cell Simulations

Abstract

A pinched-beam diode (PBD) consists of a thin annular cathode which emits electrons that are accelerated toward a planar anode. Once the energy deposited by the electrons on the anode is sufficiently large, a plasma forms on the anode and the electrons are strongly pinched toward the axis of the diode. An intense ion beam with current of 100’s of kA’s is also produced. This effort builds upon previously presented material and shows new particle-in-cell simulation results of a PBD where the focus is on the quality of the ion beams produced. The simulations provide additional detail to the formation of “hot spots” in the electron beam flow that produce regions of locally high charge and current density. As ions flow through the electron space charge cloud, the hot spots attract ions producing a non-uniform ion current distribution. The length of the cavity behind the cathode tip influences both the number and amplitude of the hot spots. Results will be presented to show that longer cavity lengths increase the number of hot spots but significantly reduces the amplitude producing smoother, more uniform ion beams than when the length of the cavity is short. Additional results will be presented that show the net current and ion bending angles are also significantly smaller when the length of the cavity is long.