Numerical investigation of the plasma-grid interaction of the LBL HIF source

Summary Form only given, as follows. HIF ion sources may require ion arcs confined behind wire meshes in order to provide sufficient ion optical stability with acceptable ion thermal spread. The physics of the plasma-grid interaction and implications for its use as a source for HIF accelerators has been investigated numerically. The authors have studied these interactions with two models: a time-evolutionary electrostatic (particle-in-cell) (PIC) code with an internal boundary configuration representing the grid wire(s) and a novel method for finding time-independent configurations with flow. The PIC algorithm easily and correctly describes the evolutionary behavior of any reasonable sort of initial plasma configuration subject to the applied voltages on the grid and the external extraction surface on the accelerator side. Coupled with the appropriate plasma evolution properties on the other side, the system is allowed to evolve to a self-consistent time-asymptotic configuration. The second approach, computing a time-independent state with flow, was motivated by the difficulty in finding the wire mesh size, spacing, and voltages which provide an acceptable brightness of the emerging ions. The second approach begins by postulating a desired ion flow without wraparound, so that no ions pass through a line of symmetry passing through each wire in the confining mesh. The problem then becomes one of finding the other parameters that are needed to provide this flow.<>