Low-Energy Ion Transport Between Two Insulating Parallel Plates

Experimental data are presented for low-energy singly charged ion transport between two insulating parallel plates. Using a beam intensity of approximately 20 pA, measurements of the incoming and transmitted beams provide quantitative temporal information about the charge deposited on the plates and the guiding probability. Using a smaller beam intensity (~1 pA) plate charging and discharging properties were studied as a function of time. These data imply that both the charge deposition and decay along the surface and through the bulk need to be modeled as acting independently rather than as a combined weighted average. A further reduction of beam intensity to ~25 fA allowed temporal imaging studies of the positions and intensities of the guided beam plus two bypass beams to be performed. Because of the parallel plate geometry, SIMION software was used to simulate trajectories of the guided and bypass beams. This provides information about the amount and location of deposited charge and, as a function of charge patch voltage, the probability of beam guiding and how much the bypass beams are deflected. Information about the electric fields which provides insights into the relative charge decay via the surface and bulk is also obtained. An equivalent electric circuit model of the parallel plates is used to associate the deposited charge with the patch voltage. To achieve internal consistency between the various sets of experimental data and the SIMION information, the deposited charge is implied to be distributed primarily on the inner surface of the plates, transverse to the beam direction, rather than being distributed throughout the entire plate.