A new digital ion drift meter for thermal plasma measurement

Summary form only given. The Digital Ion Drift Meter (DIDM) is being developed as a replacement for analog spacecraft drift-meters. It combines the single-ion counting capability of a Micro-Channel Plate (MCP) with a position-determining anode. Careful electrostatic design is needed to create an instrument that can simultaneously measure bulk and differential plasma properties at very low densities. A simple pinhole to image ions straight onto an MCP would be light-sensitive. Instead, the DIDM design turns ions around and accelerates them using the MCP´s surface voltage. The imaging effect of the aperture is preserved by careful CAD modeling of the detector´s geometry. Performance has been optimized by simulating the trajectories of ions entering the device. Computer programs are used to simulate trajectories over a comprehensive velocity spectrum. The models are evolved into manufacturing specifications and verified in a calibration facility. Comparisons between models and prototype performance are good. This approach speeds the design cycle and provides a capability to investigate effects beyond the reach of practical lab techniques, such as very-low-energy particles and finite-aperture effects.