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.