Charged particle motion inside the retarding potential analyzer

One of the Ionospheric Plasma and Electrodynamics Instrument (IPEI) payload onboard the Republic of China satellite 1 (ROCSAT-1) spacecraft is a Retar ding Potential Analyzer (RPA) to measure the ionospheric plasma composition , temperature, and the ram velocity of the flow. A three-dimensional comput er model has been developed to simulate the ion and electron motions inside the RPA of the IPEI payload. The dynamical changes in the charged particle s' motions corresponding to different electric potential profiles inside th e RPA detector resulted in some distinctive measuring characteristics of th e RPA detector, which show discrepancies in the measured of currents at the collector plate between the analytical model and the computer simulation. The important discoveries in the computer model are: (a) Ion transparency c annot be represented by the physical grid sizes in the detector. The alignm ents of the grid wires will also affect the ion transparency. The grid plan es should be aligned for the maximum optical transparency to detect light i on fluxes. (b) Cut-off energy for protons is not as sharp as indicated in t he analytical model. The contamination in the collector current from lighte r ion species is possible. (c) Electron contamination at the collector plat e is noticed if the mesh sizes are larger than the electron Debye length. ( C) 2000 American Institute of Physics. [S1070-664X(99)04212-3].