Development of Medium Energy Ion Mass Spectrometer for Future Missions in the Inner Magnetosphere of the Earth

Details Development of Medium Energy Ion Mass Spectrometer for Future Missions in the Inner Magnetosphere of the Earth Development of Medium Energy Ion Mass Spectrometer for Future Missions in the Inner Magnetosphere of the Earth

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm33c0462k&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SM33C-0462

Physics

Space Physics

2730 Magnetosphere: Inner, 2778 Ring Current, 2788 Magnetic Storms And Substorms (7954), 2794 Instruments And Techniques

Scientific paper

It is well known that intense fluxes of energetic particles are seen in the inner magnetosphere of the Earth during magnetic storms and substorms; ring current ions and radiation belt electrons with energies of several hundred keV up to more than a few MeV are generated and/or transported. However, their acceleration mechanisms and sources have not been well understood, partly due to insufficient data of medium-energy ions (from several 10 to ~200keV/q). This is one of the most important problems in magnetospheric physics, and in general, space physics. The key information for this study is the energy (E) distribution, charge state (q) and mass (m) of particles. We also recognize the importance of detailed information on three-dimensional distribution functions in this energy range; it is required from a viewpoint of the influence of plasma waves on the evolution of the storm time ring current. We have started to develop a Medium energy Ion Mass Spectrometer (MIMS), which can measure energy (E), mass (m), and charge state (q) of each ion in the medium-energy range. The instrument consists of 1) an energy-per-charge (E/q) ElectroStatic Analyser (ESA), 2) a Time-Of-Flight (TOF) unit that provides velocity (v) of particles, and 3) Solid-State Detectors (SSD), which measure the total energy (E). To detect an ion, we use three signals; a start signal and a stop signal in TOF unit provide us ion velocity, and a signal from SSD tells us the incident ion energy. A triple coincidence technique with these three signals is also useful for discrimination of true particle signals from background noise. Thus the instrument can provide E/q, v and E, from which the charge state (q) and mass (m) can be deduced unambiguously. The techniques of ESA, TOF, and SSD are conventional for lower or higher energy range, but the application to medium energy range is not trivial. One of the most serious problems is a size of the instrument. The size of ESA becomes too large, if we take conventional top-hat type ESAs; it is because we have to keep restrictions of high voltages applied to sensor electrodes. Therefore, we newly invented cusp type ESA. Its novel idea_@makes a size of medium energy ESA much smaller and keeps full pitch angle coverage (by using spacecraft spin). We_fve done many computer simulations about cusp type ESA and completed the design in detail, for observations in the inner magnetosphere. The calculation shows the highest sensitivity (total g-factor: 2.2x10-2[cm2 sr keV/keV]) ever, compared to past electrostatic analysers in medium energy range. We also simulated TOF unit, which follows ESA. We use only one MCP for detection of start-electron and stop-electron; the idea reduces weight and cost of the sensor. We have fabricated the proto-model (currently only ESA) and tested its performance. We will make a presentation on the results of computer simulations about ESA and TOF unit. In addition, we will show the results of some experiments with ESA and discuss analyser properties.

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