Medium-Energy Particle Experiments - Ion Mass Analyzer (MEP-i)




  • Shoichiro Yokota (Osaka University)


  • Satoshi Kasahara (The University of Tokyo)


  • Kasahara, S., K. Asamura, Y. Saito, T. Takashima, M. Hirahara, and T. Mukai, Cusp type electrostatic analyzer for measurements of medium energy charged particles, Review of Scientific Instruments, 77, 123303, doi:10.1063/1.2405358, 2006.
  • Kasahara, S., T. Mitani, K. Ogasawara, T. Takashima, M. Hirahara, and K. Asamura, Application of single-sided silicon strip detector to energy and charge state measurements of medium energy ions in space, Nuclear Inst. and Methods in Physics Research, A, A 603, 355-360, doi:10.1016/j.nima.2009.02.004., 2009.
  • Yokota, S., S. Kasahara, T. Mitani, K. Asamura, M. Hirahara, T. Takashima, K. Yamamoto, and Y. Shibano, Medium-energy particle experiments--ion mass analyzer (MEP-i) onboard ERG (Arase), Earth, Planets and Space, 69(1), 172., doi:10.1186/s40623-017-0754-8., 2017.

Instrument Specifications

  • Energy range: <10 to 180 keV/q
  • Energy resolution: 7% (FWHM)
  • Energy steps: 16 steps per scan
  • Mass discrimination: H+, He++, He+, O+, O+2
  • Sensor field of view: 360° (azimuth) × 3.5° (elevation)
  • Number of anodes: 16
  • Geometric factor
    • 2.4×10-4 cm2 sr keV/keV/anode (normal)
    • 1.9×10-5 cm2 sr keV/keV/anode (narrow)
  • Time resolution: 4 s for full 3-D distribution function

Measurement Principle

The electrostatic analyzer measures the energy per charge and direction of incoming ions. The mass per charge is determined by time-of-flight (TOF) analysis. The charge is obtained by measuring the ion energy with solid state detectors (SSDs).

Other Information

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