10:45 〜 12:15
[PEM09-P17] 静止軌道高エネルギー陽子線計測装置(CHARMS-p)の開発状況(II)
キーワード：宇宙天気、高エネルギー陽子、シリコン半導体検出器、チェレンコフ光検出器
National Institute of Information and Communications Technology is developing a space environment measurement instrument (CHARMS: charging and radiation monitors for space weather) that can be mounted on the next generation meteorological observation satellite, based on the research project "Research and Development of observing technology on Himawari satellite" commissioned by the Ministry of Internal Affairs and Communications. As research and development related to space radiation monitoring technology, we are conducting research and development for measuring the energy of proton flux with wide energy range. The energy range covered by the proton flux measurement instrument (CHARMS-p) ranges from 10 MeV to over 1 GeV, thus the dynamic range of the proton flux extends to six orders of magnitude. Therefore, the proton flux measuring instrument is divided into a low energy side (CHARMS-p-lo) and a high energy side (CHARMS-p-hi) having different G factors, respectively.
The energy range of protons measured by CHARMS-p-lo is from 10 to about 500 MeV, and the energy of incident protons is measured by stacked silicon semiconductor detectors (SSDs). CHARMS-p-lo has eight layers SSDs, consisting of one SSD with a diameter of 12 mm and a thickness of 80 um and seven SSDs with a diameter of 32 mm and a thickness of 1500 um, both manufactured by Micron Semiconductor. Protons up to about 50 MeV stop in the stacked SSDs, and protons with higher energies penetrate the SSDs. When the incident energy of protons further increases (>500 MeV), the SSDs loses its energy sensitivity to protons, making it impossible to apply the measurement method using the SSD. In particle irradiation calculations using Geant4 software, we confirmed that the stacked SSDs section can measure energies from 10 MeV to 500 MeV, and that a housing shield of 3.5 mm can shield particles that are not the target of energy measurement.
In CHARMS-p-hi, the high-energy side proton flux measurement instrument of CHARMS-p, Cherenkov light is used as the energy measurement mechanism. Cherenkov light is the light emitted when a charged particle passing through a medium (Cherenkov radiator) moves beyond the speed of light, which is determined by the refractive index of the radiator. The number of photons generated is related to the velocity of the particle. Therefore, the refractive index of the Cherenkov radiator determines the minimum energy (critical energy) of the protons from which the Cherenkov light is generated. On the other hand, a particle with energy above a certain level approaches the speed of light (in a vacuum) and the generated Cherenkov photons become saturated. As for the Cherenkov radiator, synthetic quartz was selected from several candidates because of its radiation resistance, good transmittance for short-wavelength light, and suitability for measuring the energy near 1 GeV. To measure the energy of up to few GeV protons by Cherenkov radiation, we installed a prototype proton flux measurement instrument at the J-PARC Center of the Japan Atomic Energy Agency and conducted proton beam irradiation tests at the energies of 400 MeV, 800 MeV, 1 GeV, 2.2 GeV, and 3 GeV. As a result, it was confirmed that it is possible to measure the energy between 800 MeV and 3 GeV using synthetic quartz (refractive index 1.48) as the Cherenkov radiation source. In addition, a vibration resistant PMT made by Hamamatsu Photonics is used for detecting Cherenkov light, so that the structure can withstand vibration and shock at the time of launching to a geostationary orbit. The Cherenkov photodetector is surrounded by a plastic scintillator to provide an anti-coincidence function against particles entering from outside the field of view. Based on these results, the equipment design will be carried out and the basic design of the engineering model will be completed.
The energy range of protons measured by CHARMS-p-lo is from 10 to about 500 MeV, and the energy of incident protons is measured by stacked silicon semiconductor detectors (SSDs). CHARMS-p-lo has eight layers SSDs, consisting of one SSD with a diameter of 12 mm and a thickness of 80 um and seven SSDs with a diameter of 32 mm and a thickness of 1500 um, both manufactured by Micron Semiconductor. Protons up to about 50 MeV stop in the stacked SSDs, and protons with higher energies penetrate the SSDs. When the incident energy of protons further increases (>500 MeV), the SSDs loses its energy sensitivity to protons, making it impossible to apply the measurement method using the SSD. In particle irradiation calculations using Geant4 software, we confirmed that the stacked SSDs section can measure energies from 10 MeV to 500 MeV, and that a housing shield of 3.5 mm can shield particles that are not the target of energy measurement.
In CHARMS-p-hi, the high-energy side proton flux measurement instrument of CHARMS-p, Cherenkov light is used as the energy measurement mechanism. Cherenkov light is the light emitted when a charged particle passing through a medium (Cherenkov radiator) moves beyond the speed of light, which is determined by the refractive index of the radiator. The number of photons generated is related to the velocity of the particle. Therefore, the refractive index of the Cherenkov radiator determines the minimum energy (critical energy) of the protons from which the Cherenkov light is generated. On the other hand, a particle with energy above a certain level approaches the speed of light (in a vacuum) and the generated Cherenkov photons become saturated. As for the Cherenkov radiator, synthetic quartz was selected from several candidates because of its radiation resistance, good transmittance for short-wavelength light, and suitability for measuring the energy near 1 GeV. To measure the energy of up to few GeV protons by Cherenkov radiation, we installed a prototype proton flux measurement instrument at the J-PARC Center of the Japan Atomic Energy Agency and conducted proton beam irradiation tests at the energies of 400 MeV, 800 MeV, 1 GeV, 2.2 GeV, and 3 GeV. As a result, it was confirmed that it is possible to measure the energy between 800 MeV and 3 GeV using synthetic quartz (refractive index 1.48) as the Cherenkov radiation source. In addition, a vibration resistant PMT made by Hamamatsu Photonics is used for detecting Cherenkov light, so that the structure can withstand vibration and shock at the time of launching to a geostationary orbit. The Cherenkov photodetector is surrounded by a plastic scintillator to provide an anti-coincidence function against particles entering from outside the field of view. Based on these results, the equipment design will be carried out and the basic design of the engineering model will be completed.