ERG/MGF The magnetic field measurement in the inner magnetosphere Ayako Matsuoka(ISAS/JAXA), Yoshizumi Miyoshi(Nagoya Univ. STE Lab.), Manabu Shinohara(Kagoshima National College of Technology), Yoshimasa Tanaka(NIPR), Tsutomu Nagatsuma (NICT), Kazuo Shiokawa(Nagoya Univ. STE Lab.), Masahito Nose(Kyoto Univ.), Mariko Teramoto (ISAS/JAXA) Reiko Nomura (ISAS/JAXA) 2014/4/27 Science Objectives Related to Magnetic Field Experiment Mechanism Working on the Acceleration of Relativistic Electrons External source process via adiabatic acceleration The energy of electrons increases due to the conservation of their first and second adiabatic invariants Key Observations: Global Magnetic Field Structure MHD waves causing radial diffusion (e.g. Pc5, 150∼600 seconds period) Internal acceleration process Resonant interactions by whistler-mode waves cause relativistic electron acceleration inside the radiation belts Key Observations: Anisotropic distribution of hot electrons generating whistler waves 2 2014/4/27 Science Objectives Related to Magnetic Field Experiment Electron Flux Loss Process To understand the dynamics of the radiation belt, the electron flux loss process, as well as the enhancement process, should be studied. Pitch angle scattering by electromagnetic ion cyclotron (EMIC) waves is considered to cause precipitation of relativistic electrons in the atmosphere Key observations : EMIC waves (several∼100Hz frequency) [Usanova et al., 2008] ground and THEMIS observations 4 Mission objectives of ERG MGF I. Strength and direction of the ambient magnetic field • Study of the global structure and topological modification of the field line • Measurement of the magnetic field strength to derive the cyclotron frequency • Measurement of the direction of the ambient field to study the anisotropic distribution of plasma, propagation direction of waves • Study of the electric current in the inner magnetosphere II. MHD (Pc5 ULF) waves • Transport of charged particles across the magnetic field, quantitative evaluation of the contribution to the external supply process. III. EMIC waves • Study of the loss of the high-energy particles by the pitch-angle scattering Magnetometer for ERG (MGF) Electronics Sensor 5m MGF characteristics Flux-gate magnetometer Heritages : Sakigake, Akebono, GEOTAIL, Nozomi, Kaguya, BepiColombo MMO Dynamic range (nT) ±60000 / ±8000 Resolution (pT) 114/ 15 Original sampling freq. (Hz) 256 Frequency range Cut-off frequency (Hz) ~ 120 Accuracy (room temperature) Sensitivity (%) < 0.05 Alignment (deg) < 0.5 Sensor (g) 120 Electronics (g) 2780 Cable (g) 298 Sensor (mm) 40 x 40 x 80 Electronics 260x120.5x165.8 (W) 1.91 Max (excluding CPU and PSU) Data sampling Weight Dimension Power consumption 2014/4/27 8 Required Absolute Angular Accuracy • MGF is required to measure the magnetic field direction with 1 degree accuracy at L < 4.5 Re. Eastward Ring Current R1 Current Ring Current Magnetic Dipolarization Fine Structure in The Ring Current R2 Current Small Magnetic Perturbations Do not need absolute accuracy MGF Design Because the radiation environment is very severe, MGF for ERG needs to have radiation tolerance. It is designed based on BepiColombo MMO MGF-I. Modifications are made in : • Space Wire clock frequency • Command and telemetry data • Range control • Feedback parameters 2014/4/27 MGF block diagram Sensor and Driver Sensing Electronics Delta-Sigma ADC Space-Wire Interface Points different from BepiColombo MMO MGF-I are represented by red 10 Delta-Sigma analog to digital converter One of the subjects to design the high-performance fluxgate magnetometer is the analog to digital conversion. The resolution of the commercial ADC parts for the space use is insufficient to achieve both the wide-range and precise measurements. It becomes significantly severer when high radiation tolerance is required (BepiColombo, ERG). We have developed a discrete circuit of delta-sigma ADC which is built by radhard parts. The resolution is 20 bits (4pT) for BepiColombo MMO MGF-I, and 18 bits (61pT) for ERG MGF. Delta-sigma ADC block diagram MGF BBM CPU BBM 2014/4/27 Noise level of BBM EMIC Observation by AMPTE Environment noise ±80000nT Range 88 pT/rootHz 8.3pT/rootHz @1Hz EMIC Observation by CRESS L=3∼8 265 pT/rootHz 13 2014/4/27 15 EMC (Magnetic cleanliness) requirement Magnetic noise generated by the spacecraft degrades the quality of the magnetic measurement. For the accurate magnetic field measurement, the magnetic cleanliness of the spacecraft is very important. In the ERG project, the magnetic cleanliness of each component is required to satisfy the followings. Magnetic field strength at 1 m sphere around each sub-component: <50nT Variation of the magnetic field (0.1-20Hz) at 0.5m distance: <10nT Variation of the magnetic field (0.1-60Hz) at 0.5m distance: <30nT ISAS Magnetic Shielding Chamber (three spherical layers, inside diameter = 5m) EMC Experiment in the Shielding Chamber Summary • Magnetic field experiment is the key of the ERG mission to explore the radiation belt. Its main role is to measure the global magnetic structure, Pc5 ULF waves, and EMIC waves, so on. • For ERG, a set of fluxgate magnetometer (MGF) is designed based on BepiColombo MMO MGF-I to have the required radiation tolerance. • The characteristics of MGF is defined to meet the requirement from the ERG mission objectives. • EMC (magnetic cleanliness) program is carried out to reduce the magnetic interference from the spacecraft.
© Copyright 2021 ExpyDoc