Science topics and ERG /MGF

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
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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
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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
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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
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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.

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