Magnetic Field Experiment (MGF)

A fluxgate magnetometer has been adopted for MGF to measure ambient magnetic fields, ULF Pc5 pulsations, and Pc1/EMIC waves in the inner magnetosphere. Since distortion of ambient magnetic fields produced by the ring current affects the particle distribution and trajectories in the inner magnetosphere, accurate measurement of the magnetic field deviation from the intrinsic magnetic field is important to evaluate the effect and evolution of the ring current.

MGF is designed to obtain the magnetic field deviation with an accuracy of better than 3° during space storms. As summarized in Table 1, MGF has two dynamic ranges of ±8000 and ±60000 nT. The measurement resolution is 19 bits, so that the respective accuracies are 31 and 250 pT for the two dynamic ranges. The frequency range obtained by MGF is from DC to several tens of Hz. (Since the sampling frequency is 256 Hz, the cut-off frequency is ~120 Hz.) This frequency range covers the local ion cyclotron frequency, which is key to the understanding of the interaction between MHD waves and ambient plasma. EMIC waves may be observed by MGF as well as PWE (see Figure 1).

The design of MGF onboard ERG  is based on that of MGF-I onboard BepiColombo MMO [Baumjohann et al., 2010; Matsuoka et al., 2012]. The sensor of MGF is mounted at the tip of the 5 m boom deployed from the spacecraft to reduce noise in measurement data.

Figure 1: Frequency range of the plasma wave experiment and magnetic field experiment instruments.

Table 1: Specifications of MGF (1)
Sampling Frequency256 Hz
Dynamic Range±8000 nT (L>2), ±60000 nT (L<2)
Magnetic Field Resolution31 pT (L>2), 250 pT (L<2) (19 bits)
Angle Accuracy< 1°

Table 2: Specifications of MGF (2)
Size (mm)Weight (kg)Power (W)
Electronics150 x 165 x 501.352
Sensor40 x 40 x 800.15
Extensible Mast288 x φ270 (withdrawn)
5318 x φ270 (extended)

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