Plasma Wave Experiment (PWE)

PWE measures electric fields in a frequency range from DC to 10 MHz and magnetic fields in a frequency range from a few Hz to 100 kHz. It is based on the design slightly modified from the plasma wave investigation (PWI) onboard the BepiColombo Mercury Magnetospheric Orbiter (MMO) [Kasaba et al., 2010]. The electric field component is measured with two pairs of wire dipole antennas with ~32 m tip-to-tip length. The magnetic field component is measured with three-axial search coils. They are served by two receivers, EWO (electric field detector (EFD), wave form capture (WFC), and onboard frequency analyzer (OFA)), and high frequency analyzer (HFA). EWO always obtains electric and magnetic field data as low-frequency waveforms (512 Hz sampling), wave spectra (10 Hz to 20 kHz), and their spectral matrices, which can be used to determine wave normal angles and Poynting fluxes. The spacecraft potential (256 Hz sampling) is also measured to derive rapid variations of the electron density. Furthermore, EWO stores raw waveforms of the electric and magnetic fields (60 kHz sampling), which are partially downloaded to the ground within the telemetry limit after the selection by researchers checking low-resolution data. HFA obtains wave spectra of the electric field (10 kHz to 10 MHz) and the magnetic field (10-100 kHz). The electron density is identified on board from the upper-hybrid resonance frequency. Electric and magnetic waveforms from EWO and the electron density from HFA will be provided to S-WPIA to identify wave modes and the characteristics of wave-particle interactions.

Figure 1 shows the frequency ranges of PWE and MGF, together with key plasma waves expected at the ERG  orbit. Whistler mode chorus waves [e.g., Santolik et al., 2003; Miyoshi et al., 2007; Omura et al., 2008; Li et al., 2011] and magnetosonic mode waves [e.g., Kokubun et al., 1991; Kasahara et al., 1994; Meredith et al., 2008] are important for understanding nonadiabatic acceleration generating relativistic electrons. EMIC waves [e.g., Sawada et al., 1991; Kasahara et al., 1992; Jordanova et al., 2008] excited by ring current ions cause rapid pitch angle scattering of relativistic electrons [e.g., Summers and Thorne, 2003; Albert, 2003; Miyoshi et al., 2008]. In the plasmasphere, whistler mode hiss waves work for pitch angle scattering of high-energy electrons [e.g., Lyons et al., 1972; Meredith et al., 2009].

PWE measurements will also reveal how the electric field in the inner magnetosphere evolves during space storms. Convective electric field causes global-scale transport of plasma sheet and ring current populations. It includes large electric fields as observed in the inner magnetosphere by CRRES and Akebono [e.g., Rowland and Wygant, 1998; Nishimura et al., 2007], localized electric fields associated with subauroral polarization streams affecting the evolution of the plasmasphere [e.g., Goldstein et al., 2003], and electric fields in the inner magnetosphere largely controlled by the magnetosphere-ionosphere coupling via the region-2 current system [e.g., Ebihara et al., 2004]. Furthermore, combining with MGF, PWE can detect ULF Pc5 pulsations with ~5 min period, which drive quasi-adiabatic acceleration by radial diffusion.

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

Table 1: Minimum Telemetry Plan
Instrument NameTypeTime ResolutionBitFrequency PointsChannels
EWO-EFD (DPB)spectrum (2-80 Hz)1 Hz8402
EWO-EFD (DPB)waveform8 Hz16-2
EWO-EFD (SPB)waveform4 Hz16-4
EWO-OFA/WFC (E)spectrum (10 Hz - 20 kHz)2 Hz8661
EWO-OFA/WFC (E)waveform (ELF)1024 Hz14 (16)-2
EWO-OFA/WFC (E)waveform (VLF)65536 Hz14 (16)-2
EWO-OFA/WFC (B)spectrum (10 Hz - 20 kHz)2 Hz8661
EWO-OFA/WFC (B)waveform (ELF)1024 Hz14 (16)-3
EWO-OFA/WFC (B)waveform (VLF)65536 Hz14 (16)-3
S-Matrix (E & B)S-Matrix0.5 Hz86614
HFA (E-2ch)spectrum-E (10 kHz - 10 MHz)18602
HFA (E/B)spectrum-E (10 kHz - 10 MHz)18602
HFA (E/B)spectrum-B (10 kHz - 100 kHz)18201

Table 2: Maximum Telemetry Plan
Instrument NameTypeTime ResolutionBitFrequency PointsChannels
EWO-EFD (DPB)spectrum (2-32 Hz)1 Hz8402
EWO-EFD (DPB)waveform8 Hz16-2
EWO-EFD (SPB)waveform4 Hz16-4
EWO-OFA/WFC (E)spectrum (10 Hz - 20 kHz)2 Hz8661
EWO-OFA/WFC (E)waveform (ELF)1024 Hz14 (16)-2
EWO-OFA/WFC (E)waveform (VLF)65536 Hz14 (16)-2
EWO-OFA/WFC (B)spectrum (10 Hz - 20 kHz)2 Hz8661
EWO-OFA/WFC (B)waveform (ELF)1024 Hz14 (16)-3
EWO-OFA/WFC (B)waveform (VLF)65536 Hz14 (16)-3
S-Matrix (E & B)S-Matrix0.5 Hz86614
HFA (E-2ch)spectrum-E (10 kHz - 10 MHz)18602
HFA (E/B)spectrum-E (10 kHz - 10 MHz)18602
HFA (E/B)spectrum-B (10 kHz - 100 kH)18201
  • DPB: double probe for electric field
  • SPB: single probe for spacecraft potential
  • OFA-E & B (a few Hz - 20 kHz, E 1ch & B 1ch) 2.1 kbps
  • High time resolution mode: 66 frequency points, Δt=0.5 s
  • High frequency resolution mode: 264 frequency points, Δt=4.0 s
  • Medium resolution mode will also be implemented.
Table 3: Specifications of the Antennas
AntennaWeightConfiguration
WPT-S (Ex+, Ex-)
(including extension system)
0.74 kg x 215 m x 2
Wire: 0.18 mmφ stainless
Spherical Probe: 6 cmφ, 50 g
MEFISTO-S (Ey+, Ey-)
(including extension system and preamplifiers)
0.89 kg x 215 m x 2
Wire: 0.1-0.3mmφ
Spherical Probe: 4 cmφ titanium
SC (Bx, By, Bz)1.12 kg20 cm x 3 axes
Extensible Mast2.5 kg288 mm x φ270 mm (withdrawn)
5318 mm x φ270 mm (extended)
Total6.88 kg

Table 4: Specifications of Electronics
ElectronicsWeightSpecifications
WPT-Pre (Ex+, Ex-)0.16 kg x 2DC - 10 MHz
SC-Pre (Bx, By, Bz)0.36 kg10 Hz - 500 kHz
PWE-E3.78 kgEFDDC - 64 Hz
WFC & OFA-E10 Hz - 20/120 kHz
WFC & OFA-B1 Hz - 20 kHz
MEFISTO-EDC - 32 Hz
SORBET2.5 kHz - 10 MHz
MAST/WPT-E1.31 kgMast/Antenna Extension Control
Wave MDP4.5 kg
Total10.27 kgPower: 35.5 W

Last Modified: