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THEMIS-B: Search Coil Magnetometer

ResourceID
spase://SMWG/Instrument/THEMIS/B/SCM

Description

THEMIS-B Search Coil Magnetometer for measuring three dimensional changes in magnetic flux between 0.1 Hz and 4 kHz; the range extending to 8 kHz under certain conditions. The instrument is mounted on a ridged, retractable boom one meter in length extending from the top corner of the spacecraft (positive y-axis, negative x-axis in SPG coordinates). The SCM boom deploys at an angle of -167.9 degrees from the x-axis (SPG) and 10.1 degrees above the spin plane. Two of the probe's sensors are aligned within the spin plane of the spacecraft, with the B_x component 12.1 degrees from the SPG x-axis, the third being parallel to the spin axis completing a right handed orthogonal system. The three sensors are composed of two windings surrounding a core with a high magnetic permeability. The main winding, used for detection, consists of 51600 turns; the secondary winding introduces a flux feedback to damped the frequency response of the sensor and keep it independent of temperature variation. Multi-Layer Insulation keeps the probe thermally insulated while electrostatic shielding reduces its sensitivity to electric fields. Low noise at slower frewencies allows for sufficient overlap with Fluxgate Magnetomer (FGM) measurements (noise less than 0.76 pT/sqrt(Hz) at 10 Hz). Data from the SCM is passed through three pre-amplifiers, one for each sensor component, before going on to the DFB and IDPU for processing and digitization. Survey modes for the SCM are listed below in Table 1.

Table 1: SCM Telemetry Modes.

Filter Bank (fbk): Mean signal value over 6 frequency bands (4-2 kHz, 1-0.5 kHz, 256-128 Hz, 64-32 Hz, 16-8 Hz, 4-2 Hz); sampling rate of 1/16 to 8 S/s.
Fast Survey (scf): Waveform data for the 3 SCM components; sampling rate between 2 and 256 S/s, nominal value is 8.
Particle Burst (scp): Waveform data nominally at 128 S/s.
Wave Burst (scw): Waveform data nominally at 8192 S/s.
Particle Burst Spectra (ffp)
: Compressed FFT spectra in 16, 32, or 64 frequency bins; sampling between 1/4 to 8 S/s.
Wave Burst Spectra (ffw)
*: Compressed FFT spectra in 16, 32, or 64 frequency bins; sampling between 1/4 to 8 S/s.

*Only two available inputs between all 3 SCM and 12 EFI data signals.
**Only four available inputs between 3 SCM and 16 other data signals.

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Details

Version:2.0.0

Instrument

ResourceID
spase://SMWG/Instrument/THEMIS/B/SCM
ResourceHeader
ResourceName
THEMIS-B: Search Coil Magnetometer
AlternateName
THEMIS-B SCM
ReleaseDate
2019-05-05 12:34:56Z
Description

THEMIS-B Search Coil Magnetometer for measuring three dimensional changes in magnetic flux between 0.1 Hz and 4 kHz; the range extending to 8 kHz under certain conditions. The instrument is mounted on a ridged, retractable boom one meter in length extending from the top corner of the spacecraft (positive y-axis, negative x-axis in SPG coordinates). The SCM boom deploys at an angle of -167.9 degrees from the x-axis (SPG) and 10.1 degrees above the spin plane. Two of the probe's sensors are aligned within the spin plane of the spacecraft, with the B_x component 12.1 degrees from the SPG x-axis, the third being parallel to the spin axis completing a right handed orthogonal system. The three sensors are composed of two windings surrounding a core with a high magnetic permeability. The main winding, used for detection, consists of 51600 turns; the secondary winding introduces a flux feedback to damped the frequency response of the sensor and keep it independent of temperature variation. Multi-Layer Insulation keeps the probe thermally insulated while electrostatic shielding reduces its sensitivity to electric fields. Low noise at slower frewencies allows for sufficient overlap with Fluxgate Magnetomer (FGM) measurements (noise less than 0.76 pT/sqrt(Hz) at 10 Hz). Data from the SCM is passed through three pre-amplifiers, one for each sensor component, before going on to the DFB and IDPU for processing and digitization. Survey modes for the SCM are listed below in Table 1.

Table 1: SCM Telemetry Modes.

Filter Bank (fbk): Mean signal value over 6 frequency bands (4-2 kHz, 1-0.5 kHz, 256-128 Hz, 64-32 Hz, 16-8 Hz, 4-2 Hz); sampling rate of 1/16 to 8 S/s.
Fast Survey (scf): Waveform data for the 3 SCM components; sampling rate between 2 and 256 S/s, nominal value is 8.
Particle Burst (scp): Waveform data nominally at 128 S/s.
Wave Burst (scw): Waveform data nominally at 8192 S/s.
Particle Burst Spectra (ffp)
: Compressed FFT spectra in 16, 32, or 64 frequency bins; sampling between 1/4 to 8 S/s.
Wave Burst Spectra (ffw)
*: Compressed FFT spectra in 16, 32, or 64 frequency bins; sampling between 1/4 to 8 S/s.

*Only two available inputs between all 3 SCM and 12 EFI data signals.
**Only four available inputs between 3 SCM and 16 other data signals.

Acknowledgement
NASA contract NAS5-02099, V. Angelopoulos for use of data from the THEMIS Mission; also A. Roux and CETP for their work on the SCM.
Contacts
RolePerson
1.PrincipalInvestigatorspase://SMWG/Person/Vassilis.Angelopoulos
2.CoInvestigatorspase://SMWG/Person/Alain.Roux
InformationURL
Name
THEMIS Home Page
URL
Description

THEMIS Home Page.

InformationURL
Name
THEMIS-B Spacecraft
URL
Description

Spacecraft description from NSSDC database

InformationURL
Name
THEMIS-B Search Coil Magnetometer
URL
Description

Instrument (SCM) description from NSSDC database.

InformationURL
Name
The Search Coil Magnetometer for THEMIS
URL
Description

A. Roux et. al. In depth description of the THEMIS SCM.

InstrumentType
Magnetometer
InstrumentType
SearchCoil
InvestigationName
THEMIS Search Coil Magnetometer
ObservatoryID