centre national de la recherche scientifique

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUELaboratoire de Physique et Chimie de l'Environnement et de l’Espace

3A, avenue de la Recherche ScientifiqueF-45071 Orléans cedex 02, France

Phone: (33 2) 38 25 52 63; Fax: (33 2) 38 63 12 34; E-mail: [email protected]

EJSM JGO/RPWI Team Meeting, 26-27 Nov. 2009

Mutual Impedance MEasurements, MIME as part of the EJSM JGO/RPWI

Jean Gabriel TROTIGNON and Jean Louis Rauch

LPC2E, CNRS, Université d’Orléans, Orléans, France

EJSM JGO/RPWI Team Meeting, 26-27 Nov. 2009


Téléphone: (33 2) 38 25 52 63 Secrétariat: (33 2) 38 25 52 64 Télécopie (Fax): (33 2) 38 63 12 34 E-mail: [email protected]

Experiment Objectives

Principle of Measurements

Range of Measurements

Heritage

Instrument

Conclusion

Presentation Outline

Provide reliable/accurate measurements of total plasma density & thermal electron temperature, in Jupiter system environment (solar wind included);

Contribute to the study of the interactions between solar wind & Jupiter’s Magnetosphere, in particular around Ganymède and Callisto;

Give insight into thermal coupling between neutral & charged particles;

Detect plasma boundaries and identify plasma regimes;

JGO/RPWI/MIME Experiment Objectives (1 / 2)

Enable self and/or mutual impedances of LP-PWI and possibly RA-PWI electric antennae to be determined as a function of plasma environment;

Determine the effective length of these antennae (then allow E-field component of waves to be calibrated);

Possibly measure the physical/deployed length of antennae;

Contribute to onboard calibrations of LP-PWI, and maybe SCM and RA-PWI (calibration signal can be delivered)

cross-calibration between sensors.

JGO/RPWI/MIME Experiment Objectives (2 / 2)

MIME Principle of Measurements

A sinusoidal signal of known amplitude & frequency, coming from a current (or voltage) generator, is applied to antenna probe or wire shield, by short pulses (some ms), while induced voltage (or current) is simultaneously measured.

Antenna impedance Z = V / I is a function of frequency & plasma conditions.

Transmitted frequency varies step by step in a frequency bandwidth that includes the plasma frequency expected at Jupiter’s Magnetosphere (Ne proportional to Fpe

2).

Impedance spectra are computed onboard by FFT/DFT algorithms.

Plasma parameters, such as density and electron temperature, are derived from variations of both impedance modulus and phase close to Fpe.

Thermal electron temperature Te shall be determined provided

2 λD < L < a few tens λD ,

where L is the tip-to-tip antenna length and the plasma λD Debye Length

For the total electron density Ne, L must be higher than λD and can be higher than a few tens λD depending on the onboard FFT frequency resolution

Ne can be determined from resonance and/or wave signatures at the plasma frequency Fpe, the upper-hybrid frequency Fuh and Berstein mode frequencies Fqn

As a bonus, the magnetic field strength B can be derived from the electron cyclotron frequency Fce and its gyroharmonics nFce

Ne (cm-3) = Fpe2 (kHz) / 81Fce (Hz) = 28 B (nT)Fuh = (Fpe + Fce)1/2

Fpe (kHz) = 6687 Te1/2 (eV) / λD (cm)

MIME Principle of Measurements (cont’d)

4 March 2005, 22:12:39.14 UT, 0 dB ≡ 0.6 μV Hz1/2

Fpe = 468 kHz = 1.17 Fce Ne = 2,700 cm-3

616 kHz

Fuh896

FQ2

1232

FQ3

1624

FQ4

406 kHz

Fce

266 kHzInterference

812

2Fce1176

3Fce1568

4Fce

2,090 km altitude

MIME Range of Measurements




Fpe (kHz) Necm-3

10-3 eVλD (cm)

0.01 eVλD (cm)

0.1 eVλD (cm)

1 eVλD (cm)

10 eVλD (cm)

100 eVλD (cm)

0.285 0.001 740 2.35 103 7.4 103 2.35 104 7.42 104 2.35 105

0.705 0.006 300 949 3 103 9.5 103 3 104 9.5 104

1 0.012 210 670 2.1 103 6.7 103 2.1 104 6.7 104

2.1 0.05 100 320 103 3.2 103 104 3.2 104

2.23 0.06 300 950 3 103 9.5 103 3 104

6.7 0.55 100 316 103 3.2 103 104

7 0.6 300 955 3 103 9.6 103

10 1.23 21 67 210 670 2.1 103 6.7 103

21 5.4 100 318 103 3.2 103

22 6 300 960 3 103

67 55 100 316 103

70 60 300 955

100 123.5 2.1 6.7 21 67 210 670

210 540 100 318

220 300

670 5.5 103 100

1 000 1.2 105 0.2 0.67 2.1 6.7 21 67

3 500 1.5 105 0.06 0.2 0.6 2 6 19

9 000 106 0.02 0.07 0.23 0.74 2.35 7.4

Comparison between a 2 x 3 m long antenna (green) and a 2 x 1 m one (yellow);Ne and Te should be measured provided 0.5 cm ≤ λD ≤ 3 m (or 1 m)

Callisto (Gurnett et al., 2000)

Ne ~ 400 cm-3 (180 kHz) at 535 km

> 100 cm-3 (90 kHz) at 500 - 600 km

Iomospheric peak: 7 000 – 17 000 cm-3

(750 – 1200 kHz) at 30-50 km

Ganymede (Gurnett et al., 1996; Eviatar et al., 2001)

Ne ~ 200 – 300 cm-3 (130 – 160 kHz)at 1 000 km

Ne peak 400 - 2 500 cm-3

(180 – 450 kHz)

Expected MIME Range of Measurements

Frequency bandwidth: from a few hundred Hz* up to 3 MHz;

Debye length: from 0.5 cm up to 1-3 m (depending on antenna length);

Total plasma density: 0.01 – 1.5 105 cm-3;

Electron temperature: 0.01 – 100 eV.

The E-field antenna is assumed to be of the order of 2 to 6 m tip-to-tip long(the longer, the better)

* Lower-frequency signals can be produced for sensor calibrations (TBD)

Mutual Impedance Technique Heritage

The mutual/self impedance measurement technique has successfully been used, during nearly three decades, onboard ionospheric rockets and spacecraft (GEOS, VIKING, MARS 96, ROSETTA, and more recently BepiColombo/MMO).




ROSETTA/RPC/MIP Observations in the Earth’s Plasmasphere

Active: Impedance Modulus

Active: Impedance Phase

Passive: Natural waves

Mutual Impedance Technique Heritage (cont’d)

Numerical Simulations for BepiColombo/MMO

Both the capacitance and the resistance of the MEFISTO antenna exhibit a peak at the plasma frequency (=> density) and a “plateau” below (=> temperature).

Here, Debye length is 5 m, which is a typical value in solar wind close to Mercury (~30 m antenna tip-to-tip length).

Double probe

Double wire-shieldR0 /2

(analytic approx.)

(analytic approx.)

Double probe

Double wire-shield

R0 /2

(analytic approx.)

(analytic approx.)

Double probe

Double wire-shield

Double probe

Doublewire-shield

Mutual Impedance Technique Heritage (cont’d)

MIME Instrument




Global view of MIME instrument

electricantenna(e)

digital signalgenerator

signal acquisition

ADSP signal analyser(FFT, phase…)

signalcontroller

command word

clock

()

() also to SCM for calibrations (TBD)

Output signals of synthesizer are referenced to ground

Possible Electrical Interface: here AM²P-E to MEFISTO on BepiColombo/MMO

Safety relay

MIME outputswitch

synthesizer

MIME SensorElectronics

E-Field Sensor

Detail of possible interface with E-Field antenna(e) for wire and mutual modes

Electrical Interfaces : MIME to E-Field Antenna(e)

MIME may be composed of the following elements:

• The electronic board hosted in RA (it would allow MIME to be connected to every electric/magnetic sensors);

• Current probes hosted by E-field antenna deployment boxes (as in BepiColombo/MEFISTO ones);

• EGSE including data processing software.

RPWI/MIME Elements

“I " measured by MIME current probe“V " measured by LP/PWI

3 casescurrent injected on LP/PWI spheres,

voltage is measured

voltage injected on boom external shield,

current/voltage is measured

send calibration signal to a selected sensor:

LP/PWI or SCM

• V1 and V2 (2 channels)• V1 - V2 (1 channel)

• I1 and I2 (2 channels)• I1 - I2 (1 channel)• V1 - V2 (1 channel)• I1 - I2 and V1 - V2 (2 channels)

MIME possible working modes

A MIME measurement point contains 3 pieces of information:

• Reference spectrum (no transmission)• Power spectrum• Phase spectrum

from which Ne, Te, antenna impedances… are derived on ground.

Note: to increase SNR, each frequency may be transmitted n times depending on MIME working modes, and averages will

therefore be computed onboard.

MIME Measurement Point Definition

MIME power and mass ressources

Mass: 13 g eachPower consumption: 50 mWSize: 52 mm x 52 mm

Mass: 470 g (1.3 g / cm2)Power consumption: 1.3 W (1.6 W peak)Size: 247 mm x 147 mm

(BepiColombo/MMO/AM2P)

(Rosetta/MIP)

(BepiColombo/AM2P)

Mass: 240 g (0.8 g / cm2)Power consumption: 0.5 W (0.7 W peak)Size: A5

MIME Telemetry Ressources

Survey: 1952 bits / 60 s (33 bits s-1)

Ref. spectrum (passive): 64 frequency bins x 10 bits x 1Power spectrum: 64 frequency bins x 10 bits x 1Phase spectrum: 64 frequency bins x 10 bits x 1HK: 32 bits

Nominal: 6976 bits / 30 s (233 bits s-1)

Ref. spectrum: 96 frequency bins x 12 bits x 2Power spectrum: 96 frequency bins x 12 bits x 2Phase spectrum: 96 frequency bins x 12 bits x 2HK: 64 bits

Burst: 12 352 bits / 10 s (1 235 bits s-1)

Ref. spectrum: 128 frequency bins x 16 bits x 2Power spectrum: 128 frequency bins x 16 bits x 2Phase spectrum: 128 frequency bins x 16 bits x 2HK: 64 bits

E-Field Antenna Occupancy

1 MIME channel

Ref F0 F1 F126 F127

2 MIME channels

F1Ref F0 F126 F127

F1Ref F0 F126 F127

MIME emission 2 times shorter

ORFrequency repeated N times

Frequency repeated N/2 times

Example:

N = 24 (frequency step repetition factor; for a high signal to noise ratio)Frequency sweep = 128 different frequency steps (FFT: 256 samples)3 Frequency bands: 200 Hz – 20 kHz; 2 kHz – 200 kHz; 20 kHz – 2 MHz1 or 2 acquisition channels

Acquisition time (worst case): 855 ms (including time for the plasma to be stabilized)





J. G. Trotignon and J. L. Rauch

Conclusion

Thank you, first, for the invitation to participate in this exciting mission;

MIME may definitely contribute to the study of the Jupiter’ magnetosphere, in particular in measuring the electron plasma density and temperature, determining the effective length of electric antennae, helping out with in-flight sensor calibrations.

Application for funding has been submitted to CNES.

centre national de la recherche scientifique

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