1st Meeting for Satellite Overhauser Magnetometer

WMMSAT

Dr. Ivan Hrvoic, Ph.D., P.Eng.President, GEM Systems Inc.Canada

August 11-12, 2008 Boulder, Colorado

NGDC, 325 Broadway, Boulder, CO80305, DSRC Conference Room 1B402

Overview • Brief History of GEM Systems.• Theory of Operation of Quantum Magnetometers.• Polarization Theory.• Overhauser Effect.• Instrument Description. • Specifications of the Proposed Overhauser Magnetometer.• Sensor Bottle.• Signal Acquisition / Processing Electronics.• Statement of Work.• Conclusion

Brief History of GEM Systems GEM Systems has been incorporated in 1980 specializing in scalar magnetometers for Earth’s magnetic field.

• Grant from DSS in Ottawa for GSM-11 continuous Overhauser magnetometer in 1980• Series of grants O.H. various projects Ontario Industrial Research and Development.• Early development of PULSED mag/grad convenient for field work – mineral exploration, magnetic observations etc.• Potassium in 1990 – Russian research group in St. Petersburg - cooperation now Americanized components, new developments.• Very high sensitivity - Airborne - Ground - Observatories - Earthquake Research - 50 fT once per second 28 years focused on scalar mags; proton precession potassium, Overhauser

Theory of Operation of Quantum Magnetometers

Spin of charged particles (protons, electrons, some other nuclei)

= n p = n Ih/2

Only discrete orientations are allowed in magnetic field.

o = B Rotation (precession in the plane perpendicular to field)

1

2

B

M

Polarization Theory

Statistical distribution of orientations of the assembly of, say, protons prefers lower energy state. As a result a tiny magnetization in the direction of field is created

B

M

Assembly of protons(water, alcohol, etc)

Overhauser Effect

• Proton transitions 1-2 & 3-4

• Electron transitions 1-3 & 2-4

“Saturate” mixture via specified RF frequency so that electrons transfer their energy to protons

• Combined transitions 1-4 & 2-3

• Resulting in high polarization is 5000X gain

• Low Power

1

3

4

2

Scalar or dipole-dipole interaction.

1. RF ON

2. Short DC deflect Pulse

3. Free precession

4. No noise_1_ f

Pulsed Overhauser

Proposed Overhauser magnetometer model GSM-90S is a pulsed microprocessor based instrument consisting of: Omnidirectional Overhauser sensor • Signal Acquisition / Processing electronics

Instrument Description GSM-90S

Range of measurement: 15 μT – 65 μT (638 Hz – 2.8 kHz proton precession frequency) Resolution: 10 pTSensitivity: < 20 pT rmsAbsolute accuracy: < 0.2 nTRate of reading: 1 Hz (up to 5 Hz optional)Nyquist Bandwidth (no filtering)Heading error: < 0.1 nT Power consumption: < 12 V 1.5 WSensor weight: 1.35 kgSensor dimensions: 175 x 75 mm dia Electronics weight: 2.25 kg battery included Electronics dimensions: 223 x 69 x 240 mm

Sensor is isotropic (Omnidirectional ) – no dead zones. Signal amplitude variation over 360º spatial variation of the magnetic field direction is within 10%, With no offset reading.

Specifications of the Proposed

Overhauser Magnetometer

Sensor Bottle

Signal Acquisition / Processing Electronics

We plan to do the following steps in preparation for manufacture of proposed magnetometers:

1. Sensor Optimization. a) Standard sensor is Omnidirectional. Experiments with the shape and size of

the sensor will be carried out.

b) Ruggedization. The sensor must survive acceleration of the rocket launch. Probably

increase in the thickness of glass of the glass sensor bottle will suffice.

c) Argon bubble in the sensor allowing solvent expansion with temperature may change

the tuning of RF resonator. Reduction or elimination of this effect will be sought.

d) Influence of radiation. Free radical in the sensor liquid is a stable chemical. However,

we will investigate its resilience to expected radiation and the steps to reduce / eliminate it.

e) Operation of the sensor in vacuum is not expected to pose any problems. However, this

will be confirmed experimentally.

f) Rotational Dopper effect. Any possible tumbling of the satellite may affect the readings

of the magnetometer. Worst case rate of influence is about 23nT per 1 revolution per

second. If rotational motion of the satellite is known this effect can be reduced / eliminated.

Statement of Work

2. Cabling between sensor and electronics. Cables will be assessed for work in vacuum and under radiation. No major problems are expected.

3. Electronics. Starting from standard, commercial electronics following steps will be

done:

a) All components will be replaced by radiation tolerant ones. Additional radiation

protection may be designed in electronics enclosure.

b) Acceleration / vibration tolerance will be assessed experimentally. No serious

problems are expected.

c) Operation in vacuum will be experimentally confirmed.

Statement of Work (continue..)

4. Link to the system. a) Magnetometers will need power connection +12VDC at about 120 mA. Twisted pair robust wires will be used to bring power to the system.

b) Communication link. We expect serial link (RS232 or USB, ASCII format). Rate of data is low. c) Time synchronization pulse from GPS can be sent through serial link. Its precision of 1μ sec will keep magnetometer’s TCXO tied to absolute time. d) A series of ASCII commands to the magnetometer will control the operation of the magnetometer in full.

Timings of the above operations will be dependant on the overall schedule of satellite preparation. All of the above operations can comfortably be accomplished within 1 to 1.5 years or even less.

NOTE: GEM systems will try to engage a consultant experienced in space electronics / mechanics to facilitate the preparations.

Statement of Work (continue..)

Our standard, Overhauser magnetometer model GSM-90, very popular in magnetic observatories around the world can be adapted for satellite operation with relatively minor modifications.

Conclusion

Thank you for your attention.