The scalar magnetometer conceived by Roland Lammegger and Christoph Amtmann at the Institute of Experimental Physics at TU Graz opens up new possibilities in magnetic field measurement thanks to its further development.

For just over two years, a scalar magnetometer developed by Graz University of Technology (TU Graz) and the Space Research Institute (IWF) of the Austrian Academy of Sciences has been on its way to Jupiter as part of ESA’s JUICE mission to discover liquid water beneath the surface of its icy moons. Roland Lammegger from the Institute of Experimental Physics at TU Graz, together with his colleague Christoph Amtmann and a team from the Space Research Institute, has now further developed the magnetometer he invented. Instead of only measuring the strength of magnetic fields, the improved version can also determine their direction, which was previously not possible with purely optical magnetometers.

Compass for magnetic field measurement

“Until now, there have only been theoretical considerations on how the direction of a magnetic field can be determined with a scalar magnetometer,” says Roland Lammegger. “With our device, we now have a kind of compass for measuring the magnetic field, which shows us the strength and direction. This further development could replace several measuring devices in the future. This would have several advantages for missions in space: less required space, lower weight and less energy consumption.”

At the heart of the magnetometer are rubidium atoms and their reaction to a magnetic field. If rubidium atoms are stimulated by a laser light, the frequency of the laser light changes. These changes allow conclusions to be drawn about the magnetic field strength. In order to obtain vector information, it was necessary to analyse the resonance amplitudes of the atoms in detail. The resonance amplitude is a measure of how strongly the rubidium atoms react to the laser light transmitted through them. There are several such resonances whose amplitudes are in a certain ratio to each other and contain the decisive angular information.

Endurance test of more than one month

In the tested experimental setup with two laser light beams angled towards each other, two resonances could be measured: one that is mainly parallel to each light beam and a second that has a maximum at right angles to it. By comparing the strength of these resonances, the angle of the magnetic field could be determined to the nearest angular minute. The team carried out its tests at GeoSphere Austria’s Conrad Observatory in Lower Austria, where it was not only possible to measure the Earth’s magnetic field, but also to generate test magnetic fields in order to analyse the magnetometer’s blind spots. The device ran for over a month to test its functionality and stability.

“If we ran the magnetometer with four laser beams instead of two, we could achieve even more accurate results,” says Christoph Amtmann. “However, this would greatly increase the mechanical and optical complexity and would be unsuitable for use in satellites at the current state of technology. Nevertheless, our development shows that this magnetometer is also promising for planetary probes with two laser beams – provided the magnetic field is not too weak. The fact that we have come this far is due in large part to our colleagues at the Space Research Institute, who have made a decisive contribution to the realisation of this new magnetometer with their expertise in hardware and software.”

The development of the new magnetometer was funded by the “1000 Ideas” project of the Austrian Science Fund FWF.