Quantum-based MAGSCA aboard Juice

The magnetometer instrument on ESA's Juice mission to Jupiter, J-MAG, includes this quantum interference sensor, MAGSCA. This is the first time this precise but delicate technology has been used beyond Earth orbit. MAGSCA has been developed by the Austrian Academy of Sciences (OeAW) in partnership with Graz University of Technology, Austria, while the overall J-MAG magnetometer is the responsibility of Imperial College.

The magnetic field is a vector quantity which means it has size and direction. Magnetic sensors can be directional where they are sensitive to the field along a particular axis or absolute where they measure the overall strength of magnetic field. Absolute magnetic sensors are typically optical in nature using transitions between energy levels in atoms. Electrons dropping from a higher energy level to a lower one release photons of light just like in a light bulb. In the case of a light bulb the electrons are excited to the higher levels through the passing of an electric current through a wire.

Also, the reverse process can take place. When the light has the correct energy, it can be absorbed by atoms.

 The J-MAG instrument on JUICE is composed of three magnetic sensors, two direction sensitive fluxgate sensors and an absolute sensor called MAGSCA. The MAGSCA measures the absolute strength of the magnetic field also by using transitions between energy levels, this time in a Rubidium gas. In this case, it takes advantage of the Zeeman effect, which describes the splitting of atomic energy levels proportional to the magnetic field strength. The amount of splitting is sensed by optical pumping, whereby the atoms are 'pumped' by modulated laser light into a quantum mechanical superposition state which is composed of two lower-level ground states. The effect generates extremely narrow resonance features, whose central frequency is proportional to the ambient magnetic field strength. The sensing method is just based on natural constants, thus allowing highly accurate measurements.

The commissioning of MAGSCA in space included the very first detection of the quantum interference signal to measure magnetic fields in the MAGSCA sensor five million km away from Earth. This MAGSCA specific test measurement, together with the tracking of variations in the solar wind magnetic field, not only confirmed the good performance of MAGSCA but also of all three magnetic field sensors of J-MAG.