The geomagnetic observatory in Brorfelde has an important instrument calibration facility that includes a double 2 by 2 meter Helmholtz coil, wherein magnetometers are exposed to a controlled magnetic field that adds to the background natural geomagnetic field. It would be a significant improvement if the natural field variations could be automatically cancelled out, by suitably varying the output of the Helmholtz coil. In this project we propose to achieve this by taking advantage of real-time observations of the natural field made by a nearby 3-axis fluxgate magnetometer.
The goal of this project is to develop a system to control the coil power supply to very high precision using magnetometer data as input, keeping the magnetic field in the middle of the coils constant (zero) within 1 nT. It will involve work both at the geomagnetic observatory in Brorfelde and at the magnetometer lab in Lyngby. We will first determine a transfer function for the control system (considering both frequency and delay) and then, after implementation, characterize its stability and noise level. As well as a zero field control system, we plan to extend the technique to simulate other magnetic fields, including specified constant fields, fields with a defined time variation (e.g. sine or square waves at different frequencies), and even dramatic magnetic events. Such capabilities will greatly extend the range of the magnetometer calibration facility and aid the development of the next generation of Danish fluxgate magnetometers.
In collaboration withDTU Space