Development of a miniaturized SQUID measuring systems for an experiment to measure the electric dipole moment of the neutron

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In a next generation experiment to measure the electric dipole moment of the neutron (nEDM) accurate control of magnetic fields is crucial. In particular, the vertical gradient through the neutron storage chamber needs to be determined precisely to avoid so-called geometric phases, which appear in combination with systematic trajectories of stored ultra-cold neutrons (UCN) in the chamber. Those are interpreted as false EDM Signals and have been observed on the level of 10-26 ecm in the previous generation of experiments. Based on recently developed large volume 3He spin precession chambers, such a gradient can be determined with great accuracy. However, also these 3He chambers must be read out with means of magnetometers. Investigations at PTB Berlin already showed that SQUID magnetic field sensors are best suitable for this purpose, as their noise characteristics at typical precession frequencies (10-50 Hz) are < 2 fT/ . Within the framework of this proposal a miniaturized SQUID System should be developed to read out 3He precession Signals. In addition it should be capable of delivering directional information of magnetic fields in vicinity of the UCN precession chambers and should act as the central component of a 129Xe magnetometer. Next to the use in the nEDM experiment, the new SQUID cryostat potentially has a variety of applications in various fields of research, e.g. biomagnetism.