Precision field characterization for the next generation measurement of the neutron EDM

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In this proposal we plan to realize a magnetic field measurement system for a next generation measurement of the neutron's electric dipole moment (EDM) with a sensitivity of 10-28 ecm. The system will be deployed for two purposes: (i) characterization of all kinds of fields from field coils and components inside the magnetically stabilized environment offline during installation and after of each component at their final location. This is in particular important for the EDM chamber parts, UCN optics and hardware inside the vacuum chamber. The figure of merit for the magnitude of contaminations is maximum 1 pT at 3 cm distance for inner components, giving rise to geometric phase effects. Goal (ii) is the measurement of magnetic fields during the EDM measurement online. Here, the long-term performance on a 100 fT level per sensor and the resolution of field direction on the 10-4 rad tilt-level is necessary. This helps to track changes of the shape of gradients from large and small localized sources using vector information while the experiment is operating. As all other in-situ (co-)magnetometers only provide averaged information, this is critical for the understanding of systematic effects. For this purpose we made tests with a fully optical Cs magnetometer system that is perfectly suitable for in-situ measurements online and offline without producing noise due to induced RF or magnetized hardware components. Within this project we would like to develop a set of such probes for both goals in 3 subsequent stages. Stage 1 is further optimization of sensors and their operation modes, stage 2 is the installation of a larger set of sensors on site for offline and online field mapping with commissioning and stage 3 is the operation, characterization and test against other systems.