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Guiding fields development for the TUCAN nEDM Experiment Klemets, Emma Myra


The TUCAN (TRIUMF Ultra-Cold Advanced Neutron) neutron electric dipole moment (nEDM) Experiment is looking to measure the nEDM with a goal sensitivity of 1 x 10⁻²⁷ ecm. The discovery of a non-zero nEDM would help explain the matter-antimatter imbalance seen in our universe. The TUCAN nEDM experiment requires polarized ultracold neutrons to be stored in a volume with precisely known electromagnetic fields. To achieve high counting statistics, a large number of neutrons and high degree of neutron polarization are required. For this, the neutron polarization needs to be conserved during neutron transport, leading to the prerequisite of adiabatic transport. Adiabatic transport is when there are no strong gradients or zero field transitions such that the neutron polarization can stay aligned with the magnetic field along the neutrons’ path. An adiabatic transport system can be used to achieve this by superimposing additional fields to existing background fields to tune field properties. The development of the adiabatic guiding fields subsystem consists first of understanding adiabatic transport as quantified by the adiabatic parameter. The derivation of this parameter, and its relation to the resulting polarization of neutron ensembles, is explored in this work. Requirements on the minimum value of the adiabatic parameter for a desired minimum polarization have been set, which are then the main guidelines while designing the guide coils themselves. The adiabatic parameter is dependent on the magnetic field and angular gradients, and a thorough mapping of the guide region will be necessary for the final guiding fields design. Currently, many parts of the TUCAN nEDM Experiment are in the design phase, increasing the difficulty of obtaining meaningful field maps. In the meantime, a Magnetic Test Environment has been built and tested to model many of the major magnetic components. This setup was used to develop a mapping and analysis procedure in order to test prototype guiding coils. The coils tested were successfully able to create regions of controlled fields giving proof of principle. Future work should continue into the design and automation of this guide coil design method as more of the experimental region is built.

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