Speaker
Description
Magnetic-field uniformity is a critical requirement for neutron electric dipole mo-
ment (nEDM) experiments, where magnetic-field gradients can reduce neutron spin
coherence and contribute to systematic frequency shifts. The TUCAN (TRIUMF Ultra
Cold Advanced Neutron) EDM experiment at TRIUMF requires a stable and homoge-
neous magnetic-field environment for precision neutron spin-precession measurements.
To support this goal, a prototype shim coil system has been developed and installed
inside the TUCAN magnetically shielded room to provide controlled magnetic-field
corrections and to generate selected harmonic gradient modes. The system consists
of a 54-coil cubic array, with nine square coils installed on each of the six inner faces
of the MSR, driven by a modular 64-channel bipolar current supply. Coil-current set-
points are calculated using a linear response matrix generated by COMSOL and a
singular-value-decomposition pseudoinverse, allowing target gradient fields to be pro-
duced in the region of interest. The system was characterized using three-axis fluxgate
magnetic-field scans along a central scan axis, and the measured field profiles were
compared with COMSOL-based simulations that include the magnetic response of the
shielded room. Results of the comparisons indicate that the coil system is function-
ing well, although additional studies will be needed once a better magnetic mapping
system can be used. The results are sufficient to validate the construction and control
methods used for the coils. The coils will be modified to fit within the B0 coil assembly
once it is complete.