Magnetic Field Requirements for the TUCAN nEDM Experiment*

The TUCAN collaboration is preparing to make a new precision measurement of the neutron's permanent electric dipole moment (EDM), d_n, with an uncertainty of 1×10^-27e-cm, an order of magnitude better than the current world's best. To reach the goal sensitivity it is required to have highly uniform and well understood magnetic fields in the EDM measurement cells.

Ambient magnetic fields in the experimental area are on order of hundreds of μT. A magnetically shielded room will be used to reduce these external fields by a factor of 100,000 inside the room. This will be combined with ambient magnetic field compensation coils to further improve the shielding.

Inside the MSR a cosine theta coil will be used to provide the holding field for neutron precession during the measurement process. Additional trim and shim coils will be used to reduce non-uniformities in the magnetic field, with dedicated coils to be used for systematics studies.

In this presentation I will summarize our collaboration's strategy to characterize the magnetic fields in the MSR such that the combination of these active and passive methods can be used to modify the magnetic field inside the MSR to fulfill the measurement requirements.