Speaker
Description
The TUCAN collaboration is preparing to make a precision measurement of the neutron's permanent electric dipole moment, $d_n$, with a sensitivity of $\sigma(d_n)\leq10^{-27}e\cdot cm$. To reach the goal sensitivity it is required to have highly uniform and well understood magnetic fields in the measurement cells. With ambient magnetic fields on order of hundreds of $\mu \rm T$, passive magnetic shielding combined with compensation and shim coils are required to achieve the needed field uniformity
($\sigma(Bz) < 40\,\rm pT$) and stability over several measurement cycles.
A magnetically shielded room (MSR) will reduce external fields by a factor of $100,000$, and provide magnetic fields with gradients of $0.1-1\,\rm nT/m$ in its interior. Inside the MSR a cosine theta coil will be used to provide a $1\mu\,\rm T$ holding field in which the neutron's spins will precess 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 obtain sufficient information about the shape and strength of the magnetic field such that it can be modified and characterized to fulfill the measurement requirements. This covers items such as ambient field compensation coils around the MSR, highly accurate offline magnetic field mapping inside the MSR, and high precision magnetometry and co-magnetometry during the actual measurement of $d_n$.
