Field Gradient Cancellation Technique for the LANL nEDM Experiment

The search for the permanent electric dipole moment of neutron (nEDM) has the goal of exploring sources of beyond standard model CP violating physics. The room temperature LANL nEDM experiment was proposed to push the upper limit of nEDM to $3 \times 10^{-27}$ e$\cdot$cm (68\% confidence level). Achieving this substantially high sensitivity requires a highly uniform magnetic field which lowers the systematic uncertainty associated with the field non-uniformity below the precision goal of the experiment. The geometric phase false EDM effect is the primary consideration for the field uniformity requirement and it demands that the magnetic field gradients to be controlled below $0.3$ nT$\cdot$m$^{-1}$ at the nominal $B_0$ field of 1 $\mu$T. I will describe the technique and the design of the proposed gradient coils to cancel first order and higher order magnetic field gradients to achieve the field uniformity requirements of the LANL nEDM experiment.