Implementation of the frozen-spin technique for the search for a muon electric dipole moment

Applying the frozen-spin technique in a compact 3 T solenoid will enable a search for the muon electric dipole moment (EDM) with unprecedented sensitivity, improving upon the current direct limit by approximately a factor of 1000. After injection of a selected muon, a pulsed magnetic field will reduce its longitudinal momentum sufficiently to be confined within a static weakly-focusing magnetic field and maintain a closed circular orbit. A precisely tuned radial electric field will cancel the spin precession induced by the muon's anomalous magnetic moment, a = (g - 2)/2, relative to the orientation of the momentum. In this configuration, the EDM becomes the only remaining inherent source of relative precession. Asymmetry in the direction and energy of positrons emitted from muon decay provides an experimental signature of such precession. In the first of two phases, 28 MeV/c muons from the 7rE1 beamline at PSI will be used to demonstrate the systems necessary for injecting and trapping muons, tuning fields to the frozen-spin condition and reconstructing positron trajectories. Designs for the coils producing the pulsed magnetic field and the electrodes applying the frozen-spin electric field are currently being evaluated with simulations and prototypes. These systems must be designed in parallel, especially due to the impact of eddy-currents induced in the electrodes by the pulsed magnetic field. The electrode design must minimise eddy-currents to preserve the field strength of the pulsed field responsible for muon trapping, while maintaining the electric field uniformity necessary to achieve the sensitivity goal. This article summarises some of the efforts underway to address these design challenges.