Spin Dressed Relaxation and Frequency Shifts from Field Imperfections.

Critical dressing, the simultaneous dressing of two spin species to the same effective Larmor frequency, in principle, maximizes the sensitivity of the nEDM@SNS. The benefits of critical dressing are achieved at the expense of generating a large uniform oscillating field. Due to inevitable imperfections of the fields generated, the benefits of spin dressing may be lost from additional relaxation and noise. In this analysis the subject of relaxation and frequency shifts of neutrons and ³He in a spin dressing field are approached with simulations and theory. Analytical predictions are made from a new quasi-quantum model that includes gradients in the holding and dressing fields. The results are compared with a Monte Carlo simulation coupled with a 5^th order Runge-Kutta integrator. Comparisons are presented as well as a set of optimized parameters that produce stable critical dressing for a range of dressing frequencies, as well as pulsed modulation parameters for maximum sensitivity.