Superimposed electric/magnetic “dipole moment comparator” lattice design

Abstract

In contrast to a “single particle table-top trap”, an essential feature of a storage ring “trap” is that 1010 or more particles can have their spins aligned in a polarized beam.This is a nunber of polarized particles large enough for the beam polarization to be detected externally,and fed back to permit external control of the beam polarization. Though the table large enoughfor any such “storage ring trap” is quite large, the level of achievable spin control, thoughclassical, not quantum mechanical, can be comparable to the control of one or a small number ofpolarized particles in a low energy trap.Motivated to investigate time reversal invariance, especially the detection of non-zero electricdipole moments (EDMs) thispaper describes the design of a low energy storage ring having the superimposed electric and magneticbending needed to “freeze” the spins of polarized beams. For electrons (of either sign) and protonsthe spins can be frozen with all-electric bending but, in general, superimposed electric/magnetic bending isrequired. Since constructive bending superposition in one direction implies destructive superposition inthe other direction, counter-circulating beams must differ, either in particle typeor momentum, in order for their orbits to be identical.For globally frozen spin operation the bunch polarizations remain constant relative to the momenta,for example remaining parallel to the circuating beam momentum vectors. With superimposed electric and magnetic bending,the globally frozen spin condition can be met over a continua (specific to particle type) of E/B ratios. When thiscondition is met, the out-of-plane, EDM-induced precession accumulates monitonically, which is obligatory forproducing a measurably large EDM signal. As Koop has explained, the EDM signal will still accumulate if thepolarization is allowed to “roll like a wheel” around a radial axis.