Line-integral corrections in Larmor-precession devices

Abstract

Larmor-precession devices need homogeneous line integrals of the magnetic field along the neutron trajectories over the beam cross section. Line-integral inhomogeneities must be homogenized or corrected in order not to spoil the initial polarization. They can be corrected by two sets of coils. The first set of coils generates a vertical field gradient opposite to the precession-field gradient. Actually, these coils transform a gradient of the line integral in the field direction to a direction perpendicular to it. This last gradient is corrected by the second set of coils, which has a homogenous field in the vertical direction and a parabolic shape in the perpendicular direction. The corrected beam has a polarization of 0.82 for a beam cross section of 10×15 mm2 whereas, for the uncorrected beam, the polarization is 0.20.