Ultracold neutron accumulation in a superfluid-helium converter with magnetic multipole reflector

TL;DR

This paper investigates how magnetic multipole reflectors can enhance ultracold neutron accumulation in superfluid helium, potentially increasing density, polarization, and reducing wall losses for neutron sources.

Contribution

It presents a detailed analysis of UCN accumulation considering magnetic fields, introducing a method to optimize neutron density and polarization in superfluid helium converters.

Findings

Magnetic multipole fields increase saturation UCN densities.

Magnetic storage mitigates wall loss effects.

Potential for highly polarized UCN samples.

Abstract

We analyze accumulation of ultracold neutrons (UCN) in a superfluid-helium converter vessel surrounded by a magnetic multipole reflector. We solved the spin-dependent rate equation, employing formulas valid for adiabatic spin transport of trapped UCN in mechanical equilibrium. Results for saturation UCN densities are obtained in dependence of order and strength of the multipolar field. The addition of magnetic storage to neutron optical potentials can increase the density and energy of the low field seeking UCN produced and serves to mitigate the effects of wall losses on the source performance. It also can provide a highly polarized sample of UCN without need to polarize the neutron beam incident on the converter. This work was performed in preparation of the UCN source project SuperSUN at the ILL.