Design of a superconducting magnetic shield closed on both ends for a high-sensitivity particle detector

This work deals with the numerical design of a
high-efficiency superconducting magnetic shield required for a
high-sensitivity particle detector. This research was carried out
in the context of the ‘ABRACADABRA’ project aiming at
detecting hypothetical elementary particles called axions.
Axions are promising candidates to explain the particle nature
of the dark matter. The detector relies on a SQUID for
measuring the ultra-small oscillating magnetic field resulting
from the interaction between the axions and a toroidal DC field.
A magnetic shield is mandatory to reduce the ambient magnetic
field noise. Given the operating temperature (~ 1.2 K), the shield
is made of type-I superconductor. In this work we use numerical
modelling to determine the best topology for the shield and its
ability to screen both axial and transverse fields. Amongst the
geometries investigated (tubes or ‘swiss-rolls’ closed on both
ends) the best results are obtained with two semi-closed tubes
inserted in one another. This geometry is close to the shield of
the final prototype, made of two closed Cu tubes, spin-coated
with Sn (Tc = 3.72 K) and welded shut.