A 4 T HTS Magnetic Field Generator, Conduction Cooled, for Neutron Physics Spectrometry

Abstract

This paper is concerned with the analysis of thermal and magnetic design of a high-uniformity magnetic field (HUMF) electromagnet using high temperature superconducting (HTS) coils in Helmholtz arrangement, for nuclear physics experiments. The sample, exposed to a neutron pulse, is placed in the HUMF, and detectors are registering the emerging radiation. The 4-T dipole HUMF electromagnet system is conduction cooled using a closed-cycle Gifford-McMahon cryocooler. A second cryocooler is used to keep the sample temperature in the 4.2-300 K range. The Helmholtz coils are made of high temperature superconductor (HTS) tape of YBCO type, and are mounted in a special-shaped cryostat. Numerical experiments are performed to assess the magnetic field uniformity. This paper relies on a 3-D computer-aided design model of the electromagnet prototype. They unveil the magnetic field spectrum and the heat paths within the aggregate structure of the magnet system. The "warm” channel crosses the magnet axially and the HTS field winding must be kept within safe temperature limits or the HTS may exit the superconductive state. Therefore, cryocooling is used to remove the heat influx from the ambient. The numerical modeling of the heat transfer phenomena inside the magnet system reveals the temperature distribution and thermal loads for cryocoolers.