Development of a Low Heat Leak Current-Lead System

Abstract

This paper describes a low heat leak current-lead system for a high temperature superconducting magnet which is refrigerated by conduction cooling and operated in a persistentcurrent mode. Under the condition that the current lead is cooled by conduction without gas cooling, we investigated the current-lead structure with which the heat load to the cryocooler is sufficiently low. The current lead consists of two parts. One of them spans the temperature interval between room temperature and around 70 K. The other spans the temperature interval between around 70 K and the lower end temperature. The former is made of copper alloy and the latter is made of HTS superconductor. To decrease the heat leak to a thermal anchor in the 70 K region, a detachable joint is installed in the copper alloy part. The driving mechanism for the joint is set in the room temperature region. An ultrasonic rotation motor, which works in the vacuum and the magnetic field, is adopted for the driving mechanism. We designed and constructed a detachable current lead of 600 A class, and obtained a test result that the heat leak to the thermal anchor is sufficiently low.

Cryocooler cooled HTS current lead for a 35kJ/7kW-class high-Tc SMES system

“…As for a superconducting magnet cooled by conduction cooling, all heat leaks are loaded on a cryocooler. It is essential to minimize heat leak into the cryostat of a superconducting magnet for reducing the refrigeration power load and thus the cost of refrigeration [1][2][3]. A current lead, which replaces the lower temperature part of conventional metallic lead with a HTS current lead, can help reduce the heat leak since HTSs are good electrical conductors with much lower thermal conductivities than that the normal metals are [4].…”

Persistent Current HTS Magnet Cooled by Cryocooler (3)—HTS Magnet Characteristics

“…So far, we have improved the performances of racetrack formed single-pancake coils, especially the n-value in a low electrical field region from to . We also developed a persistent current switch (PCS) made of a YBCO thin film [4] with a higher switching speed and detachable current leads for low heat leak to a cryostat [5]. Integrating these devices, a persistent current HTS magnet of the same size as a magnet for a Maglev train was fabricated and evaluated.…”