Superconductivity & Particle AcceleratorS 2026

In high-energy physics, Nb-Ti-based superconducting magnets are traditionally cooled below 5 K using complex, large-scale cryogenic helium plants. However, for small-scale test facilities without access to such infrastructure, or for mobile superconducting magnet-based detectors, compact cryocoolers offer a promising alternative. The primary challenge of this approach is their limited cooling power, typically a few Watts at 4.2 K. To accommodate this design limitation, heat leaks to the cold mass must be strictly minimized. This is effectively achieved using hybrid current leads, where High-Temperature Superconductors (HTS) reduce both Joule heating and conductive heat loads to the winding in the cold mass made with Low-Temperature Superconductor (LTS). Such leads require efficient thermalization at intermediate temperatures, which can be driven by cryocoolers.

This work presents the design, development, and experimental evaluation of a hybrid current lead system based on BSCCO-2223, designed for a nominal current of 3 kA. Each lead consists of a brass normal-conducting section, an HTS section, and a low-temperature Nb-Ti shunt interconnecting the leads. Thermalization is achieved through two remote cooling circuits driven by separate cryocoolers. The first cryocooler is used to drive a helium gas circulation loop intercepting heat from the normal-conducting part of the current leads, maintaining the top of the BSCCO-2223 component at approximately 56 K. The second cryocooler is used to cool the Nb-Ti section relying on helium condensation and passive liquid helium circulation.

The experimental results focus on the electrical and thermal behaviour of the current leads and their associated cryogenic thermal interfaces. Finally, the measured cooling performance from room temperature down to 4 K is discussed and compared with theoretical predictions, demonstrating that the proposed configuration provides a practical solution for cryocooler-based operation of superconducting magnets.