Lightweight Superconducting Magnets for Low Temperature Magnetic Coolers

NASA's future science missions to investigate the structure and evolution of the universe require efficient, very low temperature coolers for low noise detector systems. We propose to develop a highly efficient, lightweight Active Magnetic Regenerative Refrigeration (AMRR) system that can continuously provide remote/distributed cooling at temperatures of about 2 K with a heat sink at about 15 K. The AMRR system uses three novel design features to achieve a large cooling capacity and very high thermal efficiency: a vibration-free, reversible cryogenic circulator; innovative micromachined regenerators; and lightweight superconducting magnets. The superconducting magnet uses low-current superconducting wires and a unique winding arrangement to enable an AMRR system to achieve high thermal efficiency. In Phase I, we selected an optimum superconducting material for the magnet and developed its electrical and structural support subsystems. Based on the performance characteristics of the magnet, we optimized the magnetic field and showed by analysis that the AMRR system driven by such a magnetic field will be able to achieve high efficiency. In Phase II, we will build and characterize a superconducting magnet, assemble a brassboard AMRR system with a circulator and an active magnetic regenerator, and demonstrate the system performance under prototypical conditions. In Phase III, we will assemble a fully integrated Engineering Model AMRR system and demonstrate its performance.