Performance of an ultra-thin superconducting solenoid for particle astrophysics

An extremely thin superconducting solenoid with a main diameter of 0.9 m and a length of 1.4 m has been fabricated for a balloon borne experiment in Antarctica to study anti-particles in cosmic rays. The solenoid has a 0.8 m diameter warm bore where a magnetic field of 0.8-1.0 T is induced. The coil was wound with mechanically advanced aluminum stabilized superconductor recently developed by using micro-alloying Ni into a pure aluminum base and by cold-work hardening, and consequently the electromagnetic force may be fully supported by the coil itself without any additional support structure. The solenoid was successfully charged up to 1.05 T without any premature quenches. Despite measured strains were beyond 1500 micro-strain, the coil behaved elastically. Because of relatively small RRR of 110, the quench energy is distributed rather unevenly, and a temperature difference of over 100 K was observed. Nevertheless, it was found to be safe to quench the magnet.