Development of superconducting coaxial cables for cryogenic detectors

Fast readout with low noise is essential to apply superconducting detectors to such experiments as time-of-flight mass spectrometry or X-ray spectroscopy, where high counting efficiency is required. We have developed a thin seamless superconducting coaxial cable employing NbTi alloy in both of the outer and inner electrical conductors. The outer diameter is 1.60 mm, and both conductors are separated by dielectric material of PTFE. The coaxial cable revealed to become superconductive below about 10 K. The thermal conductance was measured between 0.4 and 6 K and consistent with literature. Performance at high frequency was also measured at 4.2 K. The attenuation was very small and less than 1 dB up to about 7 GHz. The effect of mechanical treatment to thermal and electrical properties of NbTi alloy seems to be small in the present forming process of coaxial cable.