Teranishi Y.,Metropolitan Institute of Technology |
Kasai S.,Coax Co.
Journal of Superconductivity and Novel Magnetism | Year: 2013
Semirigid coaxial cables with seamless metal shields are promising for readout from sensitive devices operating below liquid helium temperature. Low thermal conduction of such cables are also essential to reduce heat penetration into cryogenic temperature. We have developed thin semirigid coaxial cables employing niobium-titanium and niobium in both center and outer conductors, taking advantage of low thermal conductivity and extreme small electrical resistivity of superconductors. We assembled an adiabatic demagnetization refrigerator and measured thermal and electrical characteristics of those superconducting coaxial cables below Tc. Thin niobium coaxial cable with an outer diameter of 0.86 mm showed two-orders lower thermal conduction than expected, which is considered as the effect of impurity of niobium and forming process. Small attenuation was observed up to high frequency above 10 GHz at 3 K. © 2013 Springer Science+Business Media New York.
Kushino A.,Hokkaido University of Science |
Kasai S.,Coax Co.
Journal of Superconductivity and Novel Magnetism | Year: 2014
We are developing thin semi-rigid cables with outer diameters less than 1 mm, for accurate readout of cryogenic applications. The center conductor is separated from seamless metal outer conductor by dielectric material, polytetrafluoroethylene (PTFE). In order to suppress heat penetration through the cables into cryogenic stage, we used low thermal conductivity normal conducting alloys or superconductors as the material for both center and outer conductors. And to cut high frequency noise components in readout, we adopted bilayer structure in the center conductor, where superconducting wire with a diameter of 178 μm made of niobium-titanium (NbTi) was clad in normal conducting alloy, cupronickel (CuNi) of 13 μm thickness. We also used CuNi pipe with an outside diameter of 0.86 mm as the outer conductor. From the results of thermal conductance and attenuation below the critical temperature of NbTi (∼9 K), we confirmed that this kind of semi-rigid cable can work as a low-pass filter used at cryogenic temperature. The -3 dB cutoff frequency of 1 m length cable was observed at ∼500 MHz, above which attenuation became significant because of the skin effect and large electrical resistivity of CuNi cladding. © 2014 Springer Science+Business Media New York.