Practical techniques for making a two hole symmetric SQUID and for the adjustment of the point-contact weak link are described. The relation among the critical current, the room temperature resistance of the junction, and the Q decrease of a coil placed in one hole to obtain the optimum response, is discussed in terms of a simplified equivalent circuit. The optimum range of the room temperature resistance of the junction has been found to be 10-17Ω. Stability of the junction has been enhanced by mounting the device in a helium gas sealed can.
An apparatus for measurements of the heat capacity and the pressure coefficient of liquid He4 under pressure is reported. A tunnel diode oscillator is used to measure the change of the pressure. The frequency resolution and the reproducibility of the oscillator for pressure measurements are found to be 1×10-8 and 5×10-4, respectively. The temperature resolution of the system is 4×10-7K and the measurable range of pressure change is from 2×10-6bar to 30bar.
The applicability of diffusion bonding to superconducting joints is examined using a joint between two Nb-Ti plates. The joint made at 900°C yields critical current density nearly equal to that of base metal by post-bond treatment, i.e., cold-rolling plus aging process. The reduction in critical temperature of as-bonded joint was within 1K at all the bonding temperatures (600-900°C). The ultimate tensile strength of the joint made at 900°C reached that of base metal, but the breaking strain was reduced. The diffusion bonding is likely to be applied to joining superconducting Nb-Ti plates with an appropriate post-bond process.