Frequency and Time-Domain Analysis of a Superconductive Coaxial Line Using the Two-Fluid Model

Abstract

A miniature 80-ft superconductive coaxial line (Nb inner conductor 0.01 in. o.d., Pb outer conductor 0.034 in. i.d., polytetrafluoroethylene dielectric) has been analyzed in terms of the Gorter-Casimir two-fluid superconductivity model, considering the anomalous and classical cases (without relaxation effects) for the normal components. The dielectric and the metal flux trapping losses are assumed to be negligible. The 106−1012 Hz line attenuation and the 1–100 psec step responses are presented for the temperature range of 2.3°–10°K. Predictions are compared with the experimental results of several independent investigators. It is concluded that if the dielectric and the metal flux-trapping losses are negligible, then (1) The model provides bounds between which the responses of physically realized lines will fall, and (2) The normal conductivity of the conductors must be very good if the maximum bandwidth and minimum risetime are to be obtained.