Critical current measurements at electric fields in the pV m/sup -1/ regime

Persistent current joints between technological superconductors

“…Whilst an understanding of the V-I characteristics at high electric fields will add to an overall understanding of the behaviour of these joints (including quench characteristics), that V-I trends observed at high electric fields are not generally applicable at lower electric fields. The practical voltage measurement floor for the four-probe technique is typically ∼10 −9 V, and so it cannot generally be employed to directly measure the V-I characteristics of wires and joints under PM conditions [28,29]. An alternative technique, IRT, is instead employed to measure V-I characteristics at higher sensitivities.…”

“…The IRT method, otherwise known as the current or field decay method, measures V-I characteristics from the temporal-decay of currents flowing in inductive superconducting circuits. This technique has been used to analyse loss mechanisms in technological wires [28,29] and is the standard tool for characterising joints [24,[30][31][32][33][34][35].…”

Rapid characterisation of persistent current joints by SQUID magnetometry

“…Also of interest is the critical current at a certain resistance criterion-I c (B,T). The measurement of persistent current resistances far exceeds the sensitivity limit of the four probe technique, for which voltage measurement sensitivity (∼1 nV) limits resistance sensitivity to ≳10 −12 Ω [6]. In light of this limitation, inductive resistance testing (IRT, otherwise known as the current decay method) has instead been widely used to characterise joints [7][8][9][10].…”

“…The IRT technique measures the decaying magnetic field produced by a current flowing around a small superconducting sample coil (of self inductance L), closed by the joint of interest. In most cases, the resistance in the circuit (R) is dominated by losses in the joint, which typically has inferior superconducting properties to the parent wires [6]. The temporal decay of the field produced by the sample coil (or equally the coilʼs magnetic moment (μ) or current (I)) follows the standard form for L-R circuits…”

A new concept for developing a compact joint structure for reducing joint resistance between high-temperature superconductors (HTS) and low-temperature superconductors (LTS)

“…Ohmic resistance measurements on the boat joints were marginal with resistance ranging below 1 nΩ. To measure further smaller resistance, a current decay measurement would be necessary to estimate the resistance [30][31][32]. The voltage started to increase exponentially against current in high fields of over 1.0 T, which indicates that the Pb-Bi matrix started to change into the normal conducting state from the superconducting state.…”