High-temperature superconductor cryogenic current comparator

NIST is developing a cryogenic current comparator (CCC) to operate at 77 K, using high-temperature superconductor (HTS) ceramic shielding material and an HTS-based superconducting quantum interference device (SQUID) detector. The shielding properties of at least two polycrystalline oxide HTS materials appear sufficient for use in a high-accuracy CCC. A measurement of current-linkage error, a figure of merit for CCC devices, is made for one type of HTS CCC. The design of a second HTS CCC which uses improved magnetic shielding is described.<>