This thesis describes the development of several systems based on the Cryogenic Current Comparator with optimum SQUID readout, for current and resistance metrology applications. the CCC-SQUID is at present the most accurate current comparator available. A (type I) CCC consists basically of a superconducting tube containing two sets of windings N1 and N2, carrying the two currents I1 and I2 to be compared. As a result of the Meissner effect, a screening current equal to (I2N2-I1N1) circulates in the tube (overlapped “like a snake swallowing its own tail” to shield the windings from the sensing circuit). The flux associated to the unbalance current is coupled to a SQUID, the most sensitive flux sensor available nowadays. The SQUID is basically a superconducting ring interrupted by one (rf SQUID) or two (dc SQUID) weak links called Josephson junctions. The device works basically as a flux-to-voltage converter.
|Award date||1 Mar 2002|
|Place of Publication||Enschede|
|Publication status||Published - 1 Mar 2002|