Thermal effects on the Josephson series-array voltage standard

A series-array voltage standard containing 2,076 Josephson junctions has been operated in a liquid helium bath maintained within a refrigerated Dewar over the temperature range 1.56K ≤ T ≤ 4.54K. No systematic variation in the array voltage near 1.018V with temperature was detected over this entire range, indicating that any temperature coefficient of the array voltage must be less than 2×10^-8 V/K. The critical current and gap energy of the weakest junction within the array in the absence of millimeter wave power were measured as a function of temperature over this same range. The noise sensitivity of the array was observed to change abruptly but by a small amount as the helium bath was pumped superfluid. Voltage calibrations were unaffected by the bath's superfluid transition.