Systematic studies of the effect of a bandpass filter on a Josephson-junction noise thermometer

Measurements of the effect of a bandpass filter on the noise of an R-SQUID were made. Comparison of the data with a model for the effect indicates good agreement to within the measurement imprecision, although the fitted parameters show some discrepancies. The observed discrepancies influence the temperatures derived from the data by less than 0.1%. Additional studies indicate that the observed noise spectrum is white and uncontaminated to the level of 0.1% by extraneous noise. Finally, the reproducibility of repeated measurements of the noise within an experimental run is at least 0.1%, while the reproducibility between runs, as judged by superconducting fixed points and a /sup 3/He melting curve thermometer, are no worse than 0.3%. It is concluded that an R-SQUID noise thermometer is capable of producing a temperature scale from 6.3 mK to 520 mK which is accurate to 0.1%.