EXPECTED PERFORMANCE OF A RADIOFREQUENCY BIASED R-SQUID NOISE THERMOMETER BELOW 6-MK

The noise and circuit impedance of an R-SQUID noise thermometer (i.e., a circuit composed of a Josephson junction shunted by a resistor R) h ave been extensively studied as a function of the applied rf and dc bi as currents. Over the temperature range studied (6.3 mK to 740 mK), th e noise and impedance were fit very well by predictions of the Resisti vely-Shunted Junction (RSJ) model and the R-SQUID was used to successf ully define an absolute temperature scale over this range. On the basi s of these results, the performance of the noise thermometer is evalua ted at lower temperatures, particularly at the fixed points defined by the phase diagram of He-3. It is concluded that the R-SQUID should be capable of defining such temperatures down to 1 mK with an accuracy t o approximately 0.1%.