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TT: Fachverband Tiefe Temperaturen

TT 17: Matter at Low Temperature: Measuring Devices, Cryotechnique

TT 17.2: Vortrag

Dienstag, 26. Februar 2008, 14:15–14:30, H 2053

Practical SQUID-based noise thermometers for millikelvin temperatures — •Jörn Beyer, Dietmar Drung, Alexander Kirste, and Jost Engert — PTB, Berlin, Germany

We are developing SQUID-based noise thermometers aiming at compact and easy-to-use, linear and fast noise thermometers to cover the temperature range of dilution refrigerators, i.e., from about 10mK to 4K. The two types of thermometers we investigate are the Magnetic Field Fluctuation Thermometer (MFFT) and the Current Sensing Noise Thermometer (CSNT). In both the MFFT and the CSNT the thermally induced motion of charges in a metallic temperature sensor causes thermal magnetic flux noise detected by a SQUID sensor. The temperature of the metal is extracted from the thermal noise signal via the Nyquist theorem. In our MFFT and CSNT implementations the metal temperature sensor and the SQUID sensor are placed at the same temperature stage. In the case of the MFFT, the temperature sensor is a bulk Copper part and thermal magnetic field fluctuations above its surface are measured inductively by a multiloop SQUID-gradiometer. For the CSNT, the temperature sensor in form of a thin film resistor and a SQUID current sensor to measure the resistor current noise are integrated on a silicon chip. We present a comparison of our MFFT and CSNT configurations in terms of their sensitivity, speed, and linearity. We discuss the design of the temperature sensors and SQUID sensors, thermal anchoring and shielding of external interferences for the MFFT and CSNT. Comparison measurements with the Provisional Low Temperature Scale PLTS-2000 will be presented.