The CUORE Pulse Tube Noise Cancellation Technique

Abstract

The 1-ton-scale CUORE detector is made of 988 ${{{\hbox {TeO}}}}_2$ crystals operated as cryogenic bolometers at a working temperature of $\sim 10{{{\hbox { mK}}}}$. In order to provide the necessary cooling power at 4 K stage, a total of five pulse tube (PT) refrigerators are used. The PTs make the cryogenic system reliable and stable, but have the downside that mechanical vibrations at low frequencies (1.4 Hz and related harmonics) are injected into the experimental apparatus. An active noise cancellation technique has been developed in order to reduce such effect by taking advantage from the coherent interference of the pressure oscillations originated by the different PTs. The technique that will be presented consists in controlling the relative phases of the pressure waves running inside the CUORE PT lines, in order to achieve the lowest detector noise. By reducing the power of PT harmonics by a factor up to $10^4$, it drastically suppresses the overall noise RMS on the CUORE detector. In the following, we demonstrate the reliability and effectiveness of the technique, showing that the optimization of the detector noise level is possible in different experimental conditions.