Comparison of low noise cooling performance of a Joule-Thomson cooler and a pulse-tube cooler using a HT SQUID

Abstract

Due to their intrinsic low mechanical vibration level both, Joule-Thomson refrigerator and Pulse-Tube refrigerator are promising candidates for low noise cooling of high-Tc SQUIDs. We report here on a test comparing the performance of a commercial Joule-Thomson cooler and a single stage Pulse-Tube cooler used to operate one and the same HT rf SQUID under comparable conditions in shielded environment. In order to reduce vibrations the cold stages of both cooler systems were connected by flexible plastic lines of several meters length with their compressors. Operated in a liquid nitrogen cryostat, the white field noise of the SQUID was 40jT,/&z at frequencies above 30 Hz. A slightly higher white noise (about 6OfT/&z) was observed for operation with either of the two coolers. This is probably due to the vicinity of superinsulation to the SQUID. The Joule-Thomson cooler produced a somewhat higher low frequency excess noise below 30 Hz and some characteristic noise bands at intermediate frequencies (ca. 100 Hz -500 Hz). The Pulse-Tube cooler led to a spectrum of lines at multiples of the pulse frequency (4.6 Hz). Both effects could be attributed (using cross correlation measurements) to residual mechanical vibrations of the cold heads of both coolers.

Application Fields of High-Temperature Superconductors

“…Joule-Thomson ("JT") coolers are based on the heat exchange during the expansion of a continuous gas flow. A commercial JT cooler with a cooling power of 3 W @ 77 K has been used successfully for HTS SQUID cooling [102].…”

“…Stirling-type PT with a cooling power of 12 W @ 80 K are commercially available where only the compressor requires servicing every 20 000 h. Miniature PT are in use for 10 year long-life space applications [109]. PT coolers were used with success for the cooling of HTS SQUID and rf devices [102,111]. A completely non-metallic PT cooler has been tested with success for low magnetic noise SQUID cooling [111].…”

A cryogenic 14‐channel 13C receiver array for 3T human head imaging

“… 25 More sophisticated designs have coils mounted on heat‐conductive substrates like sapphire 26 and alumina, 14 , 27 which are put in direct contact with liquid 20 or gas 10 , 28 , 29 coolants. Closed‐cycle coolers like Gifford‐McMahon refrigerators, 30 Joule‐Thomson machines, 31 , 32 and pulse‐tube coolers 31 , 33 can also be used to cool coils, even cryogen‐free. 32 , 33 …”

Electronic Axial HTS dc SQUID Gradiometer Cooled by Pulse-Tube Cooler

“…For a SQUID system cooled by a cryocooler, there are three main problems that should be addressed: electromagnetic interference (EMI), mechanical vibration and temperature fluctuations. Joule-Thomson and pulse-tube coolers are often used for high-SQUID operation due to their intrinsic low level of EMI and mechanical vibration in the cold stages [1]- [3].…”