Realization of an ultra-high precision temperature control in a cryogen-free cryostat

Abstract

Single-pressure refractive-index gas thermometry (SPRIGT) is a new type primary thermometry jointly developed by TIPC of CAS in China and LNE-Cnam in France. To realize a competitive uncertainty of 0.25 mK for the thermodynamic temperature measurement, a cryogen-free cryostat with high-stability better than 0.2 mK should be designed. This paper presented the first experimental results of temperature control for this cryostat. To realize this objective, multi-layer radiation shields combined with a thermal-resistance method were used to isolate the thermal-noise from surroundings. Besides, a new temperature control method based on a gas-type heat switch and proportional-integral-derivative control method was proposed, which was applicable to different temperature ranges by changing the working modes of the heat switch. After optimizing, the ultra-high precision temperature control in the range of 5–25 K has been fully realized, which was the temperature instability (with standard deviation) of 0.021 mK at 5.0 K, 0.05 mK at 5.7 K, 0.042 mK at 7.4 K, 0.029 mK at 14.3 K, and 0.022 mK at 25 K with the sampling time of 0.8 s. This was almost the best reporting result in the world and showed its great potential in SPRIGT.

Refractive-index gas thermometry

“…Disadvantages of SPRIGT include the need for a reference temperature, the absence of redundant data from multiple measuring pressures, and the requirement for careful design of the cryostat gas line tubing in order to allow low uncertainty estimation of the hydrostatic head correction at each temperature. The SPRIGT apparatus is comprised mainly of three sub-systems, namely the cryostat system cooled using a two-stage pulse-tube (Gao et al 2018, Chen et al 2019), the gas-handling system where pressure is maintained constant by a servo-loop (Han et al 2018) and the microwave system at the heart of which lies the quasi-spherical resonator (Zhang et al 2019).…”

Active suppression of temperature oscillation from a pulse-tube cryocooler in a cryogen-free cryostat: Part 2. Experimental realization

“…A cryogen-free cryostat cooled by a closed cycle cryocooler, such as a Gifford-McMahon (GM) or GM type pulse tube cryocooler (GM-PTC), can provide an uninterrupted long-term low temperature operating environment (from 3 K-300 K). Its intrinsic temperature oscillation, however, limits its application in experiments requiring high thermal stability at low temperature (especially below 77 K).Thus far, many researchers have made efforts to reduce this temperature oscillation, using the heat-capacity method [1][2][3][4][5][6][7], the thermal-resistance method [8][9][10] and the heat-switch method [11][12][13]. However, to the best of our knowledge, no one has yet used active suppression.…”

Acoustic measurement of the triple point of neon T Ne and thermodynamic calibration of a transfer standard for accurate cryogenic thermometry

“…When cooling began, a small amount of helium exchange gas (approximately 1000 Pa) was admitted into the sealed space between the shield designated 'heat switch' and the pressure vessel (figure 3). The lowest temperature reached by the pressure vessel was approximately 6 K. The methods for temperature control are the same ones that we used in previous work [7,[11][12][13]. Referring to figure 3, the finest temperature control of the quasisphere was achieved by reading cSPRT-1 with an F18 bridge and feeding the bridge's output through a proportional-integral feedback loop to heater-3.…”