Sorption-based vibration-free cooler for the METIS instrument on E-ELT

Abstract

METIS is the 'Mid-infrared ELT Imager and Spectrograph' for the European Extremely Large Telescope. This E-ELT instrument will cover the thermal/mid-infrared wavelength range from 3 to 14 μm and will require cryogenic cooling of detectors and optics. We present a vibration-free cooling technology for this instrument based on sorption coolers developed at the University of Twente in collaboration with Dutch Space. In the baseline design, the instrument has four temperature levels: N-band: detector at 8 K and optics at 25 K; L/M-band: detector at 40K and optics at 77 K. The latter temperature is established by a liquid nitrogen supply with adequate cooling power. The cooling powers required at the lower three levels are 0.4 W, 1.1 W, and 1.4 W, respectively. The cryogenic cooling technology that we propose uses a compressor based on the cyclic adsorption and desorption of a working gas on a sorber material such as activated carbon. Under desorption, a high pressure can be established. When expanding the high-pressure fluid over a flow restriction, cooling is obtained. The big advantage of this cooling technology is that, apart from passive valves, it contains no moving parts and, therefore, generates no vibrations. This, obviously, is highly attractive in sensitive, high-performance optical systems. A further advantage is the high temperature stability down to the mK level. In a Dutch national research program we aim to develop a cooler demonstrator for METIS. In the paper we will describe our cooler technology and discuss the developments towards the METIS cooler demonstrator.

Baseline design of a sorption-based Joule-Thomson cooler chain for the METIS instrument in the E-ELT

“…Therefore, it is wise to operate the helium stage at 70 K to keep the overall system more efficient. Based on such analysis, a conceptual design of the METIS cooler chain was determined [9], as shown in Fig. 3.…”

“…Based on the requirements discussed above, a system-level baseline design of the cooler chain is made. Some preliminary results of this design have been presented in previous conference papers [9][10][11]. However, we have corrected and improved the calculation model from time to time during the development resulting minor adaptations.…”

METIS: the mid-infrared E-ELT imager and spectrograph

“…We have been trying to find out whether astronomical instruments can be cooled without mechanical coolers, and sorption cooling may be a viable solution. Within the context of METIS, the University of Twente has been developing the required technology [28] in collaboration with Dutch Space. The compressors are based on the cyclic adsorption and desorption of a working gas on a sorber material (activated carbon).…”

Sorption-based vibration-free cooler for the METIS instrument on E-ELT

“…Based on our experience with sorption-based cooler, we designed a sorption JT cooler chain that meets the requirements of the METIS instrument [7]. As shown in FIGURE 1, this conceptual design consists of three stages thermally linked in parallel, to obtain cooling at 40 K by a neon, 25 K by a hydrogen and 8 K by a helium-based cooler stage.…”