Cool science below 100 mK at 5140 meters elevation! Dilution refrigerator for Atacama Cosmology Telescope
JanisULT is proud to announce that it has developed, in collaboration with multi-agency scientific collaboration team called ACTPol, a new pulse-tube cooled cryogenic platform for the Atacama Cosmology Telescope (ACT). The ACT is a six-meter Gregorian telescope located at an altitude of 5,200 meters (17,000 ft) on Cerro Toco, in Northern Chile, and is dedicated to studies of the structure and evolution of the early universe through direct observation of the Cosmic Microwave Background (CMB) radiation at different polarizations and with arcminute resolution. Its new focal plane contains 3000 polarization-sensitive transition edge senor (TES) bolometers, which must be cooled to below 100 mK to work. The new platform, together with new optical tubes and detectors developed by ACTPol collaboration, constitutes the telescope “light receiver” (camera). When fully deployed, its three light-sensing detector packages, as well as parts of the optical system, will be cooled by an integrated cryogen-free 3He – 4He dilution refrigerator developed by JanisULT. During its first season of operation in 2013, the first 150 GHz detector package array (PA1) was successfully tested on site and first light was received with detectors below 100 mK, which made this experiment the only CMB experiment to operate at such a low temperature.
The Receiver temperature-controlled cabin is attached to the telescope primary-secondary mirror superstructure, and is moving together with the telescope during the scans.
The dilution refrigerator (DR), installed inside of the receiver, is remotely operated via Ethernet link and can move with acceleration of 1 G both vertically in the scan range of +/- 35 degree from neutral position, as well as horizontally. The air cooling system for electronics and pumps allows continuous operation at low atmospheric pressure of 500 mbar.
The receiver schematic is designed as a vacuum chamber with 50 K and 4 K shields on G-10 isolating supports, cooled by a dedicated Cryomech pulse-tube (PT) cryo-cooler PT-415 seen in the left lower corner.
The PT as well as dilution core are installed tilted to the optical central axis to allow DR operation in full scan range.
The test results both as is and integrated with the receiver have shown that it is fully compliant with technical specification set up by the ACTPol collaboration. Employing the highly-customized remotely controlled liquid-cryogen-free dilution refrigerator, without thermal cycling of commonly used single-shot adiabatic demagnetization refrigerator (ADR) cooling systems, significantly improved enabled day-time scanning strategies. Base temperature well below the target of 100 mK and cooling power of 120 µW@100mK was achieved with air cooled HighPace 300 Turbo and Edwards XDS35 scroll pumps.
In Spring 2013, the first 150 GHz kilo-TES polarimeters array package (PA1) was deployed for operation in the ACTPol receiver on the ACT site. In early 2014, a second 150 GHz array package (PA2), and a multichroic 90/150 GHz array package (PA3) will be deployed for a complete focal plane across three optics tubes.
As of June 2013, the ACTPol receiver has been successfully shipped to and integrated on the ACT site in Chile. First light and commencement of season one operations (PA1) was in July 2013.
Operations with full focal-plane deployment are projected for Spring 2014.
See product detail here