GroundBIRD is an experiment to observe the cosmic microwave background at 145 and 220GHz. It aims to observe the B-mode polarisation signal from inflation in the early universe. It is located at Teide Observatory, on the island of Tenerife in the Canary Islands.
 GroundBIRD in 2019 | |
| Part of | Teide Observatory  |
|---|---|
| Location(s) | Tenerife, Atlantic Ocean, international waters |
| Coordinates | 28°18′02″N 16°30′37″W / 28.30042°N 16.51028°W |
| Altitude | 2,400 m (7,900 ft) |
| Wavelength | 145, 220 GHz (2.07, 1.36 mm) |
| Telescope style | cosmic microwave background experiment radio telescope |
| Diameter | 30 cm (1 ft 0 in) |
| Angular resolution | 0.5 degree, 0.3 degree |
  Location of GroundBIRD | |
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Scientific goals
The telescope was constructed to measure the B-mode signal in the polarisation of the Cosmic Microwave Background (CMB),[1] in order to look for evidence of cosmic inflation in the early universe. It aims to observe the reionization bump at 
Telescope
The telescope consists of two mirrors in a Mizuguchi-Dragone configuration, with a diameter of 30 cm (12 in). The telescope is inside the cryostat, which is mounted on a rotation table, with a rotary joint that provides helium gas and electricity to the cryostat.[2][3] The mirrors are cooled to 4 K (−269.15 °C) using a Pulse tube refrigerator to reduce the thermal noise from the mirror surfaces.[2]
The experiment uses microwave kinetic inductance detectors (MKIDs),[4] which are cooled to 250mK by a sorption cooler within the cryostat, which uses helium-3, and was manufactured by Chase Research Cryogenics Ltd.[2] The signals from the detector are multiplexed, and around 100 detectors can be measured in both phase and amplitude with a single digital read-out system with a bandwidth of 200MHz, recording 1,000 samples per second. The digital system uses 12-bit ADCs and a Kintex-7 FPGA from Xilinx initially,[4] and now uses Kintex ultrascale FPGAs.[citation needed] Raspberry Pis are used to monitor and control the telescope.[5]
The cryostat rotates at 20 rpm (120° per second, 1 rotation every 3 seconds) to minimize 1/f noise.[2][6][7] It observes at zenith angles up to 20°, mapping around 40% of the sky. The field of view is 10°, with an angular resolution of 0.5° FWHM at 145GHz, and 0.3° at 220GHz.[2] It will measure the CMB at 
The telescope was constructed at KEK in Japan.[2] Test observations started in Japan in 2014. While it was originally intended that it would observe from the Atacama Desert in Chile,[6] an agreement to install it at Teide Observatory was reached in 2016,[8][1][9] at an altitude of 2,400 metres (7,900 ft).[2][10] It was shipped to Tenerife in January 2019.[7] In February 2020, the experiment was visited by Kenji Hiramatsu, the Japanese Ambassador to Spain.[11]
Collaboration
The collaboration includes scientists from:
- Delft University of Technology, Netherlands[2]
- The Graduate University for Advanced Studies, Japan[4]
- Korea Astronomy and Space Science Institute, Korea[2][12]
- Instituto de Astrofísica de Canarias, Canary Islands, Spain[2]
- KEK, Japan[2]
- Korea University, Korea[2]
- Kyoto University, Japan[2]
- National Astronomical Observatory of Japan, Japan[2]
- RIKEN, Japan[2]
- Saitama University, Japan[2]
- Tohoku University, Japan[2]
- University of Tokyo, Japan[2]
Funding
The project is funded by:
- Ministry of Education, Culture, Sports, Science and Technology, Japan[4][6]
- The Graduate University for Advanced Studies, Japan[6]
- National Astronomical Observatory of Japan, Japan[6]
- National Research Foundation of Korea, Korea[6]
with additional support from: