The W-band LEKID array of the MISTRAL instrument

The MISTRAL instrument is a cryogenic, W-band camera consisting of 415 lumped element kinetic inductance detectors. In a significant milestone achieved in May 2023, MISTRAL was successfully installed at the Gregorian focus of the Sardinia Radio Telescope, a 64 m aperture telescope in Italy. MISTRAL has a focal plane of ∼ 94 mm in diameter, resulting in an instantaneous field of view ∼ 4 arcmin. To preserve the high angular resolution of the telescope, which is ∼ 12 arcsec, the focal plane sampling has been tuned to 4.2 mm, corresponding to a pixel separation of ∼ 10.6arcsec. The remarkable combination of high angular resolution and wide instantaneous field of view makes MISTRAL an exceptionally versatile tool for continuum surveys of wide areas of the sky. Its unique capabilities significantly enhance the observational capacity of the Sardinia Radio Telescope. The lumped element kinetic inductance detectors of MISTRAL are obtained from a titanium-aluminum bilayer 10 + 30 nm thick on a single 100 mm–diameter Silicon wafer with thickness 235 μm. They exhibit a critical temperature of 945 mK and are optimized to operate within the temperature range of 200 to 240 mK. The feedline is made of an aluminum 21 nm thick and has a critical temperature of 1.35 K. We discuss the design, electrical, and optical characterization of the detector array, placing specific emphasis on the yield, the pixel identification on the array, the optical performance, and the calibration procedures.