AMKID: A large KID-based camera at the APEX telescope

Thermal emission at submillimeter wavelengths carries unique information for many astronomical applications, ranging from disks and planet formation around young stars to galaxy evolution studies at cosmological distances. Advancing the mapping speed to detect this faint emission in ground-based astronomy has been a technical challenge for decades. The APEX Microwave Kinetic Inductance Detector (AMKID) camera was designed to accomplish this task. The instrument is a wide field-of-view camera based on kinetic inductance detectors. It is installed on the 12-meter APEX telescope in Chile at 5.100 meters above sea level. The instrument operates in dual color, covering the 350 GHz and 850 GHz atmospheric windows simultaneously. It has a large field of view of 15.3' x 15.3' and an unprecedented number of pixels: 13.952 detectors in the high-frequency band and 3.520 detectors in the low-frequency band. Here we present a complete description of the instrument design and construction, together with results from the successful low-frequency-array (LFA) commissioning campaign executed over the last year. The LFA performance is in good agreement with design parameters, with detector sensitivity of 2.2 mK and diffraction-limited beam sizes of 17.0''. On-sky measurements demonstrate a sensitivity of 70-90 mJy per detector under good atmospheric conditions (PWV below 1.0mm). With this performance the LFA regularly achieves a mapping sensitivity of 25 mJy when mapping a square degree in one hour. AMKID on APEX with its dual-color observing capabilities, high sensitivity, large field of view, and high angular resolution promises to open new scientific opportunities with the APEX telescope.