The detector system for the stratospheric kinetic inductance polarimeter (skip)

The stratospheric kinetic inductance polarimeter is a proposed balloon-borne experiment designed to study the cosmic microwave background, the cosmic infrared background and Galactic dust emission by observing 1,133 deg² of sky in the Northern Hemisphere with launches from Kiruna, Sweden. The instrument contains 2,317 single-polarization, horn-coupled, aluminum lumped-element kinetic inductance detectors (Lekids). The Lekids will be maintained at 100 mK with an adiabatic demagnetization refrigerator. The polarimeter operates in two configurations, one sensitive to a spectral band centered on 150 GHz and the other sensitive to 260 and 350 GHz bands. The detector readout system is based on the ROACH-1 board, and the detectors will be biased below 300 MHz. The detector array is fed by an F/2.4 crossed-Dragone telescope with a 500 mm aperture yielding a 15 arcmin FWHM beam at 150 GHz. To minimize detector loading and maximize sensitivity, the entire optical system will be cooled to 1 K. Linearly polarized sky signals will be modulated with a metal-mesh half-wave plate that is mounted at the telescope aperture and rotated by a superconducting magnetic bearing. The observation program consists of at least two, 5-day flights beginning with the 150 GHz observations.