Status of the POLARBEAR-2a CMB Telescope

The Simons Array consists of 3 telescopes (POLARBEAR-2a, -2b, and -2c) designed to observe the Cosmic Microwave Background at frequencies between 75 and 300 GHz from an altitude of 5190 m atop the Chajnantor Plateau in the Chilean Atacama desert. Each telescope is an off-axis Gregorian designed to be sensitive to a large dynamic range of angular scales on the sky, enabling the study of both the lensing and the potential primordial B-mode polarization signals. Three cryogenic lenses and an aperture stop image a 4.5 degree field of view onto each focal plane, and continuously rotating half-wave plates modulate the polarization signal to mitigate sensitivity degradation at large angular scales. The Simons Array will contain 5691 dichroic polarization-sensitive lenslet-coupled planar antennas, each connected to four transition-edge sensor bolometers, cooled to operating temperatures below 300 mK. The detectors are read out with frequency-division multiplexing electronics operating in the 1.5 to 4.5 MHz band with a multiplexing factor of 40. POLARBEAR-2a, which has observation bands centered at 90 and 150 GHz, was deployed and achieved first light in December 2018. In this talk, I will present the current status of POLARBEAR-2a and summarize its initial on-sky performance.