GroundBIRD is a ground-based cosmic microwave background (CMB) experiment for observing the polarization pattern imprinted on large angular scales (ℓ > 6 ) from the Teide Observatory in Tenerife, Spain. Our primary scientific objective is a precise measurement of the optical depth τ (σ(τ ) ∼ 0.01) to the reionization epoch of the Universe to cross-check systematic effects in the measurements made by previous experiments. GroundBIRD observes a wide sky area in the Northern Hemisphere (∼ 40% of the full sky) while continuously rotating the telescope at a high speed of up to 20 rotations per minute (rpm) to overcome the fluctuations of atmospheric radiation. We have adopted the NbTiN/Al hybrid microwave kinetic inductance detectors (MKIDs) as focal plane detectors. We observe two frequency bands centered at 145 GHz and 220 GHz. The 145 GHz band picks up the peak frequency of the CMB spectrum. The 220 GHz band helps accurate removal of the contamination of thermal emission from the Galactic interstellar dust. The MKID arrays (138 MKIDs for 145GHz and 23 MKIDs for 220GHz) were designed and optimized so as to minimize the contamination of the two-level-system noise and maximize the sensitivity. The MKID arrays were successfully installed in May 2023 after the performance verification tests were performed at a laboratory. GroundBIRD has been upgraded to use the full MKID arrays, and scientific observations are now underway. The telescope is automated, so that all observations are performed remotely. Initial validations, including polarization response tests and observations of Jupiter and the moon, have been completed successfully. We are now running scientific observations.
SCUBA-2/POL-2 has been the most productive instrument at JCMT since it’s fully commissioned in 2011 September, and it’s constantly oversubscribed during the call-for-proposals by a factor of 3 to 5. The proposed new 850μm instrument will feature 7272 state-of-the-art Microwave Kinetic Inductance Detectors (MKIDs) operated below 100 mK, fully utilizing the JCMT’s 12 arcmin Field of View (FoV), thus have all the capabilities of SCUBA-2 at 850 μm, yet will map an order of magnitude faster. The new instrument will be incorporated with intrinsic polarization measurement capability which is 3636 pixels. Mapping the 850 μm polarization will be improved by a factor of at least 20.
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