Calibration System with Cryogenically-Cooled Loads for QUIET-II Detector

1. Calibration System with Cryogenically-Cooled Loads for QUIET-II Detector M. Hasegawa, O. Tajima, Y. Chinone, M. Hazumi, K. Ishidoshiro, M. Nagai High Energy Accelerator Research Organization, KEK 2. Detector and Characterization 1. QUIET Phase-II • QUIET Detector The Q/U Imaging Experiment (QUIET) is an experimental program to make very sensitive measurement of the Cosmic Microwave Background (CMB) polarization from the ground. The primary goal is to detect the degree-scale B-modes induced by primordial gravitational waves, which is a “smoking gun” signature of inflation. Having demonstrated our techniques in the first phase, we are preparing for the second phase of QUIET with ~500 detectors. One of new challenges towards QUIET Phase-II is to (precisely) characterize the large number of detectors in the laboratory, and the calibration system reported here is newly developed for that purpose. OMT QUIET employs a HEMT-based pseudo-correlation receiver. A large focal-plane detector array is realized by a breakthrough in millimeter-wave circuit technology and packaging at JPL. HEMT • Pseudo Correlation Detector • - Measure Q/U polarization simultaneously • - Stable against gain fluctuation • Modulation (Phase switching) • - 1/f noise is strongly suppressed. • - Cancel out fake pol. signals. 3cm • Characterization The following quantities should be characterized in order to convert detector time stream into polarization power spectra. - Detector responsivities (mK/mV) - Detector polarization angle - Instrumental fake polarization Well-characterized polarization signal is required. 4. System Components 3. Calibration System • Cryostat and cryocooler • Metal Mirror • All-in-one polarization source • - Blackbody emitters are cooled with a • cryocooler as the cold load (~10K) • - Radiation is polarized by reflecting off • a metal mirror • Use 3 different materials to vary the pol. Amplitude. • Rotate in the vacuum with rotary feed-through shaft. • Advantages • - Well-characterized polarization signal • Amplitude : • Direction : Parallel to the mirror surface • - Two temperature loads • Unpolarized response can be calibrated simultaneously • - Reproducing the observing condition (chilean sky load : ~10 K) • Cylindrical cryostat (D 540mm,H 500mm) • 2 stage GM cryocooler • - enable two temperature loads • - thermal loads is 18/7W on 1st/2nd stage in • normal operation. • Blackbody emitter array We employ Eccosorb CR-112 an iron-loaded epoxy as the material for the blackbody emitter. To minimize the surface reflection, loads are casted with pyramid-shape grooves on the front surface. The measured power coefficient is typically -30dB. This system allows us to calibrate all the necessary quantities to characterize the QUIET-II detector simultaneously under a load condition similar to the actual observation. Definitive test system for CMB polarization detector 6. Performance 5. Principle • Inherent polarization signal • Resistivity vs Signal • - Polarization signal • - Inherent pol. is signal at 0Ωcm • No inherent polarization signal. • Expected Response • Detector Response • Total Power • Two levels are seen as expected. • - 10K (upper) and 30K (lower) • Polarizaton • Clear sinusoidal curve • - Amplitude is as expected. 10K 30K • All the calibration parameters are extracted from the response with respect to the mirror rotation angle. • Responsivity (pol.) : Amplitude/P • Responsivity (power) : DVI / DTload • Polarization Angle • : Phase of the sinusoidal curve • Instrumental fake polarization • : DVQ,U / (RKDTload ) 6. Summary We have developed a polarization calibrator for QUIET-II detectors, and successfully demonstrated its use with an actual QUIET detector. This is the first demonstration “in the laboratory” for the modulation of the polarization signal with a load temperature, which is as low as those at the observing site.