Takahiro Okamura

The POLARBEAR Experiment

We present the design and characterization of the POLARBEAR experiment. POLARBEAR will measure the polarization of the cosmic microwave background (CMB) on angular scales ranging from the experiment’s 3.5’ beam size to several degrees. The experiment utilizes a unique focal plane of 1,274 antenna-coupled, polarization sensitive TES bolometers cooled to 250 milliKelvin. Employing this focal plane along with stringent control over systematic errors, POLARBEAR has the sensitivity to detect the expected small scale B-mode signal due to gravitational lensing and search for the large scale B-mode signal from inflationary gravitational waves. POLARBEAR was assembled for an engineering run in the Inyo Mountains of California in 2010 and was deployed in late 2011 to the Atacama Desert in Chile. An overview of the instrument is presented along with characterization results from observations in Chile.

POLARBEAR constraints on cosmic birefringence and primordial magnetic fields

Author(s): Ade, PAR; Arnold, K; Atlas, M; Baccigalupi, C; Barron, D; Boettger, D; Borrill, J; Chapman, S; Chinone, Y; Cukierman, A; Dobbs, M; Ducout, A; Dunner, R; Elleflot, T; Errard, J; Fabbian, G; Feeney, S; Feng, C; Gilbert, A; Goeckner-Wald, N; Groh, J; Hall, G; Halverson, NW; Hasegawa, M; Hattori, K; Hazumi, M; Hill, C; Holzapfel, WL; Hori, Y; Howe, L; Inoue, Y; Jaehnig, GC; Jaffe, AH; Jeong, O; Katayama, N; Kaufman, JP; Keating, B; Kermish, Z; Keskitalo, R; Kisner, T; Kusaka, A; Le Jeune, M; Lee, AT; Leitch, EM; Leon, D; Li, Y; Linder, E; Lowry, L; Matsuda, F; Matsumura, T; Miller, N; Montgomery, J; Myers, MJ; Navaroli, M; Nishino, H; Okamura, T; Paar, H; Peloton, J; Pogosian, L; Poletti, D; Puglisi, G; Raum, C; Rebeiz, G; Reichardt, CL; Richards, PL; Ross, C; Rotermund, KM; Schenck, DE; Sherwin, BD; Shimon, M; Shirley, I; Siritanasak, P; Smecher, G; Stebor, N; Steinbach, B; Suzuki, A; Suzuki, JI; Tajima, O; Takakura, S; Tikhomirov, A; Tomaru, T; Whitehorn, N; Wilson, B; Yadav, A; Zahn, A | Abstract:

The Simons Array: expanding POLARBEAR to three multi-chroic telescopes

The Simons Array is an expansion of the POLARBEAR cosmic microwave background (CMB) polarization experiment currently observing from the Atacama Desert in Northern Chile. This expansion will create an array of three 3.5m telescopes each coupled to a multichroic bolometric receiver. The Simons Array will have the sensitivity to produce a ≥ 5σ detection of inationary gravitational waves with a tensor-to-scalar ratio r ≥ 0:01, detect the known minimum 58 meV sum of the neutrino masses with 3σ confidence when combined with a next-generation baryon acoustic oscillation measurement, and make a lensing map of large-scale structure over the 80% of the sky available from its Chilean site. These goals require high sensitivity and the ability to extract the CMB signal from contaminating astrophysical foregrounds; these requirements are met by coupling the three high-throughput telescopes to novel multichroic lenslet-coupled pixels each measuring CMB photons in both linear polarization states over multiple spectral bands. We present the status of this instrument already under construction, and an analysis of its capabilities.

Cryogenic infrared filter made of alumina for use at millimeter wavelength

We propose a high-thermal-conductivity infrared filter using alumina for millimeter-wave detection systems. We constructed a prototype two-layer antireflection-coated alumina filter with a diameter of 100 mm and a thickness of 2 mm and characterized its thermal and optical properties. The transmittance of this filter at 95 and 150 GHz is 97% and 95%, respectively, while the estimated 3 dB cut-off frequency is at 450 GHz. The high thermal conductivity of alumina minimizes thermal gradients. We measure a differential temperature of only 0.21 K between the center and the edge of the filter when it is mounted on a thermal anchor of 77 K. We also constructed a thermal model based on the prototype filter and analyzed the scalability of the filter diameter. We conclude that the temperature increase at the center of the alumina IR filter is less than 6 K, even with a large diameter of 500 mm, when the temperature at the edge of the filter is 50 K. This is suitable for an application to a large-throughput next-generation cosmic-microwave-background polarization experiment such as POLARBEAR-2.

Construction of Superconducting Magnet System for the J-PARC Neutrino Beam Line

Following success of a prototype R&D, construction of a superconducting magnet system for J-PARC neutrino beam line has been carried out since 2005. A new conceptual beam line with the superconducting combined function magnets demonstrated the successful beam transport to the neutrino production target.

Test Results of Superconducting Combined Function Prototype Magnets for the J-PARC Neutrino Beam Line

Superconducting combined function magnets are adopted for the 50 GeV, 750 kW proton beam line for the J-PARC neutrino experiment, and two full-scale prototype magnets have been developed successfully at KEK. In the cold tests, both prototypes were excited up to 7700 A without spontaneous quenches. The measured field quality of the both prototypes agreed well with the design field, indicating that the fabrication process has no major problem. The heater quench tests of the first prototype, however, showed that the magnet was not self-protected. Consequently, the design was revised and quench protection heaters were adopted. In quench heater tests of the second prototype magnet using small sheet heaters, the fundamental characteristics of the quench protection heaters were studiedSuperconducting combined function magnets for the J-PARC (Japan Proton Accelerator Research Complex) neutrino experiment have been successfully developed at High Energy Accelerator Research Organization, KEK. The first prototype magnet reassembled for the quench protection studies, and the cold test result indicated that the eight quench protection heaters are effective for the safe protection of the magnet. Three production magnets have been fabricated and tested at 4.5 K, 1 atm, in a vertical cryostat, and the excellent excitation and quench performances are observed. In the field measurement during cold tests, all the magnets indicated the field qualities good enough to fulfill the specification. The field measurement at room temperature has been also performed with the three production magnets for checking the dipole field component. The results are consistent with the computation.

Commissioning Results of Superconducting Magnet System for the Neutrino Beam Line

The first commissioning of a magnet system for the neutrino beam line in the J-PARC has been performed from January to March, 2009. The magnet system could be cooled down successfully in 9 days. RRRs of all the magnets and joint resistances in the magnet string were measured to be reasonable values. The magnet string composed of 28 superconducting combined function magnets could be excited up to 5000 A after several shutdown tests without a spontaneous quench. A quench protection scheme with a magnet safety system developed by CEA/SACLAY were verified to work properly. As for beam commissioning, the proton beams could pass through the arc section including the superconducting magnet string on the first attempt, and the magnet protection system were verified to work quite well even in a beam induced quench test.

Status of Superconducting Magnet System for the J-PARC Neutrino Beam Line

A superconducting magnet system for the J-PARC neutrino beam line has been under construction since 2004. The system consists of 14 doublet cryostats; each contains 2 combined function magnets (SCFM). The SCFM uses two single layer left/right asymmetric coils that produce a dipole field of 2.6 T and quadrupole of 19 T/m. The SCFMs had been developed by 2004, mass-produced since 2005, and completed by summer 2008. The system is being installed since Feb. 2008 till the end of 2008. The paper summarizes the system overview including cryogenics and safety peripheries. The paper also reports the production and installation status.

Status of Superconducting Solenoid System for COMET Phase-I Experiment at J-PARC

The COMET Phase-I experiment now under construction at the Hadron Hall of J-PARC aims to search for coherent neutrinoless conversion of a muon to an electron. The experiment requires a large superconducting solenoid system that consists of 5-T pion capture solenoid and 5~3 T matching solenoid and 3-T 90° pion decay/muon transport curved solenoid. The capture solenoid encloses a target to generate pions. The neutron irradiation generated by the target causes various influences to the capture solenoid. One of the major issues is the cooling of the coil that can be degraded due to irradiation. The analyses and the design that accommodate the irradiation were performed. This paper summarizes the concept of the COMET Phase-I experiment and also the design of the solenoid system, including the analyses associated with the neutron irradiation. Manufacturing of the solenoid system has already started, and its status is also reported in this paper.

POLARBEAR-2 optical and polarimeter designs

POLARBEAR-2 is a ground based cosmic microwave background (CMB) radiation experiment observing from Atacama, Chile. The science goals of POLARBEAR-2 are to measure the CMB polarization signals originating from the inflationary gravity-wave background and weak gravitational lensing. In order to achieve these science goals, POLARBEAR-2 employs 7588 polarization sensitive transition edge sensor bolometers at observing fre quencies of 95 and 150 GHz with 5.5 and 3.5 arcmin beam width, respectively. The telescope is the off-axis Gregorian, Huan Tran Telescope, on which the POLARBEAR-1 receiver is currently mounted. The polarimetry is based on modulation of the polarized signal using a rotating half-wave plate and the rotation of the sky. We present the developments of the optical and polarimeter designs including the cryogenically cooled refractive optics that achieve the overall 4 degrees field-of-view, the thermal filter design, the broadband anti-reflection coating, and the rotating half-wave plate.