Alan R. Levy

Compass: An upper limit on cosmic microwave background polarization at an angular scale of 20'

COMPASS is an on-axis 2.6 meter telescope coupled to a correlation polarimeter operating at a wavelength of 1 cm. The entire instrument was built specifically for CMB polarization studies. We report here on observations of February 2001 - April 2001 using this system. We set an upper limit on E-mode polarized anisotropies of 33.5 uK (95% confidence limit) in the l-range 200-600.COMPASS is an on-axis 2.6 m telescope coupled to a correlation polarimeter operating at a wavelength of 1 cm. The entire instrument was built specifically for cosmic microwave background (CMB) polarization studies. We report here on observations of 2001 February-April using this system. We set an upper limit on E-mode polarized anisotropies of 1036 μK2 (95% confidence limit) in the l range 93-555.

THE BACKGROUND EMISSION ANISOTROPY SCANNING TELESCOPE (BEAST) INSTRUMENT DESCRIPTION AND PERFORMANCES

The Background Emission Anisotropy Scanning Telescope (BEAST) is a millimeter wavelength experiment designed to generate maps offluctuations inthecosmicmicrowave background (CMB). The telescope is composed of an off-axis Gregorian optical systemwith a 2.2 mprimary thatfocuses the collected microwave radiation onto an array of cryogenically cooled high electron mobility transistor (HEMT) receivers. This array is composed of six corrugated scalar feed horns in the Q band (38 to 45 GHz) and two more in the Ka band (26 to 36 GHz) with one of the six Q-band horns connected to an ortho-mode transducer for extraction of both polarizations incident on the

Continuous and Periodic Sorption Cryocoolers for 10 K and Below

This paper presents the current status of both continuous and periodic operation sorption cryocooler development for astrophysics missions requiring refrigeration to 10 K and below. These coolers are uniquely suited for cooling detectors in planned astrophysics missions such as the Exploration of Neighboring Planetary Systems, the Next Generation Space Telescope, and Darwin. The cooler requirements imposed by these missions include ten year life and the ability to scale designs to provide only a few milliwatts of refrigeration while consuming only a few watts of input power. In addition, the ExNPS and Darwin missions add stringent requirements for zero-vibration and zero EMI/EMC operation.

A 31 pixel flared 100-GHz high-gain scalar corrugated nonbonded platelet antenna array

A compact 100-GHz corrugated platelet antenna array has been developed based on a corrugated feed design for the background emission anisotropy scanning telescope (BEAST) optics. The antennas in the array result in a gain of 20 dB, and a bandwidth across the full range of W-band 75-110 GHz. The side lobes are down by about -25 dB, a requirement comparable to feed horns used for observation of the cosmic microwave background. The design and fabrication presented in this letter is straightforward and inexpensive. A feature is that because the plates are not permanently bonded, the horn can be disassembled and modified to change its properties such as addition of flare plates or modified rib structures.

The White Mountain Polarimeter Telescope and an Upper Limit on Cosmic Microwave Background Polarization

The White Mountain Polarimeter (WMPol) is a dedicated ground-based microwave telescope and receiver system for observing polarization of the cosmic microwave background. WMPol is located at an altitude of 3880 m on a plateau in the White Mountains of Eastern California, at the Barcroft Facility of the University of California White Mountain ResearchStation.Presentedhereisadescriptionof theinstrumentandthedatacollectedduring2004AprilthroughOctober. We set an upper limit on E-mode polarization of 14� K (95% confidence limit) in the multipole range 170 < l < 240. This result was obtained with 422 hr of observations of a 3 deg 2 sky area about the North Celestial Pole, using a 42 GHz

A Spin-Modulated Telescope to Make Two-Dimensional Cosmic Microwave Background Maps

We describe the HEMT Advanced Cosmic Microwave Explorer (HACME), a balloon-borne experiment designed to measure subdegree-scale cosmic microwave background anisotropy over hundreds of deg2, using a unique two-dimensional scanning strategy. A spinning flat mirror that is canted relative to its spin axis modulates the direction of beam response in a nearly elliptical path on the sky. The experiment was successfully flown in 1996 February, achieving near laboratory performance for several hours at float altitude. A map free of instrumental systematic effects is produced for a 3.5 hr observation of 630 deg2, resulting in a flat-band power upper limit of l(l + 1)Cl/(2π)0.5 < 77 μK at l = 38 (95% confidence). The experiment design, flight operations, and data, including atmospheric effects and noise performance, are discussed.

COMPASS: an instrument for measuring the polarization of the CMB on intermediate angular scales

Abstract COMPASS is an on-axis 2.6-m telescope coupled to a correlation polarimeter. The entire instrument was built specifically for CMB polarization studies. Careful attention was given to receiver and optics design, stability of the pointing platform, avoidance of systematic offsets, and development of data analysis techniques. Here we describe the experiment, its strengths and weaknesses, and the various things we have learned that may benefit future efforts to measure the polarization of the CMB.

Characterization of Porous Metal Flow Restrictors for Use as the J-T Expander in Hydrogen Sorption Cryocoolers

A program has been completed to measure the flow rate of hydrogen at pressures up to 10 MPa through commercially manufactured porous metal flow restrictors. Such flow restrictors offer substantially greater resistance to contamination induced plugging or changes in flow when compared with conventional orifices and capillary tubing.

Performance Test Results for a 25 K Sorption Cryocooler Designed for the UCSB Long Duration Balloon Cosmic Microwave Background Radiation Experiment

A continuous operation, vibration-free, long-life 25 K sorption cryocooler has been built and is now in final integration and performance testing. This cooler will be flown on the University of California at Santa Barbara Long Duration Balloon Cosmic Microwave Background Radiation experiment in Antarctica in December 1997. The cooler will refrigerate a focal plane composed of eight microwave feed horns, two working at 30 GHz and six at 42 GHz, with InP High Electron Mobility Transistor amplifiers. This will be the first hydride sorption cooler used to support an astrophysics experiment. As such, it is an important milestone in the development of vibration-free coolers for astrophysics applications.

Imaging the cosmic microwave background: The BEAST experiment

We describe the Santa Barbara BEAST experiment, a balloon borne telescope to image the Cosmic Microwave Background (CMB) radiation anisotropy pattern. Some aspects of the map making pipeline are also discussed.