Observations of the Sunyaev-Zel'dovich effect at high angular resolution towards the galaxy clusters A665, A2163 and CL0016+16

We report on the first observation of the Sunyaev-Zel'dovich effect with the Diabolo experiment at the IRAM 30 metre telescope. A significant brightness decrement is detected in the direction of three clusters (Abell 665, Abell 2163 and CL0016+16). With a 30 arcsecond beam and 3 arcminute beamthrow, this is the highest angular resolution observation to date of the SZ effect.Comment: 23 pages, 8 figures, 6 tables, accepted to New Astronom

Further Developments on a Vibration-Free Helium-Hydrogen Sorption Cooler

In our continuous effort on the development of a passively precooled two-stage 4.5 K / 14.5 K helium-hydrogen sorption cooler, a number of important development steps were made. Firstly, an improved high-density activated carbon was used for the fabrication of four new sorption cells. Tests with these new cells showed that because of increased efficiency, the required passive radiator area for this cooler reduced by a factor of 1.3. Secondly, it was shown that this cooler architecture can easily be used to reach lower (or higher) temperatures. Without hardware changes, the cold temperature was reduced from 4.5 K to 3.1 K. Thirdly, long-term experiments were carried out on the cooler. In two separate periods of two and four months of continuous operation, no change at all was observed in the cooler performance. Fourthly, clogging effects were analyzed that occurred after a 15 months storage period of the cooler at 300 K. We concluded that hydrogen diffusion out of the stainless steel components should be prevented. Finally, a design of an integrated compact cooler chain was presented, which consists of a 50 K Stirling cooler and the helium-hydrogen sorption cooler. This package may be used in the future to test the sorption cooler technology in a zero-gravity environment

ACBAR: The Arcminute Cosmology Bolometer Array Receiver

We describe the Arcminute Cosmology Bolometer Array Receiver (ACBAR); a multifrequency millimeter-wave receiver designed for observations of the Cosmic Microwave Background (CMB) and the Sunyaev-Zel'dovich effect in clusters of galaxies. The ACBAR focal plane consists of a 16-pixel, background-limited, 240 mK bolometer array that can be configured to observe simultaneously at 150, 220, 280, and 350 GHz. With 4-5' FWHM Gaussian beam sizes and a 3 degree azimuth chop, ACBAR is sensitive to a wide range of angular scales. ACBAR was installed on the 2 m Viper telescope at the South Pole in January 2001. We describe the design of the instrument and its performance during the 2001 and 2002 observing seasons.Comment: 59 pages, 16 figures -- updated to reflect version published in ApJ

The polatron: A millimeter-wave cosmic microwave background polarimeter for the OVRO 5.5 m telescope

We describe the development of a bolometric receiver designed to measure the arcminute-scale polarization of the cosmic microwave background (CMB). The Polatron will be mounted at the Cassegrain focus of the 5.5 m telescope at the Owens Valley Radio Observatory (OVRO). The receiver will measure both the Q and U Stokes parameters over a 20% pass-band centered near 100 GHz, with the input polarization signal modulated at ~0.6 Hz by a rotating, birefringent, quartz half-wave plate. In six months of observation we plan to observe ~400 2.5 arcminute pixels in a ring about the North Celestial Pole to a precision of ~6 \mu K/pixel in each of Q and U, adequate to unambiguously detect CMB polarization at levels predicted by current models

Optimization of the working fluid in a Joule-Thomson cold stage

Vibration-free miniature Joule–Thomson (JT) coolers are of interest for cooling a wide variety of devices, including low-noise amplifiers, semiconducting and superconducting electronics, and small optical detectors used in space applications. For cooling such devices, coolers are needed which have operating temperatures within a wide temperature range of 2–250 K. In this paper, the optimization of the working fluid in JT cold stages is described that operate at different temperatures within that range. For each temperature, the most suitable working fluid is selected on the basis of the coefficient of performance of the cold stage, which is defined as the ratio of the gross cooling power to the change in Gibbs free energy of the fluid during compression. In addition, a figure of merit of the heat exchange in the counter-flow heat exchanger is evaluated that depends only on the properties of the working fluid