The Instrument

The instrument was designed to measure the angular spectrum of the CMB anisotropy between l's of approximately 40 and 600 and between frequencies of 26 and 150 GHz. In addition to the following, information is also on the QMAP webpage.

Measuring this range of l-space should enable us determine whether there is a peak in the angular spectrum. Additionally, the highest frequency channels should be relatively immune from contamination by extra-galactic sources and galactic foreground emission.

The angular resolution and frequency coverage were chosen to overlap and complement those of the MAP satellite. In addition to channels at 30 and 40 GHz, which overlap the MAP frequencies, MAT has a 144 GHz channel with a 0.2 degree FWHM beam. At this angular scale MAP observes at 100 GHz. In addition to their intrinsic merit, TOCO's high frequency data will be useful in constraining sources of contamination in the MAP data set.

Here's a telescope sideview with scientists and truck. The QMAP gondola had been mounted on a Nike Ajax trailer (donation from Lucent Technologies). The building in the background is part of an abandoned sulpher mine. The compressor for the fridge is mounted on the back of the trailer and a 50 kW (at sea level) generator is off to the right. At altitude, the generator is rated to 30 kW.

Receiver

The receiver is comprised of both HEMT and SIS systems, which were developed by NRAO's electronic development facility in Charlottesville, Virginia. Both HEMTs and SIS detectors are cooled with a Sumitomo Model SRDK-408BA mechanical refrigerator. This model worked at the site without modification.

HEMT Channels: There are two Ka-band channels between 26 and 36 GHz, operated at 36 K. They observe the same pixel on the sky in two orthogonal polarizations. There are four Q-band channels operating in a single band between 36 and 46 GHz, operated at 36 K. They observe two orthogonal polarizations at each of two independent pixels on the sky. The HEMT amplifiers were designed by Marian Pospieszalski.

SIS Channels: There are two SIS mixers, one with a beam of roughly 0.2 degrees and the other with a beam of 0.3 degrees, both operated at 4 K. One of the amplifiers for the 1997 observing season was loaned to us by Ray Blundell. The SIS mixers were designed by A. Kerr and S.-K. Pan at NRAO.

Optics

The optics are comprised of an array of corrugated feed horns illuminating an off-axis parabola of diameter 85 cm. The edge taper of the parabola is about -25 dB. The parabola in turn under-illuminates a large chopping plate that sweeps the beam across the sky. It is essentially the same system used for the Saskatoon experiment, except that an array of detectors is supported. For details see Wollack et al.

• Beam patterns (units are degrees)
• Beam parameters