The Optical Design of the Background Emission Anisotropy Scanning Telescope (BEAST)

Abstract

We present the optical design of the Background Emission Anisotropy Scanning Telescope (BEAST), an off-axis Gregorian telescope designed to measure the angular distribution of the cosmic microwave background radiation (CMBR) at 30 and 41.5 GHz on angular scales ranging from 20' to 10 degrees. The aperture of the telescope is 1.9 m, and our design meets the strict requirements imposed by the scientific goals of the mission: the beam size is 200 at 41.5 GHz and 260 at 30 GHz, while the illumination at the edge of the mirrors is lower than -30 dB for the central horn. The primary mirror is an off-axis section of a paraboloid, and the secondary an off-axis section of an ellipsoid. A spinning flat mirror located between the sky and the primary provides a two-dimensional chop by rotating the beams around an ellipse on the sky. BEAST uses a receiver array of cryogenic low noise InP High Electron Mobility Transistor (HEMT) amplifiers. The baseline array has seven horns matched to one amplifier each and one horn matched to two amplifiers (two polarizations) for a total of nine amplifiers. Two horns operate around 30 GHz, and six operate around 41.5 GHz. Subsequent campaigns will include 90 GHz and higher frequency channels

Angular power spectrum of the fastica cosmic microwave background component from Background Emission Anisotropy Scanning Telescope data

“…The BEAST is a 2.2-m off-axis Gregorian telescope (Figueiredo et al 2005) with a focal plane consisting of six Q band (38-45 GHz) and two Ka band (26-36 GHz) corrugated scalar feed horns coupled with cryogenic High Electron Mobility Transistor (HEMT) amplifiers (Childers et al 2005). The instrument was installed at the UC White Mountain Research Station at an altitude of 3.8 km in 2001 July.…”

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

“…The WMPol telescope is an off-axis Gregorian telescope with a 2.2-meter diameter parabolic primary. The telescope design, which obeys the Dragone-Mizugutch condition (Dragone 1978;Mizugutch, Akagawa, & Yokoi 1976), is similar to that of BEAST, a telescope dedicated to mapping CMB temperature anisotropies (Childers et al 2005;Figueiredo et al 2005;Meinhold et al 2005;Mejía et al 2005;O'Dwyer et al 2005;Donzelli et al 2006), and uses identical aluminum coated carbon fiber reflectors. Figure 1 shows the optical design including the primary, 0.9-meter diameter ellipsoidal secondary, and the dewar that houses the receivers.…”