9413935 Readhead This project supports the development and construction of a research instrument -- the Cosmic Background Imager (CBI) -- to study the cosmic microwave background radiation on angular scales from 2'-20' with sensitivity Trms/T = 2 x 10-6. The CBI is a four element interferometer operating at 28 GHz - 36 GHz. Each element has a complement of three primary reflectors, of sizes 0.75 m, 1.5 m and 3 m, which will be selected according to the angular scale to be imaged. The instrument operates on a 16 m x 16 m "optical bench" on which the elements can be placed in a wide variety of configurations. The intermediate frequency and local oscillator signals are distributed via optical fibres. The CBI will make images of the cosmic microwave background radiation and hence enable determination of the spectrum of mass fluctuations on scales of 2 x 1012 solar mass to 2 x 1015 solar mass. This will provide foundation for theories of the formation of structure in the universe, and could provide a link between quantum fluctuations in the very early universe and the largest structures known. In addition, the CBI will be capable of making observations of the Sunyaev-Zel'dovich effect in clusters of galaxies, and will allow us to carry out detailed studies of the hot gas in clusters when used in combination with high resolution X-ray observations. The CBI will also be a tool for the study of diffuse galactic foreground emission. ***
