SCUBA - Submillimetre common-user bolometer array for the James Clerk Maxwell telescope

A submillimeter continuum array instrument being built for the 15-m James Clerk Maxwell Telescope on Mauna Kea, Hawaii is described. The instrument contains 2 arrays, one of 91 pixels optimized for 438 microns and the second of 37 pixels optimized for 855 microns. Both are hexagonally close-packed, with each pixel having diffraction-limited angular resolution. Conical horns and single-moded waveguides are used to couple to the submillimeter beams, minimizing the bolometer background loading. A filter changing mechanism allows operations of the arrays at 350 and 750 microns. Single 'photometric' pixels are provided optimized for operation at 350, 600, 750, 1100, 1400 and 2000 microns. The instrument will have bolometers sensitive enough to reach the photon-noise sensitivity limit at both wavelengths, corresponding to an optical noise equivalent power (NEP) of 1.6 x 10 to the -16th WHz exp -1/2. This is achieved by cooling to 0.1 K, using a dilution refrigerator.