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OrganizationThe SCUBA-2 project is a collaboration of several observatories or laboratories. The project is lead by the UK Astronomy Technology Centre (ATC) with the partners NIST (detector arrays and readout), University of Edinburgh (Silicon micro machining), University of Wales at Cardiff (Focal Plane Unit), Raytheon (bump bonding) and JAC (infra structure). In addition a Canadian partners funded through a grant from the Canada Fund for Innovation is responsible for the warm electronics and the data reduction software. The Canadian consortium also contributes a FTS and Polarimeter module for SCUBA-2. However, these modules are managed outside the SCUBA-2 project. The ATC SCUBA-2 webpage can be found here. DesignThe heart of SCUBA2 is the Transition Edge Sensor (TES) arrays developed by NIST. SCUBA2 will have four 32x40 detector arrays at each of 850 and 450 micron, in total 10240 detectors. In order to decrease the number of wires from the cold focal plan unit the readout is time multiplexed using SQUID devices. The arrays are used bare i.e. without any fieled of view defining horns. This necessitates a very careful optical design to control stray light but makes it possible to space the detectors closer. The 850 micron array detectors will be spaced at the telescope resolution limit of Fl/2. Due to size limitations the 450-micron array detectors will be spaced with Fl, thus the same field of view with the same number of detectors. The TES detectors are kept at the transition edge between they super conducting and normal state by the radiation loading and a voltage bias. An increase in the incoming radiation will increase the device resistance reducing the bias heating. This very strong positive feedback will keep the device at a basically constant working point while the bias current is proportional to the incoming radiation. The SQUID readout is linearized by biasing the SQUID so it operates very close to a |
