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The SCUBA-2 project |
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Organization
The 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.
Design
The 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 their 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
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