IMACS Detector System Overview

IMACS is the principal multi-object spectrograph and imager for the 6.5m Magellan I telescope.  It features an 8K×8K detector system, which is mounted in a cryogenic vacuum vessel with a combination of features that includes closed-cycle coolers, a piezo-driven flexure compensation stage, flexure control detectors, array focus control, and a composite thermal isolation truss.  The 8K×8K detector array is a key subsystem of the IMACS instrument and is crucial to the performance of the entire instrument.  These pages describe the detectors, the design of the array, and the features of the dewar. Description of the IMACS detector system The IMACS detector system consists of eight 2048 × 4096 × 15 um pixel devices.  The eight CCDs are mounted as a 2×4 array on a single base plate, housed in a vacuum vessel, and cooled to cryogenic temperatures.  The CCD mosaic is flanked on two sides by 2680 × 512  pixel  wing CCDs which may be used as image motion sensors in a future, closed-loop control system for flexure.  The IMACS detectors are operated by a custom-designed set of ccd controller electronics (see BASE). Physically, the BASE system for IMACS consists of an electronics box [4.75" × 8.25" × 10"] housing one DSP board, four dual-channel clock driver boards, four dual-channel signal processing boards, a power conversion board, and a back-plane board. In addition, there are four dual-pre-amp boards inside the dewar.  The wing chips are controlled by a separate dual-channel set of BASE electronics. Description of the IMACS dewar There are several components to the dewar assembly. The first is the vacuum vessel, which includes the dewar body, dewar mounting plate with window, side covers with pre-amp printed circuit boards, and the back plate. The second is the CCD detector array assembly, which includes the mosaic mounting plate, the thermal isolation truss, the XY flexure compensation stage, and the titanium focus flexure.  Finally, there are the bolt-on mechanisms, including the vacuum gauge, vacuum valve, cryo-coolers, and stepper motor assembly. See B. Bigelow et al, "Design of the IMACS 8K x 8K Dewar and Detector System,"  SPIE 4841 Astronomical Telescopes and Instrumentation, Kona (2002).