An Instrument Proposed for Gemini
Peter J. McGregor , Peter Conroy , Gabe Bloxham , Jan van Harmelen, PASA, 16 (3), 273.
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The NIRI Legacy
NIRI Cryostat
The NIFS layout (Fig. 1) is based on the realisation that significant cost savings will arise from packaging NIFS in an identical container to that used for NIRI (Young et al. 1998). NIRI is the near-infrared imager being constructed by the University of Hawaii for Gemini North. It uses a cylindrical dewar with hexagonal cross-section mounted transverse to the optical axis. A 40 mm thick 6061-T6 aluminium optical bench is mounted inside the dewar on titanium struts. The NIRI OIWFS is mounted on one side of this optical bench, while the NIRI camera is mounted on the other side. We propose duplicating the NIRI cryostat and all NIRI components on the OIWFS side of the optical bench, except the NIRI beamsplitter wheel. The beamsplitter wheel will be replaced by a fixed mirror which directs the fixed-format science field to the camera side of the optical bench. The NIFS IFU spectrograph will replace the NIRI camera on this face (Fig. 4).
This packaging solution permits fast-tracking much of the NIFS construction, as well as providing a proven design for the OIWFS. The NIRI focal plane mask wheel will provide a convenient location at the telescope focal plane for inserting the occulting spots which may be required to probe galactic black holes on small scales. The detented Geneva drive used for the NIRI beamsplitter wheel will be adapted to the NIFS grating wheel. The NIRI science detector focusing mechanism and the NIRI structures for mounting associated control electronics will also be duplicated for NIFS. Duplicate NIRI components will be constructed in collaboration with the University of Hawaii.
NIRI Control System
The wholesale adoption of much of NIRI means that the NIRI mechanism and temperature control systems can also be duplicated to control NIFS with only relatively minor modification. NIFS will use the same Phytron cryogenic stepper motors used in NIRI and the same Hall effect sensors used to encode the NIRI mechanisms. NIFS will have fewer mechanisms in the science instrument, leading to a slight reduction in the control system complexity. The OIWFS will use a Rockwell
1024 x 1024 detector array and an SDSU-2 array controller, as does NIRI.
The main area in which the control systems for NIFS and NIRI differ is the science detector controller. NIRI uses a
1024 x 1024 SBRC ALLADIN array and the NOAO Wildfire detector controller. NIFS will use a
2048 x 2048 Rockwell HAWAII-2 array and an SDSU-2 detector controller with coadder boards. The SDSU-2 controller includes a standard VME interface to the detector Input-Output Controller (IOC).
NIRI EPICS Software
The close similarity with the NIRI control system means that the EPICS software developed for NIRI will be directly applicable to NIFS with only minimal modification. The OIWFS Component Controller (CC) and Detector Controller (DC) will be directly applicable to NIFS. The NIRI engineering software interface, Instrument Sequencer (IS), and science instrument CC will require only minor modification to remove mechanisms and rename the grating wheel components.
The major EPICS software development envisaged is in the science instrument DC which will interface to an SDSU-2 controller. EPICS code may be available for aspects of this development through the NOAO workpackage to deliver SDSU-2 controllers for optical CCDs.
Next Section: NIFS Design Concept
Title/Abstract Page: Near-Infrared Integral-Field Spectrograph (NIFS):
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