The NIRI Legacy

NIRI Cryostat

The NIFS layout is based on the realisation that significant cost savings will arise from packaging NIFS in an identical container to that used for NIRI. 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. The NIRI cryostat and all NIRI components on the OIWFS side of the optical bench, except the NIRI beamsplitter wheel, will be duplicated for NIFS. The beamsplitter wheel will be replaced by a fixed pick-off mirror which directs the fixed-format science field to the science instrument side of the optical bench. The NIFS integral-field spectrograph will replace the NIRI camera on this face.

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 disks. The detented Geneva drive used for the NIRI beamsplitter wheel will be adapted to the NIFS grating wheel. The NIRI integration frame for mounting associated control electronics will also be duplicated for NIFS.

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 × 1024 detector and an SDSU-2 detector 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 × 1024 SBRC ALLADIN array and the NOAO Wildfire detector controller. NIFS will use a 2048 × 2048 Rockwell HAWAII-2 array and an SDSU-2 detector controller. The SDSU-2 controller includes a standard VME interface to the Gemini detector Input-Output Controller (IOC).

NIRI EPICS Software

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.

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