NEWFIRM Instrument
The NEWFIRM instrument includes the Dewar, guider, various electronics boxes, cryogenic gas system, and truss. Refer to the figures below to locate the various pieces. The cutaway illustration shows interior components.
The Dewar contains the cryogenic optics (7 lenses and a fold mirror), two filter wheels with a total of 14 filter spaces plus an open space in each wheel, and the detector mosaic of four 2K x 2K InSb arrays. These are incorporated into a unified Optical Support Structure (OSS). The warm collimator field lens also serves as the Dewar entrance window. Operating temperatures are 65 K for the OSS and 30 K for the arrays.
Bolted to the top of the Dewar, just above the field lens/entrance window, is the Environmental Cover Assembly. This has a warm shutter to protect the window against dirt and hazards when not in use. A system of vents allows for a continuous flow of dry N2 gas across the window to prevent fogging.
The yellow girth ring, part of the Dewar vacuum assembly, supports the load of the OSS and couples the Dewar to the external truss.
The yellow truss couples the Dewar to the telescope, and carries the guider electronics, other electronic boxes, and part of the cryogenic gas system. It is both robust and precise, carefully tuned in its deflection properties so that the warm external guider tracks the deflection of the OSS inside the Dewar.
The hardware for the dedicated guider is attached to the truss above the Environmental Cover Assembly. A plate holds two guide cameras, each mounted on a stackup of high precision X-Y-Z stages. These can access regions of the telescope focal plane adjacent to the science field on its north and south sides. These assemblies are enclosed for dust, heat, and scattered light control. Control electronics for the guiders are in a series of black boxes bolted around the upper part of the truss.
The space between the mirror cell and the Environmental Cover Assembly is enclosed by a square black baffle box for scattered light control. Dry N2 gas is also injected into this area to prevent fogging of the entrance window.
The Monsoon array controller Digital Head Electronics (DHE) box is mounted o the Dewar to the right of the Cass cage door. It provides power, control, and readout of the arrays. A top-opening panel on the box gives access to reset buttons that are used for error recovery procedure. The DHE power supplies are attached to the truss above the electronics box.
The Instrument Controller is mounted on the Dewar on the side opposite of the DHE boxes. Access is via the Cass cage walkway. The Instrument Controller provides cryogenic temperature monitoring and control, and operates the filter wheels and the Environmental Control warm shutter.
The helium gas cryogenic system has multiple components. Three cold heads are mounted on the Dewar. A black triangular plate attached to the truss holds the helium gas manifold, gas heater, gas filter, and differential pressure sensor (a safety device). These are interconnected by high pressure gas lines. Also mounted on this plate is a flowmeter for the dry N2 gas flowing to the Environmental Cover Assembly and the guider baffle box. A second flowmeter is mounted at the entry point of this gas to the Cass cage, on a panel mounted in the cage.
Updated on August 28, 2023, 3:24 pm