SOFIA Mirror Coating System Description and Components.pdf

23 October 2023

SOFIA Mirror Coating System Description and Components List

Mirror Coater Functional Description The Mirror Coater’s primary function is to aluminize the SOFIA Primary Mirror to a coating thickness of approximately 200 nm.

The Mirror Coater has a removable lid, and when removed the SOFIA Primary Mirror Assembly (PMA) is loaded, face down at mid-height in the vessel. Air evacuation for both the volumes above and below the PMA takes place, by sequentially rough pumping followed by Meissner Trap operation, followed by cryopump operation. In a typical mirror coating run, the roughing pumps are able to evacuate the chamber to a pressure of 15 mTorr within 2.5 hours. The Meissner Trap surfaces are next cooled to freeze out any present water, then the cryopumps are engaged to pump the chamber down to a pressure of less than 5 μTorr. The Mirror Coater also includes a Glow Discharge System for cleaning the surface of the mirror while at low pressure and prior to aluminization. A Filament Deposition system is then used for aluminization by melting and evaporating aluminum which is pre-loaded on an array of tungsten filaments.

1. The Mirror Coater consists of the following:

1.1. Main vacuum vessel

1.1.1. Vacuum Vessel: 13.2’ high by 13.9’ wide stainless steel cylinder with 3-leg floor mount, with approx. 28 peripheral surface vacuum seals

1.1.2. Vacuum Vessel Top Head: 2.6’ high by 13.9’ wide, with lift lugs

1.1.3. Numerous passive components internal & external to Main Vacuum

Vessel

1.1.3.1. Mirror Seals (fixed and movable)

1.1.3.2.Mirror Support Assembly (3 brackets) 1.1.3.3.Internal Platform (floor assembly) 1.1.3.4.Manway (24”) 1.1.3.5.Platform and Ladder Assemblies

1.2. Rough pumping system

1.2.1. Two-stage conventional vacuum pumps (Roots Blower, 500 m3/hr + Rotary Piston Pump, 200 m3/hr)

1.2.2. 6” rigid roughing line

1.2.3. Two 2” rigid cryopump roughing lines

1.2.4. Pump vent system

1.3. Meissner Trap system

1.3.1. Two LN2 cooled Meissner Traps (internal to Main Vacuum Vessel, 3.5 m2 each)

1.3.2. Conventional ¾” (insulated) plumbing

1.3.3. Two waste GN2 vents

1.4. Cryopump system

1.4.1. Two GHe refrigerated light molecule traps (CVI 20” each)

1.4.2. Two GHe compressors with 1” flex lines (CVI 5.5 KW each)

1.5. Glow discharge system

1.5.1. GAr supply lines

1.5.2. Glowrod Assembly (internal to Main Vacuum Vessel)

1.5.3. High Voltage DC Supply (3 KW)

1.6. Deposition system

23 October 2023

1.6.1.1. Filament Array (internal to Main Vacuum Vessel, bus bars + 63 tungsten filament mounts)

1.6.1.2. Filament Power Supply (63 KW)

1.6.1.3. Deposition thickness sensor

1.7. Vent system

1.8. Control system

1.8.1. PLC with touch screen interface

1.8.2. Vacuum gauge and thickness sensor controllers

1.8.3. Mirror temperature sensor

1.8.4. Five vacuum gauge clusters

1.8.5. Ten automated valves + eleven hand valves

1.8.6. Computer interface to PLC

1.8.7. Power cabinet, controls cabinet

1.8.8. Dozens of instrumentation cables wired around the chamber itself

1.8.9. Hundreds of signal wires between the control cabinet and the power cabinet

1.9. Power systems

1.9.1. Main electrical supply

1.9.2. Main and backup pneumatic supply

1.9.3. High voltage, low current supply for glow discharge

1.9.4. Low voltage, high current supply for deposition

1.10. Vacuum Vessel Top Head Support Frame

2. Additional GSE: These tools and equipment are used for handling the Primary

Mirror Assembly (PMA) and preparing and coating the Primary Mirror

2.1. PMA Lifting Device (PLD)

2.2. Second Load path Structure (SLS)

2.3. Coating Test Bracket (an arc-shaped structure that holds coating samples)

2.7. PM Cleaning Scaffolding

2.8 Inner and Outer Stripping Seals

2.9 PMA/MCF Interface components – Pads

2.10 Fluid Catchment hardware

2.11 Other Lab furnishings, stools, clean room vacuum cleaner, lighting