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Functional Design of a Coating System for the Telescope Mirrors, A Recognition to Telescope of Iranian National Observatory

Mahdizadeh, Sajjad | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48324 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Moshfegh, Alireza; Khosroshahi, Habib
  7. Abstract:
  8. Functional design of coating system for the primary mirror of the Iranian National Observatory (INO) is done. This telescope has a 3.4 m primary mirror in diameter, made of Zerodur from Schott. Although similar coating systems are in use since years ago, this is the first attempt to design a system for such a large surface case in Iran. Systematic approach led us first to clarify and identifying the design requirements. Lower limit of 80% for reflectance on all wavelength range from 325-1000 nm, thickness of 100 nm with un-uniformity of 5 nm, adhesion enough to pass the selotape test and surface roughness of less than 8 nm. Study of the available methods for coating and selection of the best one has been done in the 2nd step, where we decided to use an evaporation coating system. Design strategies are picked up in the 3rd step, which are "design for safety" and "design for reliability" and are the framework of the design procedure. Coating system has been broken to six subsystem including "chamber", "vacuum", "deposition", "glow discharge", "control" and "power supply", during 4th step of this work. Functional design of the system is finally done; we have clarified duties of each subsystem, identified different parts in order to accomplish the duties, and assigned main characteristics to each subsystem as following. A cylindrical chamber of the height 3.5 m and diameter 3.8 m is our favorable chamber which moves up and down with jacks and presses the door from the bottom, which is moveable on a rail. Ultimate vacuum pressure of 10-7 mbar will be reached from two diffusion pumps at total speed of 50000 L/s, backed by a roots pump which itself is backed by a dry mechanical pump. Deposition will be done using 100 filaments of tungsten; all installed on a ring at height of 2 m from the substrate, and warming with a total power of 60 kW and evaporating of 40 g of pure Aluminum to be deposited. Glow discharge of the power of 3 kW with Argon and Oxygen ions is decided to clean the chamber just prior to the coating. A Computer equipped with a programmable logical controller (PLC) is the heart of the control unit, and transformers will be in use to supply the filament ring and glow discharge unit. The plant is capable to recoat the mirror in maximum of 2 days
  9. Keywords:
  10. Aluminum Coating ; Coating System ; Functional Design ; Iranian National Observatory ; Vacuum Chamber ; Evaporative Deposition

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