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SCUBA-2 Polarimeter Mechanical Design and Optical Discussion Meeting Agenda

Review of Mechanical and Optical Designs for SCUBA-2 Polarimeter at CDR Meeting, including FEA analysis and discussions on mirror samples, ghosting, paper publication, and project planning.

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SCUBA-2 Polarimeter Mechanical Design and Optical Discussion Meeting Agenda

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  1. SCUBA-2 Polarimeter Internal CDR meeting December 20th, 2005

  2. Meeting Agenda • Beginning of the meeting at 10h30 am • Mechanical Design Overview • FEA • Discussion • Lunch at 12h00 am • Optical design • Model • Ghosting • Mirror Sample • Paper Publication • Planning • End of meeting at 3h00 pm

  3. Mechanical Design • Mechanical Design Overview • Space envelope • Translation module • Rotation module • FEA • Discussion

  4. Space envelope • New ICD • Connector positions

  5. Translation Modules • Miniature linear guide from THK • Cage ball • Lead screw with anti-backlash nut • Miniature Maxon servo motor, gearbox and encoder • 15 seconds to go from store to operating position • Service life 1000 to 3000 hrs • Limit switch • Home and end position • Selection of limit switch to be confirm with electronic

  6. Rotation Module • Timing belt (8.5:1 ratio) • 5 mm pitch GT belt • Neoprene, fiberglass reinforced • Belt Useful life approx. 3000 hrs • Custom made timing pulley PD 324.6 mm • Efficiency 95% • Thin section bearing • Angular contact preloaded bearing pair • Solid lubricant • Friction torque max: 1 Nm at 20C, 1.6 Nm at –15C 2RPM • Lead time 16-18 weeks

  7. Rotation Module • Maxon flat motor 90Watt • Biggest motor that could fit in the allowed space • Continuous operation: 2000 rpm, 557mNm • At 20C with SF = 2.2, Speed max : 5 hz • At -15C with SF = 1.5, Speed max : 5 hz • Service life 10 000 hrs • Renishaw angle encoder • CA 280 mm

  8. Rotation Module • Cable management • Cable tack has been pre-selected • Will hold encoder and motor cable • Size of motor cable needs to be confirm • Size of track : 9.9mm x 20 mm • Bend radius 37 mm

  9. FEA • Dynamics • Modal analysis • First mode 52 hz > 12 hz • Statics in three orientation • Deformation of entire polorimeter • Deformation max 35 um • Deformation and constraint of sapphir plate • Tilt max in operation : 0.003 deg

  10. Discussion

  11. Optical design of the SCUBA-2 polarimeter CDR meeting December 20th, 2005

  12. Optical Design • Model • Image quality: remains the same with adjustment on M2 (p. 2) • Footprint & Vignetting: • for the 277 mm diameter half wave plate: no impact on the beam (p. 14) • For the 200 mm diameter sapphire half wave plate: affects the sensitivity but no vignetting (p. 15-21) • Calibration source: covers the whole beam footprint (p. 23)

  13. Optical Design • Mirror Sample needed or theoretical data sufficient? (p. 37) • Instrumental polarization: • Impact of the telescope and camera mirror surfaces (p. 39) • Impact of the polarizers (isolation) (p. 40-43 ) • Camera window and filters: unknown (p. 40-43) • Derivation of a Mueller matrix and a Jones matrix representing the sapphire half wave plate (p. 44-54)

  14. Optical Design • Instrumental polarization simulated in Zemax • Telescope + Camera : • polarization of an unpolarized beam = 0.769% (p. 57) • Ellipticity (added phase) = 0.22° (p. 57) • Telescope + Camera + Polarimeter: • polarization of an unpolarized beam = 99.80% (p. 61) • Ellipticity (added phase) = 0.32° (p. 61)

  15. Optical Design • Ghosting: • Most important ghost: retro-reflection between analyzer polarizer and half wave plate. Spot size = 127 mm dia. at detector plane (p. 70-72) • Uncertainty on the phase of the retro-reflected beam • The beam retro-reflected from the half wave plate has a phase that varies with the wavelength (p. 66, 73-74) • There seems to be no big problem in the operation mode (p. 75-82). Ghosts in the calibration mode are more important (p. 83-88). The simulation results probably represents the worst case scenario.

  16. Optical Design • Paper publication • Waveplate simulation results / experimental results • Whole instrument simulation • Publication date: • After characterization of sapphire waveplate? • After commitionning?

  17. Planning • Optical elements delivery schedule • Mechanical parts delivery • The temporary gear needs to be replaced by the final one. Need 1 week at INO to perform the replacement. • Final mechanism delivery: confirm the date of September 2006 • Waveplate test setup: • INO to provide mechanical interface data for gear holder but not gear holder itself

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