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SCUBA-2 Polarimeter

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

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SCUBA-2 Polarimeter

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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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