SLAC Collaboration Meeting Image Quality Workshop: State of the Blanco Tim Abbott (owing much to Roberto Tighe) CTIO 2 Dec 2009 Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec

Improving image quality at Blanco We are making a concerted effort to improve the image quality delivered by the Blanco telescope. Historically, focus has been on thermal & environmental improvements. A few years ago we discovered unpredictable movements of the primary mirror on the cell, with large hysteresis sufficient to significantly affect the image quality through coma. Caused by broken radial supports, produced as a result of design flaws and poor maintenance. Our goal is now to reduce these movements to those caused by flexure alone, which makes them predictable and removable with DECam’s hexapod. Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec

Radial support refurbishment Successful shutdown April/May –All 24 H-bars replaced, all 96 bearings replaced, everything realigned –Radial “soft points” used for balance, then backed off. Now 8 months with no breaks (one scare: switch problem )

Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec Things get better - M1 displacement wrt M1 Cell Blanco M1 displacement w/r to cell (broken:15) 2007 (broken:15,21) 2008 (broken:15,21,14) N (mm) E (mm) Before shutdown (Oct2005-April2009) With New Radial Supports after shutdown, data: June 2009 Results: The M1 walk wrt cell is within a circle of maximum radius ~100um centered in the center of the mirror cell to within ~50um. (Traces include moving to NW station and to extreme positions for Tel. balancing)

5 Primary Mirror / Cell Position Data:“Jumps” Initial Position June5th (-30um) First Jump after going to Passive Mode June7th Third Jump after going to Passive Mode July 1st Second Jump June24th New Telemetry Started June 18th Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec 2009 Now realized to be a long standing phenomenon, the “jumps” are associated with active optics runaway. They have been diagnosed and partially resolved. A solution is under study as part of the TCS upgrade project.

6 (E-W)/2 Mitutoyo Data v/s Telescope RA Data filtered to be +/-5deg from DEC=-30deg Before Second Jump (June18-24 th ) After Second Jump (June24th-July3rd) Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec 2009

7 The Blanco Main mirror Cell Axial Hard Points Load Cells: y: NW z: S |: NE (note: we have a discrepancy in the naming, to be checked !!) Linear Gauges (blue arrows; and from here on called Mitutoyos), measure the E-W and the N-S displacement of the mirror w/r to the Cell. (In green: radial defining points + load cells) y z | 37.5°

N Average all 88.1% 3.8 Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec Coating Chamber Testing The low reflectance must be due to contamination because the ND, the Coating Thickness Monitor and the Film Thickness Interferogram measurements say the layer thickness is OK. Decided not to re- coat the Blanco main mirror and wash it instead given that the coating is in good condition: Av.R=88.3%,TIS=0.8 5% (new Aluminium coating: R= 89.6%,TIS=0.35%).-

Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec D80 = 0.25Arcsec = 13.86um at the prime focus The Blanco primary mirror, Original Manufacturer’s Data

Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec Zemax Model of Blanco+PFCorrector Expected d80 = ~ (Arcsec) W 1.0Arcsec 55um =+/-0.15” FieldMosaicCoor. d80 Pos.x (mm)y (mm) (Arcsec) (MOSAIC Display SKY Orientation: North- right, East-up)

Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec Measured IQ at PF ( ; red: May 2009 before correction) Z Az + 15º 30º 45º 60º 82º Aberration Term Conversion factor (Arcsec/umWF) Defocus 0.84 Spherical 0.11 Coma 0.14 Astigmatism 0.33 Trefoil 0.39 Quadratic 0.42 Measurement Tools: Hartmann Test at PF Shack-Hartmann at F/8 Where all-sky means over the Telescope Pointing Position Sky-Map shown here:

Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec Post Shutdown To Do List Status: M1 displacement w/r to cell is ~ 1/4 the max. tolerance for coma (~500um). To Do short term: Re-measure the aberration skymaps at PF and F/8 –Done, data to be reduced & analyzed Re-adjust Baseline corrections and LUTs for PF and F/8. –Pending results of observations To Do long term: Re-measure the PFC unit w/r to M1 using the laser projector and Mitutoyos. –Done, see following slides. Some analysis pending. Finish upgrading the Coating chamber and produce a reliable Al coating recipe before next shutdown. –Shutdown scheduled for ~August Coating chamber components on order. Review of procedures pending.

Laser displacement measurements With: –A laser mounted rigidly to the primary mirror in the central obstruction (centering not important). –A camera mounted on the cover of the prime focus corrector Move the telescope around on the sky and follow the spot. This measures the possible displacement of the camera with respect to the primary mirror which will contribute to reduced image quality through coma. 13 Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec 2009

Around the horizon, From North, moving West, in 30° steps 14 Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec 2009

Around the horizon, From North, moving West, in 30° steps 15 Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec 2009

Point telescope at south pole. Rotate around pole: 6 hrs east, back to meridian, 6 hrs west, back to meridian 1 hr steps. (2009 data is not corrected for mirror/cell translations.) N (mm) 16 Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec 2009

With azimuths of 30° and 120°: Move Z,NE,Z,SW,Z andZ,SW,Z,NE,Z In steps of 15° in ZD 17 Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec 2009 Note: 2009 data is not corrected for mirror/cell translations.

East/West North/South Z,W,Z,E,Z Z,N,Z,S,Z In steps of 15° in ZD 18 Tim Abbott, SLAC Collaboration Meeting, IQ workshop, 2 Dec 2009 Note: 2009 data is not corrected for mirror/cell translations.

19 Blanco Environmental Control Modify/Rebuild the primary mirror plenum. Remove mirror washing seal. –Planned for August 2010 shutdown Revise oil cooling system –Some work already under way Improved display interface for the ECS, associate with TCS, weather, rationalize –The weather part is under way Increase the capacity and modernize the glycol cooling hardware –Underway, stimulus funding Replace inoperative temperature probes, upgrade control PC, port software –Some of the repairs are under way Review protocols, motivate staff, monitor performance, tune system. It’s expected we will start using the mirror chiller/sucker, the helicopter fan, etc. Put Mag Chloride dust suppressant on the GONG/Lowell road in OCTOBER each year. Buy particle sensor. Longer term: –Consider opening up more vent area –Mount extractor fan internally near the roof, exhaust to the outside