Category Archives: Hardware

The SAO phasing prototype visits MagAO

“Without phasing, there’s no real reason to build the GMT.”
-Andrew Szentgyorgyi

The biggest optical/infrared telescope in world will be the Giant Magellan Telescope, which will be built on a nearby mountain peak within sight of the Clay and Baade telescopes at Las Campanas.  The telescope will have 7 primary mirror segments and 7 adaptive secondary mirrors, similar to the Magellan AO system.

The 25 meter diameter Giant Magellan Telescope

The 25.5 meter diameter Giant Magellan Telescope

Photograph of the GMT site from the Magellan footpath.

Photograph of the GMT site from the Magellan footpath.

If we could build any optic we wanted for the primary of the GMT, we would probably build a monolithic 30 meter diameter (or larger) mirror made of a single piece of glass, with a thin face sheet and a honeycomb lightweight structure on back.  However, at the moment, the largest mirrors in the world are built in the Steward Observatory Mirror lab under the bleachers of the football stadium at the University of Arizona and are limited to a diameter of 8.4 meters.  Depending on who you ask, this 8.4 meter limit comes from either the distance between the columns underneath the stadium bleachers, or the size of an underpass on the highway leading from Tucson.

An 8.4 meter mirror being polished in the Steward Observatory mirror lab underneath the football stadium bleachers.  Making mirrors larger than this will require a larger football stadium.

An 8.4 meter mirror being polished in the Steward Observatory mirror lab underneath the football stadium bleachers. Making mirrors larger than this will require a larger football stadium.

Because of this limit, the GMT is designed to take 7 of the largest mirrors that can be made and combine them to form one giant 25.5 meter primary.  For this to be possible, the seven 8.4 meter segments must be “phased” to a fraction of a wavelength.  That is to say, they must be aligned to each other so that they act as if they are one large continuous mirror.

To achieve the phasing of the GMT segments using off-axis natural guide stars, SAO and our collaborators at GMTO and Flat Wavefronts have designed a sensor that creates dispersed interference fringes using subapertures spanning the 12 segment boundaries.  Phase shifts across the segment boundaries manifest themselves as tilts in the fringes.

Segment boundary subapertures for the dispersed fringe phasing sensor.

Segment boundary subapertures for the dispersed fringe phasing sensor.

Simulated fringes from one subaperture showing 0 piston phase difference (left) and 10 microns (right).

Simulated fringes from one subaperture showing 0 piston phase difference (left) and 10 microns (right).

To test this sensor technology, SAO has built a phasing prototype that simulates 6 of the GMT segment boundaries working in conjunction with the Magellan AO system.  Our three nights at the end of the MagAO run turned out to be a success.

Six sets of fringes as seen by the SAO phasing prototype working in conjunction with the MagAO system.

Six sets of fringes as seen by the SAO phasing prototype working in conjunction with the MagAO system.

The SAO phasing prototype team.  Clockwise from top left: Derek Kopon, Alan Conder, Ken McCracken, Jared Males, Laird Close, Dan Catropa, Brian McLeod, Bill Podgorski.

The SAO phasing prototype team. Clockwise from top left: Derek Kopon, Alan Conder, Ken McCracken, Jared Males, Laird Close, Dan Catropa, Brian McLeod, Bill Podgorski.

We obtained phasing data both on-axis and off-axis, with AO on and off, and at two different wavelength bands (I and J).  This data, and data that we gather during another run possibly in February, will inform the design of the GMT phasing sensor, scheduled for first light in the next decade.

Lastly, a “song of the run:”  Phazing, by Dirty South:

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Getting ready for MagAO 2014B — spare Clio solid nitrogen pump

We’ve had a few meetings lately to prepare for our upcoming 2014B run in Oct–Dec. This will be our second regular science run, and our operations are becoming more smooth and efficient, so we are going to have a more streamlined personnel plan. It will also be our longest run yet (37 nights!).

We are laying in for spares and planning improvements in our operations. One spare Phil has gotten for Clio is a spare pump for pumping on the liquid nitrogen chamber in the dewar to bring the temperature of the detector from 77 K (liquid nitrogen) down to 55 K (solid nitrogen) by lowering the pressure. This spare pump is coming to us from the LBT where it used to be a vacuum pump, and while it is no longer strong enough to deliver a true vacuum, it is strong enough to lower the pressure to solidify the nitrogen in the dewar. It is a Leybold Oerlikon EcoDry M 30 Dry Piston Vacuum Pump.

New Clio pump technical info, from Phil:

The current Clio pump is specified to reach an ultimate vacuum of 5 Torr (7 mbar). This allows the solid N2 vessel to be at 50-51 K. We typically regulate ~5 K above this or 55 K. The new EcoDry pump has an achieved lab pressure of 0.11 Torr. This will put the solid vessel at ~42 K. This suggest we could regulate as low as 47 K on the detector.

Therefore, on this next run, we will explore new setpoints and the effect on detector performance. Thanks Phil!

Here are Laird and Kim (CAAO Project Specialist) working on shipping the spare Clio pump to LCO. It weighs ~130 lbs and is 50 cm long x 30 high x 30 cm wide, and uses 120 V AC. It will be quite at home in the pump room.

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MagAO Commissioning Day 9 – Nighttime Edition: Incorporating Clio

Today was a busy day, and we began splitting MagAO’ers into day and night crew.  See Derek’s awesome post for the bulk of the day’s tasks: aligning the CRO and ASM.

The next major happening was mounting Clio to the NAS.  Even though we didn’t play the theme from Top Gun as we did it (sorry Phil!), it was an exciting moment.  This is the first time our infrared camera officially met our optical camera and our AO system!  They are together at the telescope at last!

Clio, VisAO, W-unit, Nas, ASM, Clay: So happy together!

Here’s how it happened:

Removing Clio from the support cart with the crane — under PI Phil's watchful care

Attaching Clio to the NAS ring — under Phil's watchful care

Clio at the Nas, flanked by Phil and Katie

Left: Phil and Clio instrument. Right: Clio electronics rack and Phil.

Phil, Katie, and Laird then aligned Clio’s cold pupil stops to the ASM.

Heave-ho: Shimming Clio to align the cold stops

How's it look, Phil?

LCO crew were busy as always, making everything work smoothly for the run.  Here, Mauricio brings up LN2 to fill Clio’s dewar, and Pato optimizes the PID loop that rotates the Nas while the telescope tracks and slews:

Mauricio brings up LN2 to the Nas platform to fill the Clio dewar

Pato feels for vibrations as he optimizes the PID loop tracking and slewing the Nas rotater

 

Quotes:
Alfio: “What is this mirror cover?”
Laird: “Oh you’re so cute Alfio.”

Phil:  “I don’t lean on Clio.”

Phil:  “Used to be, we only had 1 actuator.”

Povilas: “Can 14 mm be considered a shim? That’s more like a structural member.”

Simone has a key to Galileo's house.

Katie: “Hey Jared, how’s it going with the CRO?”
Jared: “I dunno. It’s all in Italian.”

Jared: “The number of Illuminati asking me questions is daunting.” (That would be Simone Esposito himself, as well as suspected members Laird, Phil, and Armando — see our paper for more info.)

 

Armandino

Jared: “I’m pretty sure I would throw myself off the catwalk if Armando thought it would help.

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