<p> HET Dome Seeing Evalution/Recommendations/Meeting Notes</p><p>Wednesday, 13 June 2001 Participants: Ed Barker , John Good, Phil Kelton, John Booth (scribe), John Vause, Tony Distasio, Jim Fowler, Mark Adams (morning), Rob Robinson (afternoon), McDonald Observatory/HET Chas Cavedoni, Gemini/UKIRT Chuck Claver, NOAO/WIYN Larry Ramsey by telecon from Penn State</p><p>(Notes from prior evening’s walkthrough on page 4)</p><p>Presentation by Barker (incompletely recorded here) Questions We Need To Answer: Is the basic recommendation of the M3 report to ventilate the ring wall and dome valid?: Size, number of openings Is Temcor concept for ventilating dome panels valid Need prototyping? What is the optimum design wind speed? Dust considerations – a problem or not? Need to upgrade dust protection for instruments, payload? Do wee need to dump heat remotely? Insulate dome? Do we have adequate flushing of the tracker area? More stuff here on this slide</p><p>30% of the time, external wind speed is less than 10 mph</p><p>Slide 7 Recommendations Cut 14 opening in the upper portion of the ring wall 10x10 ft covered by powered “garage door”, bottom opening 9 directional louver panels per opening Install up to 20 Temcor vents</p><p>Slide 8 Assumptions in M3 Report (some clearly wrong) HET: Typical operations has thermal change of 1 deg C/hr 0.4 deg C is delta T for 0.15” in seeing error budget Top 4 inches of concrete will track air temp change – NO Any steel less than ¾” thick will track air temp change - ?? Design wind speed 9 mph Heat Loads (exposed thermal masses) – not accurate (Heat load table) WIYN draws air through the telescope structure itself, exhaust to the outside, not recirculated.</p><p>Chas Cavedoni comments: Need to more accurately quantify heat loads in the building, day/night, summer/winter Want dome air recirculating with internal fans, might avoid need for Temcor solution. Insulate dome: Lowers radiant heat issue, lowers electrical costs, almost a no brainer Tracker Electrical Bay: Liquid air heat exchanger and insulate better (in process) Tracker payload: Install glycol/air heat exchanger at payload and enclose volume, already know how to do glycol here, no psychological barrier as in other facilities. Maintain concrete floor at lowest temperature expected: False spectrograph room ceiling, cooling possible, A/C unit Downdraft fans: Increase fan size for still air night, exhaust air to remote thermal extraction facility</p><p>Chuck Claver comments: Metrology: Characterize thermal environment, floor, concrete, have overlooked thermal environment inside Spherical Aberration Corrector (SAC), put at least one on eache mirror, one in front of each mirror, one mid-way between M2-M3, M4 –M5 Agrees with Cavedoni with dome ventilation, internal dome air mixing for daytime control. Nighttime control a la M3 will give consistent results. This is our one opportunity to get this done: We have momentum now. Put in Temcor vents Max out the size of the ring wall vents, go to 14’, mitigates against low wind case, 95% of nights, maybe give up on downdraft fans and use as passive vents or not since bad surface air. Worry first about large surface areas, floor Quartz halogen lamps, 8KW, leave off Relocate A/C ring tube to where lamps are now Not as thrilled about gylcol on the telescope as Cavedoni, Booth Best predictor of nighttime low is last nighttime low Install accelerometers on payload; can monitor windshake all the time (Ramsey, Booth: How to relate accel to amplitude, image quality? Would like to have high speed video to correlate, understand. But that’s just us.)</p><p>Trades between insulating structure/truss and cooling structure a la WIYN</p><p>Barker, let’s hear now from mountain staff:</p><p>John Vause: Getting “Kolpak” thermal enclosure for under the mirror array (around the Tracker Electronics Bay) Getting proposal from Trane on glycol chiller to cool this, other things in dome. 100 CFM off of the tracker, dissipating ~3KW. Chas question: Does this work? Concern that we’ve lost 2KW of the 3KW on the way out the dome. Ensuing discussion about cooling payload on place as proposed by Chas vs. the air extraction. Need to decide our path here. The critical and related issues/goals for payload heat source mitigation: 1. Mitigate seeing effects of thermal plume – current main objective 2. Minimize seeing effects at SAC 3. Minimize collection of dust on optical surfaces, instrument mechanisms. This is currently a serious problem for LRS, SAC, and the Optical Bench optics. 4. Retain (relatively easy) access to payload</p><p>Chuck’s concern about DIMM measurements: Relevant parameter to extract from DIMM measurement is r0. Use r0 to convert to what you want. Range of 0.9 0.8 0.7 can get an artificially low value for “site seeing” as r0 approaches and exceeds the separation of the DIMM apertures, which is what exactly? Paper PASP, Glindemann, Andreas, “Tip/tilt for large telescope”, maybe 1996, another paper on the CHARM tip/tilt system, good references.</p><p>Tony Distasio described the 2-5 um camera, measures temperature differentials, has local measurement capability, resolution to 0.1 deg F though this not calibrated yet, </p><p>Discussion about temperature sensing</p><p>Chas: Missing temps: Dome skin, floor skin, pier skin, internal air, top end, basement, dew point, earth, wind speed</p><p>Chuck: Time series temperature data is most critical. Camera OK for periodic monitoring and discovering leakages, singular sources like Upper Electrical Room thermal print-through to dome floor. Don’t be too distracted by intense but small hot spots vs. huge, lower delta T surfaces like the floor and pier.</p><p>Ed: What about air flow over the primary? Chuck: Suspects this is lower priority, wait and see. Dome flushing should be adequate to cool segments. Chas agrees.</p><p>Ed: Boundary condition issues</p><p>Motorized louvers vs. rollup doors. Open from the bottom vs. open from the top. 4-m uses giant insulated louvers, get uniform air height all the time, brass seals instead of rubber.</p><p>List with ranking from afternoon of 13 June, 82-inch Library</p><p>Items In Work: Kolpak (meat locker) and heat exchanger for zero thermal gradient Tracker Electronics Bay and CryoTiger under PM array Glycol chiller to service all in-dome heat exchangers Imaging Budget (who is doing?)</p><p>High Priority Items: Dome Ventilation System (DVS) – M3+++, design windspeed?, panels vs. louvers, size, number, shape Includes Ring Wall and Temcor projects Recirculating A/C: Just change Ops procedure when A/C fixed, top vents stay open Leave 8KW halogen lamps off. Disable? Just change Ops procedure Mixing fan to de-stratify dome environment, keep top end of telescope cooler Insulate Pier Quantify Heat Loads (Metrology: Campaign and analysis) Metrology: Many probes, some anemometers, archived data Insulate dome (at same time as Temcor vent installation) Tracker Payload Thermal Mitigation Includes upper half (electronics cooling) and lower half (SAC seeing control) Subset of this group should visit Kitt Peak in two weeks</p><p>Areas to Research Outside Thermal Control – “white gravel” Remote Thermal Dumping Thermal camera – use, calibrate DIMM Cal. Issues</p><p>Lower Priority Issues: Windshake characterization – accelerometers. (Trying to have this problem.) Control Dome Floor delta T Downdraft fan issues Control by surface area Insulate Structure or not Use of “fringing” to analyze tracker area seeing Air flow near PM: Wait and see DVS should solve. CCAS ventilation Upper Electronics Room thermal</p><p>HET Dome Seeing Evalution/Walk-Through</p><p>Compilation of notes and ideas from all participants evening of 11 June. See above for relative priority rankings.</p><p>Participants: Ed Barker , John Good, Phil Kelton, John Booth (scribe), consultants Chas Cavedoni, Gemini/UKIRT, Chuck Claver, NOAO/WIYN</p><p>Safety issues: Install gate on catwalk at ladder, opening toward catwalk, similar to 107-inch gates. Cage on ladder to shutter Cage on catwalk ladder, upper end</p><p>Questions: CFM coming out of the Dragon Snout?</p><p>Do: Get temperature profile in dome, air and structure, with height Temperature probes on large surface areas, like pier and floor. Get temperature profile inside the SAC, one per mirror, air in from of mirrors, two midway between mirrors. Temp coming off LRS cal system? No, fiber fed. Find out about glycol. Bad with zinc fittings, white milky substance, Chas sees these inside the pier on glycol fittings. Swimming pool of AIR inside the pier, filled with red herrings.</p><p>Possible Actions: Revisit payload cooling, bring glycol to payload, shower cap, internal circulation Kill halogen lamps, just don’t use. Big recirculating fan blowing air up to the top of the dome, mix air in the dome. Include power dissipation of motor. Either mount on catwalk or on floor. Vent placement in dome</p><p>Dome insulation Close off make up air, just do make up air. JLG, electrify Insulate/cool pier sides, top. Quantify transient heat load of all steel, and pier, heat transfer rate in low wind conditions vs. CA of vents, wind speed at vents and in the dome.</p><p>Move the fluorescent lights to make room for outside dome vents. Deal with A/C vent, Tom, “all you gotta do” is raise the plenum</p><p>Operational Strategy for downdraft fans – increase size, or just open up and don’t use, something.</p><p>Floor insulation OK? Cool the floor like at Mayall 4-m? Probably not necessary.</p><p>Down in the spectrograph room: Box in ceiling with drop ceiling, batting, and cool plenum between drop ceiling and waffle concrete ceiling. Kill heat pumping from spectrograph room.</p><p>Install some kind of dedicated temperature sensing network with some number of sensors. Engineering mode and ops mode. </p>