Refrigeration System Status and Plans Tom Peterson, for the LSST refrigeration team

Joint Telescope Meeting - 6-8 March 2017 Outline Latest thermal requirements (Martin Nordby's analysis summary) Latest test results for the system in B750 at SLAC Some conclusions and concerns based on test results Latest refrigeration system scope plans Current layout Remaining concerns, things to be tested, near term work Top-level schedule (a few major milestones) Discussion topics Joint Telescope Meeting - 6-8 March 2017

Camera Thermal Budget and Heat Flow Document LCA-10156-A 28-Feb-17 Authors: Martin Nordby, John Hodgson, J Langton, Pat Hascall

Temperature requirements Cf: LCA-51-C, Cryostat Specification Consistent with that specification, we are targeting temperatures to be within the following ranges: -120 C to -130 C for the cryo plate, -30 C to - 40 C for the cold plate Long term running since December has been very successful Following slides summarize some results Joint Telescope Meeting - 6-8 March 2017

Extended Subscale Run Dec. 8 –> Present (200ft Lines) D Setpoint Total Load Capacity = Process Load + Parasitic Load (~17W) Small Refrigerant Leaks Detected Process Load (W)) D Setpoint Leaks Fixed Refrigerant top off Vacuum Pump Trip Vacuum Pump Fixed Process Load (Nominal) Requirement At -1250C Note: process load Qnom = 60 W Process load Qmax = 76 W Total capacity meets requirement of 93 W But little margin relative to maximum required Feedback Setpoints (-1250C, -1280C,-130 0C Process Load Power W (No Parasitic) Cryoplate Temperature 0C Evaporator set point temperatures: -125 C, -128 C, -130 C Cryoplate Temperature 0C

Extended Subscale Run Dec. 8 –> Present (200ft Lines) Compressor Power Max Allowed Sustained Compressor Power Max Allowed Sustained Discharge Pressure Compressor Power (W) or Discharge Pressure (PSI) Discharge Pressure Suction Pressure(Psi) Suction Pressure Joint Telescope Meeting - 6-8 March 2017

Cold system tests Heat and temperature requirements Essentially 300 W to 550 W per circuit Temperature -40 to -30 C Problem: a system sized for 550 W will have a frosty cold return line at 300 W unless a valve or supplemental heat source are used A solution tested successfully is a thermostatically controlled expansion valve, replacing the fixed size capillary tube expansion

Thermostatic Expansion Valve: Maintain relative constant superheat at the bulb by adjusting the valve opening

Test Results with Danfoss TUA Joint Telescope Meeting - 6-8 March 2017

Extended Run (24 hrs) Ambient Temperature Compressor Power (VxA) Return Line Temperature Power (W) Temperature (oC) Load Power Evaporator Temperature

Additional work due to running experience Many problems resolved Much better understanding: avoiding contamination, avoiding plugging, oil management Treat like a vacuum system – clean, purge, evacuate prior to filling The use of flexible polyamide hose has been very successful in reducing the liquid refrigerant volume and controlling oil transport (compared to flexible metal hose we were using) in the full 200ft system, once we understood how to clean and condition it. Successful long-term running at required capacity Some questions remain (following slides) Joint Telescope Meeting - 6-8 March 2017

Joint Telescope Meeting - 6-8 March 2017 Remaining tests – 1 Test compressor with large motor (R404A) in B750 with subscale cryogenic system Verify that with our mixed refrigerant and pressures, the power is acceptably within the manufacturer’s recommendation Lower evaporator temperature test This test verifies that we meet the requirement for the minimum survival temperature (or load power). We have done this test successfully with small evaporators but should repeat with subscale evaporator and full length transfer lines. Water chiller setpoint testing This test verifies that the refrigeration system will operate within specifications, with chilled water/glycol in the temp. range supplied by the observatory (LSE-64) Joint Telescope Meeting - 6-8 March 2017

Joint Telescope Meeting - 6-8 March 2017 Remaining tests – 2 Warm up and restart - repeatability test This test establishes the correct procedure for restarting the subscale system with long line geometry after its is warmed up and already charged (eg: how long to wait until refrigerant equilibriates). Need to establish procedure that yields repeatable performance. TMA Geometry test - oil return to compressor Risk List: CRYO-024. The TMA geometry has changed and we now have to address the elevation and rotation only. This test would simulate some of the drapes and verifies that the oil return to the compressor in the new geometry will be sufficient to avoid damage to the compressors or plugging of the evaporator . Testing of cold system expansion valves Risk List: Cryo-034. With the current requirements on capacity, without the expansion valves and with off-shelf heat exchanger, tests show very cold return line temperature at low heat loads. Tests already show the expansion valves work well to match capacity to load. We would like to select the vendor and the packaging, and have some extended running. Joint Telescope Meeting - 6-8 March 2017

Compromises regarding remaining work Descope 3rd refrigeration system - two systems instead of three (I&T system to become the summit maintenance system) Reduce testing De-scope cryogenic system heat exchanger testing Outsource heat exchanger fabrication Make minimal changes to the cold system Joint Telescope Meeting - 6-8 March 2017

Some schedule milestones with finish dates I&T Refrigerator System Final Design Review, summer 2017 (exact date TBD) Cryostat Refrigeration System Ready for Integration – 10-Nov-17 Cryostat Chamber & I&T Refrig. System Ready for Integration – 08-Mar-18 Cryostat Early Hardware & Software Ready for Summit – 6-May-19 Joint Telescope Meeting - 6-8 March 2017

Design integration issues, discussion Compressor cabinets (design and interface presentation for discussion) Layout and arrangement of cabinets Routing and arrangement of piping near and into the cabinets Discussion of utility interface Installation sequences Line lengths and layout on the telescope Variations, lengths. Length tolerance 5% for supply lines (liquid/vapor) for single system. 10% maximal difference between systems. Feedback on exact TMA/Camera refrigerant plumbing interface Joint Telescope Meeting - 6-8 March 2017

More discussion topics Discussion of thermal requirements that affect Dome seeing Pipe skin temperatures (temperature presentation for discussion) Return line temperature, issues with cold lines, condensation, frosting We need a definitive statement about line insulation (where we have it and what it is) Supply line temperatures set by aftercooler temperature (14 C) and may differ from ambient T by a lot. Difference of return lines from ambient in low humidity controlled area. (How is that kept dry? Dew point there should be < -10 C below ambient). Temperatures quickly approach ambient. Compressor cabinet skin temperature. Current plan is to cool the cabinet using via air circulation through an off-the-shelf exchanger with coolant (like an automobile radiator). Pressure standards, verification, procurement per standards (Note: Specifications in documents LSE-051 and LSE-069) Update from Shawn about TMA vendor status/questions Joint Telescope Meeting - 6-8 March 2017

Camera Integration in IR2 Joint Telescope Meeting - 6-8 March 2017

New Location of Compressors on the TMA Camera M1 Mirror Compressor Cabinets Joint Telescope Meeting - 6-8 March 2017

New Refrigeration Line Layout Joint Telescope Meeting - 6-8 March 2017

Original Refrigeration Line Layout Joint Telescope Meeting - 6-8 March 2017

Joint Telescope Meeting - 6-8 March 2017 Acknowlegements Slides and information were provided by: Gordon Bowden Alice Callen Diane Hascall Pat Hascall Martin Nordby Yongqiang Qiu Rafe Schindler Joint Telescope Meeting - 6-8 March 2017