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Vertex2013

Operational aspects of the VELO cooling system of LHCb Eddy Jans ( Nikhef ) on behalf of the LHCb VELO group. Introduction Main components and operation principle of the system Issues : how to prevent and to tackle them Keep the detectors cold 24/7 Summary & outlook.

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Vertex2013

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  1. Operational aspects of the VELO cooling system of LHCb Eddy Jans (Nikhef) on behalf of the LHCb VELO group • Introduction • Main components and operation principle of the system • Issues: how to prevent and to tackle them • Keep the detectors cold 24/7 • Summary & outlook 19 September 2013 Vertex2013

  2. Introduction • VELO-module is double-sided (300 mm, oxygenated, n+-on-n) and • operatedin vacuum, • Strip closest to the beams is at 8.2 mm, • Per double-sided module: • 2x16 frontend chips that • together dissipate~20 W, • 4 NTCsgive temperature • readings • Two movable detector halves • with 21 VELO + 2 PileUp • modules each(400 W/side) NTCs 19 September 2013 Vertex2013

  3. CO2 connections module base is kept at +20 oC One detector half 0.3 mm thick RF-box Vacuum tank frontend chips cooling block Detectors are operated in a secondary vacuum  absolutely no leaks allowed. Orbital welding or vacuum brazing of the pipes. All tested at 170 bars. 19 September 2013 Vertex2013

  4. Some cooling considerations • in 1999 it was proposed to use CO2 as refrigerantfor the vertex • detector of LHCb [LHCbnote 99-046], • CO2is radiation hard, • CO2has a high latent heat • value  can usesmall • diameter capillaries  small • amount of dead material in • the acceptance, • stainless steel capillaries: • Finner=1 mm, wall thickness • 0.25 mm • system uses bi-phase CO2 via • the accumulator controlledmethod. cooling blocks 19 September 2013 Vertex2013

  5. Pressurex Enthalpy diagram of CO2 critical point At -30 oC: 300 J/g mass flow: 10 g/s per module: 0.43 g/s full evaporation130 W liquid CO2-speed: 28 cm/s all-gas speed: 240 cm/s liquid phase gas phase bi-phase area bi-phase area pressure [bar] pressure [MPa] -30 oC isothermal cooling vapourquality 0 1 enthalpy [kJ/kg] 19 September 2013 Vertex2013

  6. The accumulator controlled cooling cycle accumulator f=80 mm P7 insulation sub-cooled liquid in bi-phasereturn 5 only passive components in the radiation zone Heat out Condenser Heat out R507a chillers 6 Heat in Heat in 4 3 2 evaporator 1 55 m transfer line restriction pump vapor liquid Pressure 3 bi-phase 2 12: pump increases the pressure of the sub-cooled liquid 23: heat exchange in the transfer line brings evaporator pre-expansion per definition right above saturation point, since (E2-E3) = -(E5-E6) 34: pressure drop in restriction andexpansion in capillary brings CO2 in cooling blocks in bi-phase state, 45: isothermal cooling via evaporation 56: warming up of incoming sub-cooled liquid 61: condensation and cooling of the CO2 P7 6 1 4 5 Enthalpy 19 September 2013 Vertex2013

  7. Maincomponents of the system • evaporative CO2 cooling system • “independent” system for either side • PLC-controlled • 2.5 kW water-cooled chiller at –40oC • 1 kW air-cooled backup chiller at -25 oC • 55 m CO2 transfer lines • 10 heat exchangers • 8 actuators • 9 heaters • 31 pressure sensors • 192 temperature sensors • 350 parameters monitored in PVSS • only passive components at VELO • 2*400 W heat load of detectors • 2*12 kg CO2 • Performance @ detector • main chiller: • -28 oC operational CO2 temp. • LV on: sensors @ -7 oC • backup chiller: LV off: @ -8 oC • stability < 0.1 oC 19 September 2013 Vertex2013

  8. Design considerations and operational experience • redundancy of crucial components • insulation • clogging filters • superheated CO2 • dependence on electrical power • dependence on chilled water • safety measures to prevent overheated detectors • keeping the system 24/7 cold 19 September 2013 Vertex2013

  9. Redundancy in the design • To minimise down time the system has a few redundant crucial • components: • 3 CO2 pumps, where 2 are needed, • 2 chillers, water-cooledandan air-cooled as backup, • forcontrolscrucialtemperature and pressuresensors are two-fold • implemented, • possibility to interconnect the two sides byhand, • PLC is on a 1500 VA/1000 W UPS, • PLC, backup chiller and CO2 pumps are connected to a diesel • generator. 19 September 2013 Vertex2013

  10. Insulation Liquid pumped system  cold transfer lines  good thermal insulation required. This seems trivial, but turned out not to be so in practice. Originally CERN safety regulations forced us to use Armaflex NH. Glued surfaces started to delaminate after 2 years. Renewed insulation of the transfer lines and most of the cooling plant during Winter shutdown ‘10-’11. Now foamglass covered by an Aluminium protection shieldand Armaflex AF, respectively. 19 September 2013 Vertex2013

  11. Filters Throughout the system eleven15 mm filters are installed. (5 (CO2-plant), 2(@VELO), 2(manifold), 1(main chiller), 1(backup chiller)). In one detector half we have experienced a few timesclogging filters. Replacement procedure is tricky and risk of additional dirt in the system due to difficult accessible filter houses. pressure [bar] 17 16 piece of Armaflex thermal insulation once completely blocked arestriction valve 15 2 months 19 September 2013 Vertex2013

  12. Post mortem analysis of the filters 75 mm Energy Dispersive Spectrometer analysis of an orange particle found inside the filter Scanning Electron Microscope image Many >15 µm orange objects have been observed inside the filter. They mainly contain Feand O. Before, particles containing Clhad been observed. Possibly due to connections soldered with flux for a testbeamexperiment  risk in terms of corrosion. Work extremely clean from construction to installation. 19 September 2013 Vertex2013

  13. Superheated CO2afterstartup Afterstartup we occasionallyobservein a varyingnumber (a fewall) of coolingblocks the phenomenonof superheated CO2. Issue: cooling performance is very bad becauseliquidcoolinghas much lesscooling power thanevaporativecooling. 19 September 2013 Vertex2013

  14. Superheated CO2afterwarmupandcooldown Tsilicon [oC] LV off -14 cooldown warmup of the cooling plant -22 DT=3 oC -30 time 30 minutes 19 September 2013 Vertex2013

  15. Superheated CO2afterwarmupandcooldown LV off Tsilicon [oC] Pressure  -14 Enthalpy  start adding heat vapor liquid -22 3 bi-phase 2 DT=3 oC 6 1 4 5 -30 time • Remedy: add heat by means of a dedicatedheater to bringthe • incoming CO2in the liquid+gas state. 30 minutes 19 September 2013 Vertex2013

  16. Some more superheatedCO2 Not all coolingblocksbehave the same way: - not all show superheating - whenadding heat theydon’t start boiling at the same moment silicon temperatures of 4 modules DT4 oC start adding heat 19 September 2013 Vertex2013

  17. Power cuts sensor temperature PLC and backup chillerareconnected to the power of a diesel generatorof LHCb and the PLC also to itsown UPS (1500 VA/1000 W) When the power gets cut the switch-over frommaintobackup chiller is handledautomatically by the PLC. Afterswitching back to the main chiller the system is stableafter ~20 minutes. Afterswitching on the LV the sensorsare at theiroperational temperaturesafter10 minutes.  half anhourrecovery time. -10 -20 10 minutes -30 LV on 19 September 2013 Vertex2013

  18. Failure of chilled water supply Chilled water supply, that cools the main chiller,sometimes gets interrupted. If so, the PLC switches on the air-cooled backup chiller. However, this causes the LV to be switched off also. 19 September 2013 Vertex2013

  19. Safety Operation in vacuum requires immediate reacting safety systems. Three levels. 2. SW-based:warning and interlock system 1. HW-based: interlock system Actions Conditions Vacuum-PLC LV Off Cooling-PLC HV Off Module temperatures Cooling Off Temp-boards Retract VELO Beam Conditions Monitor Emergency button 132 cooling parameters monitored Combined information of 4 NTCs per module are input to the FPGA, whichcan interlock the LV. 3 levels each: warning, error and fatal 19 September 2013 Vertex2013

  20. 3. Human-based Emergency button in the LHCb control room to power off the VELO. 19 September 2013 Vertex2013

  21. Keep the detectors cold 24/7 Vdepl NC + DNeff(=effective space charge density) • Short term: “Beneficial annealing (NA)”• Long term: “Reverse annealing (NY)” - time constant depends on temperature:~ 500 years (-10°C)~ 500 days ( 20°C)~ 21 hours ( 60°C) At the tip the received fluence is 2x1014neq/cm2 and type inversion has taken place, so the sensors should always be kept cold, (below -8 oC), in order to prevent the Vdepletion to increase due to reverse annealing. The beneficial annealing budget amounts to a handful of weeks at room temperature. We try to save it till we really need it. But the conditions of the LongShutdown1 period at LHCb make it hard to do so. 19 September 2013 Vertex2013

  22. The challenge is to keep the system operational 24/7. • Under normalconditionsthe PLC deals withcommon problems. • Goal: minimize the warm time due to • scheduled maintenance of crucial components, • repair of malfunctioningcomponents, • unexpectedproblemsduring LS1 andshutdown periods. 19 September 2013 Vertex2013

  23. Regular maintenance Yearly maintenance of the R507a chillers is performedby a specializedexternal company. Downtime~0.5 day / chiller. Yearly maintenance of the 3 CO2 pumps is donebyNikhef-technicians. Pump is unavailable for >24 hours. Effective downtime of the system: 2 hours / pump. Repair of failingcomponents So far no component had to be replaced, although a (redundant) pressuregauge stopped working in 2012, butmiraculouslyreincarnated after 6 months. 19 September 2013 Vertex2013

  24. Unexpectedproblems How do youknow a seriousproblemoccured, causing the cooling to go off and the detector to warm up ? Especiallyduring LS1. Can’t rely on a PVSS-script sending a mail or sms. Amodem and sms-routine have been installed in the PLC. antenna When a problem occurs every half hour a text message is sent to a list of phones numbers, until the cooling system is again in a proper state. Acted 6times since Feb. ‘13 due to failing services. modemwith Sunrise sim card, soworks underground. 19 September 2013 Vertex2013

  25. Integrated warm time in 2012: ~1 day 18 = 8 hours 0 -10 0 year 2012 -30 19 September 2013 Vertex2013

  26. Summary • cooling system is continuously operational since >4 years, • performance is stable and according to specs, • redundancy of crucial components has shown to pay off, • clogging filters are annoying, • good thermal insulation is less simple than it seems, • superheated CO2can be dealt with, • the warning system that sends sms-esis a great tool, • thus far the integrated warm time has been ~1 day/year, so ………. 19 September 2013 Vertex2013

  27. Outlook lets keep it cool till LS2, when the new VELO pixel detector goes in. 19 September 2013 Eddy Jans 26 Vertex2013

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