1 Ann Van Lysebetten CO 2 cooling experience in the LHCb Vertex Locator Vertex 2007 Lake Placid 24/09/2007

Outline Ann Van Lysebetten Vertex2007, Lake Placid  VeLo Introduction  VELO CO 2 Cooling system  Evaporator Lab performance  Cooling plant operation  Major challenges  Final Cooling plant performance  Module Thermal performance  Conclusions 2

3 VErtex LOcator Silicon sensors Vacuum vessel rf-box rectangular bellows exit window wake field suppressor kaptons Ann Van Lysebetten Vertex2007, Lake Placid

4 VELO detector half Ann Van Lysebetten Vertex2007, Lake Placid kaptons silicon sensors cooling pipes + cookies manifold Beam (7mm)

VELO cooling requirements Ann Van Lysebetten Vertex2007, Lake Placid5 Temperature silicon sensors ~-5ºC at all times  cooling temperature of -25ºC VELO Thermal Control System based on CO 2 Evaporator  Harsh non-uniform radiation environment  avoid thermal runaway in silicon  hold reverse annealing  radiation hard refrigerant  Vacuum  Direct contact between cooling and module  No connections but failsafe orbital welds  In LHCb acceptance  low mass system  No mechanical stress on the module  Cooling capacity up to 800W/half

The CO2 cooling principle No local evaporator control, evaporator is passive in detector prim. System H 2 O 10  C Sec. System (freon) Tert. System (CO2) Detector waste heat Tertiary System: two-phase accumulator controlled system 6 Ann Van Lysebetten Vertex2007, Lake Placid

7 Ann Van Lysebetten Vertex2007, Lake Placid Accumulator pressure = detector temperature Transfer tube heat exchange brings evaporator pre expansion per definition right above saturation Saturation line Capillary expansion brings evaporator blocks in saturation Detector load The CO2 cooling cycle

The implementation Vertex2007, Lake Placid Evaporator : VTCS temperature ≈ -25ºC Total Evaporator load ≈ Watt Completely passive Accessible and a friendly environment Inaccessible and a hostile environment R507a Chiller 6 2-phase Evaporator 5 4 Cooling plant: Sub cooled liquid CO 2 pumping 12.5 kg CO 2 per half CO 2 condensing to a R507a chiller CO 2 loop pressure control using a 2- phase accumulator Redundancy with spare pump and backup chiller Control of the system by Siemens PLC Ann Van Lysebetten 8

9 The cooling plant CO 2 unit freon chiller 9 Ann Van Lysebetten Vertex2007, Lake Placid 3 CO 2 pumps Accumulators Heat exchanger 2 Compressors (Air and water chiller)

10 Accumulator CO 2 pumps Compressors Ann Van Lysebetten Vertex2007, Lake Placid valves

Installation at CERN July- August 2007 CO 2 Unit Freon Unit Controls PLC Ann Van Lysebetten Vertex2007, Lake Placid11

12 23 parallel evaporator stations + Al cast cooling blocks vacuum feed through capillaries and return hose liquid inlet vapor outlet PT100 cables capillaries  inner =0.5mm The Evaporator Ann Van Lysebetten Vertex2007, Lake Placid

13 Ann Van Lysebetten Vertex2007, Lake Placid 23 parallel evaporator stations + Al cast cooling blocks vacuum feed through capillaries and return hose liquid inlet vapor outlet PT100 cables capillaries  inner =0.5mm The Evaporator

14 Mass flow Mod25 Mod16 evaporator total mass flow [g/s] temperature [ o C] annular gas+liquid flow nominal flow = 12 g/s dry out Evaporator Lab Performance Ann Van Lysebetten Vertex2007, Lake Placid heat load 1.4x nominal

From room temperature to set-point of-25 ºC Ann Van Lysebetten Start-up in ~2 hours A B C D Pump pressure (Bar) Accumulator pressure (Bar) Pumped liquid (ºC) Evaporator (ºC) Transfer return (ºC) Accu heating/cooling (W) Accu level (%) time Temp (  C), Pressure (bar), Level (%) Operation: start-up 15

Ann Van Lysebetten Major Challenges 16 Hardware concerns Pumps problems for cold start-up  sphere valve secured by a spring pump-membrane failure as result of vacuuming  pump filling now done by flushing. pump discharge burst discs replaced by spring relieves Heat exchanger from food industry (no mixing between coolants) + reinforced to withstand 200bar Safety Procedures Accu working pressure 130bar, V =14l  European directive for high pressure vessels  CE certification PLC control loops Accu control see next slides Vertex2007, Lake Placid

VTCS Accumulator Control 2PACL Start-up Heater power (%) Accu Level (%) Heater temp. (ºC) Liquid temp. (ºC) Pump inlet (ºC) Accumulator Pressure (Bar) Pump head (Bar) Decrease heater power near critical point to prevent dry- out Thermo siphon heater for pressure increase (Evaporation) Cooling spiral for pressure decrease (Condensation) Accumulator Properties: Volume 14.2 liter (Loop 9 Liter) Heater capacity 1kW Cooling capacity 1 kW Ann Van Lysebetten Vertex2007, Lake Placid17 Accumulator pressure (bar) Thermal Resistance (mK/W)

VTCS Accumulator Control Ann Van Lysebetten Vertex2007, Lake Placid18 Evaporator pressure (Bar) Condenser Inlet (ºC) Pump inlet (ºC) Evaporator liquid in (ºC) Evaporative temp. (ºC) Accu PID control loop not adequate  temperature oscillations of a few degrees Needed tuning of PID control loop to solve problem

Temperature (  C) VTCS Evaporator performance VTCS Evaporator performance Stability and response to heat-load changes Evaporator Temp (ºC) Accu Temp ≈ Set-point (ºC) Detector Power (Watt) 600 Watt Accu level (‰) Accu Cooling Power (Watt) Pumped Liquid Temp (ºC) Ann Van Lysebetten Vertex2007, Lake Placid Power (Watt) 19 Temperatures stable without pressure =-25ºC: Accumulator temp: -24.8ºC Evaporator temp(No Load): -23.4ºC Evaporator temp(600 W Load):-23.0ºC Stabilization time from 0 to 600 Watt: ca. 7min Temperature stability: <0.25ºC

20 Ann Van Lysebetten Vertex2007, Lake Placid Module Cooling Cooling system at -25 o C Module Unpowered Module Powered Total Chip Power : ~19W 2 NTCs to monitor temperature on hybrid NTC0 NTC1

21 Ann Van Lysebetten Vertex2007, Lake Placid Module Cooling & Performance Right/C halfLeft/A half  T(Setpoint – NTC1) Cooling system to silicon Measurement conditions not exactly as! final system (vacuum, not all modules cooled simultaneously, …) Small variations in power consumption, modules assembly, evaporator stations  variations in  T  T(Cool. Cookie-NTC0) Transfer cool-module  T(NTC0-NTC1) Module performance  setpoint-cool. Cookie) with setpoint of -25  C: with setpoint of -25  C: (-4.2±1.4 )  C (-5.2±1.5)  C Min  C Max  C Min  C Max  C

Conclusions Ann Van Lysebetten Vertex2007, Lake Placid22  All stringent requirements met  Setpoint temperatures go down to ~ -35  C  System proves stable operation:  without loads/with loads up to 800W  Module thermal performance + CO2 cooling at -25  C  All modules at all times below 0  C  Low mass system without mechanical stress on module  Redundancy built in  VELO CO 2 cooling system is installed and commissioned  PLC control successful  all routines implemented  1 button start/stop for main system Looking forward to enter the final commissioning phase with the VELO installed!

Back Up Slides Ann Van Lysebetten Vertex2007, Lake Placid

24 The cooling plant: CO 2 unit CO 2 -part 24 3 CO 2 pumps Ann Van Lysebetten Vertex2007, Lake Placid Accumulator Heat exchanger

25 Ann Van Lysebetten Vertex2007, Lake Placid The cooling plant: Freon unit 2 Compressors (Air and water chiller)

26 VELO detector half Ann Van Lysebetten Vertex2007, Lake Placid kaptons silicon sensors cooling pipes + cookies manifold Beam (7mm)

Main chiller performance –Dynamic range of main chiller works properly. –Full operational range (0 to 1800 Watt) possible in evaporator range (-25 º C to -30 º C) –Isolation needs improvement around injection valves –CO2 condensers/ Freon evaporator works beyond expectation (Hardly no dT between Freon and CO2 ) Back-up chiller performance –Able to maintain an un-powered CO2 evaporator at -10 º C Stand-alone test results of the VTCS cooling plant (No external evaporator, cooling over by-pass)

Transfer line Operation Transfer line Operation (Internal heat exchanger) [10] Evaporator pressure (Bar) [13] Condenser Inlet (ºC) [1] Pump inlet (ºC) Accumulator set-point [5] Evaporator liquid in (ºC) A B C B C Transfer line temperature profile A: Condenser and evaporator single phase B: Evaporator 2-phase, condenser single phase C: Both evaporator and Condenser 2- phase [14] Accumulator pressure (Bar) [10] Evaporative temp. (ºC) A Evaporator side Cooling plant side Ann Van Lysebetten Vertex2007, Lake Placid