1. CO 2 CO2 COOLING FOR THE LHCB-VELO EXPERIMENT AT CERN Bart Verlaat
GL-2008
8th IIF/IIR Gustav Lorentzen Conference on Natural Working Fluids
CO2 COOLING FOR THE LHCB-VELO EXPERIMENT AT CERN
CDP 16 - T3-08
Bart Verlaat
National Institute for Subatomic Physics (NIKHEF)
Amsterdam, The Netherlands CO 2
Copenhagen, 9 September 2008

2. Table of Contents
Introduction to Particle Physics research, NIKHEF and CERN.
Introduction to the LHCb and the VELO detector.
Explanation of the VELO Thermal Control System (VTCS).
Commisioning results of the VTCS.
Conclusions and outlook.

3. The Large Hadron Collider related experiments at CERN in Geneva
Introduction to Nikhef National Institute for Subatomic Physics Amsterdam, the Netherlands
The Large Hadron Collider related experiments at CERN in Geneva
27 km
Ca. 100m
Nikhef participates in particle physics experiments world-wide:
Particle accelerator experiments
Astro-particle physics experiments
LHC
Starts tomorrow!
(Details at the end)
Goals of the particle physics research:
What is matter made of?
How do forces work?
Where did matter come from?
ISS
Alpha Magnetic Spectrometer on the International Space Station

4. LHCb Detector Overview
Electron
Hadron
Proton beam
Goals of LHCb:
Studying the decay of B-mesons to find evidence of CP-violation
(Why is there more matter around than antimatter?)
LHCb Cross section
Vertex Locator
Muon
20 meter

5. The LHCb-VELO Detector (VErtex Locator)
Detectors and
electronics
Temperature detectors: -7ºC
Heat generation: max 1600 W
23 parallel evaporator stations
capillaries
and return hose
VELO Thermal Control System
CO2 evaporator section

6. The Velo Detector 22 August 2008 Heat producing electronics
Detection Silicon
22 August 2008
The VELO has seen particle tracks from an LHC test!
CO2 evaporator
(Stainless steel tube casted in aluminum)

7. VELO Cooling Challenges
VELO electronics must be cooled in vacuum.
Good conductive connection
Absolute leakfree
Maximum power of the electronics: 1.6 kW
Silicon sensors must stay below -7°C at all times (on or off).
To avoid thermal runaway of the irradiated silicon
Adjustable temperature for commisioning.
Maintenance free in inaccessable detector area

8. The 2-Phase Accumulator Controlled Loop (2PACL)
Long distance P7
P4-5 5
Heat out
Heat out
Condenser 6
Heat in 4
Heat in 2 3
evaporator
2-Phase Accumulator 1
Heat exchanger
Restrictor
Pump
2PACL principle ideal for detector cooling:
Liquid overflow => no mass flow control
Low vapor quality => good heat transfer
No local evaporator control, evaporator is passive in detector.
Very stable evaporator temperature control at a distance (P4-5 = P7)
Vapor
Liquid
Pressure 2 3
2-phase 4 P7 5 1 6
Enthalpy

9. VTCS Accumulator Control
Setpoint Temperature
Cooling spiral for pressure decrease
(Condensation)
Tset
Accumulator properties:
Volume: 14.2 liter (Loop 9 Liter)
Heater capacity: 1 kW
Cooler capacity: 1 kW
System charge: 12 kg liter)
System design presure: 135 bar
Pressure
Temperature
Pset
Evaporator Pressure
PID + _
Heating
Cooling
ΔPfault + _ + +
Thermo siphon heater for pressure increase
(Evaporation)
Paccumulator
Pressure drop

10. LHCb-VTCS Overview (VELO Thermal Control System)
Accessible and a friendly environment
Inaccessible and a hostile environment
2.6 m
PLC
4m thick concrete shielding wall
3.6 m
2 Evaporators
800 Watt max per detector half
2 R507A Chillers:
1 water cooled
1 air cooled
2 CO2 2PACL’s:
1 for each detector half
2 Concentric transfer lines
55 m
VELO

11. VTCS Schematics 2x CO2 2PACL’s connected to 2 R507A chillers (Redundancy) Lots of sensors and valves

12. LHCb-VTCS Cooling Components
Accumulators
VTCS Evaporator
Valves
Pumps
Condensers CO 2

13. VTCS Units Installed @ CERN
Freon Unit
CO2 Unit
July- August 2007 CO 2

14. VTCS 2PACL Operation From start-up to cold operation (1)+
2 Pump head pressure (Bar) 2
4-Accumulator liquid
level (vol %) 7
4 - Accumulator pressure (Bar) 7
5 – Evaporator
temperature (°C) 4
1 Pumped liquid temperature (°C) 1
4- Accumulator Control:
+ = Heating
- = Cooling 7 _ 7 -7 4 CO 2 7 +7 2 1
time A B C D 14
Start-up in ~2 hours

15. VTCS 2PACL Operation From start-up to cold operation (2)
Pressure B C
Accumulator
Cooling =
Pressure decrease 5
20 °C A
0 °C 2
Path of 5 4
Set-point range D
-20 °C 5 1 4
-40 °C
Enthalpy D
2 - Pump head pressure (Bar) B 2 A C 2
4 - Accumulator pressure (Bar) 5 5
5 – Evaporator
temperature (°C) 4 CO 2 4 1
1 – Pumped liquid temperature (°C) 1
time A B C D 15
Start-up in ~2 hours

16. March ’08: Commisioning of the VTCS Detector under vacuum and unpowered

17. Temperature (°C), Power (Watt), Level (vol %)
24 June ’08: After a succesful commisioning of the detector at -25°C, the setpoint is increased to -5°C. And has been running since then smoothly!
(3 sept 08) 80
Accu Heating/Cooling 60
Accu level 40
Detector half
heat load (x10) 20
Module Heat load
Temperature (°C), Power (Watt), Level (vol %)
Silicon temperature
-7°C
SP=-5°C
-20
Evaporator
temperature
SP=-25°C
-40
0:30
1:00
1:30
2:00
Time (Hour)

18. Fluctuations from the untuned chiller
VTCS performance overview for a setpoint of -5°C (Detector switched on, fully powered)
CO2 heat transfer
dT=1.4°C
Evaporator Pressure
31.15 bar = -4.18°C
Cooling block
dT=0.04°C
Cooling block temperature = -2.8°C
1 hour
dP=0.6 bar = 6.2 m static heigth
CO2 liquid temp= -42°C
Fluctuations from the untuned chiller
Detector offset from accu control: 0.7°C
CO2 liquid
dT=4.5°C
Evaporator liquid
inlet temp = -4.40°C
Evaporator vapor
outlet temp = -4.44°C
Accumulator Pressure
30.54 bar = -4.90°C

19. Summary Lessons learned
The VTCS has successfully passed the 1st commissioning phase and is ready to be used in the experiment
Operational temperature range is between 0°C and -30°C set point
It has run for 2½months continuously without any problem
It behaves very stable (<0.1°C fluctuation), with the chiller still to be tuned.
The silicon temperature is below the required -25°C set point temperature. (This is consistent with the prediction)
Lessons learned
The accumulator sometimes gives the pump a 2-phase mixture => cavitation. Problem is solved by connecting the accu to the inlet of the condenser instead of the outlet where it is now.
Operational temperature range of the evaporator is larger than expected. This is due to the “Duck Foot Cooling 1 ” principle of the transfer line.
Next time we keep the system more simple, adding redundancy is not always adding reliability………
1 The way a duck can have cold feet without loosing body heat,
by exchanging heat between the in- and outlet bloodstream.

20. Outlook The VTCS is not yet finnished, some things have to be done:
Implementing automatic back-up procedure.
Changing the accumulator connection.
Tunning the chiller.
Analyse data for publication.
Other CERN detectors (Atlas/CMS) have shown interest in the VTCS for their inner tracker upgrades.
Challenge: Scaling of the 1.6kW VTCS to a 100kW system.
Bigger chalenge: Convince a few hundred physists to do so.
Construction of a mini desktop 2PACL CO2 circulator for general purpose laboratory use.