CryogenicsCryogenics forfor LiquidLiquid ArgonArgon CalorimetersCalorimeters

Caroline Fabre

on behalf of the ATLAS Liquid Argon Cryogenics Collaboration

AT-ECR/C.Fabre May 31, 2007 Cryogenics for Liquid Argon Calorimeters

CONTENTS:

1. The ATLAS liquid argon calorimeters

2. Main requirements for the associated cryogenic system

3. The LAr cryogenic system:

adopted solutions

and results

4. Special features

5. Conclusion

AT-ECR/C.Fabre May 31, 2007 The ATLAS Liquid Argon Calorimeters (1)

9 Barrel Calorimeter:

ƒ D: 4.3 m; L:6.5 m ƒ Weight: 120 t ƒ Argon volume: 40 m3

Electromagnetic barrel half-wheel

AT-ECR/C.Fabre May 31, 2007 The ATLAS Liquid Argon Calorimeters (2)

9 End-cap Calorimeter: ƒ D: 4.3 m; L: 3 m ƒ Weight: 219 t ƒ Ar volume: 19 m3

Calorimeters are highly complicated composite structures made of copper, lead, stainless-steel and glass-epoxy… placed in aluminium cryostats

AT-ECR/C.Fabre May 31, 2007 Main Cooling Requirements

9 Cool-down criteria:

∆T must be kept within strict limits to avoid excessive stresses or displacements

In total: 7 criteria defined for the barrel

11 criteria defined for the end-cap (T dependence)

9 Steady-state requirements:

ƒ No gas bubble formation

ƒ Liquid argon bath temperature constant at about 88.4 K Energy measurement sensitivity: 2 % per K ƒ Temperature gradient across bath < 0.7 K

ƒ Argon purity < 2 ppmv of O2-equivalent

AT-ECR/C.Fabre May 31, 2007 The LAr Cryogenic System (1)

2001-2005: 9 Project stages: Cryostat and detector integration 1997-2004: Individual cryogenic Cold performance test test, at operating and calibration in particle beam temperature of the 128 individual detector modules of the 3 calorimeters

Sept. 2005: Transport of an end-cap calorimeter Nov. 2004: towards Point 1 Barrel lowering in ATLAS pit AT-ECR/C.Fabre May 31, 2007 The LAr Cryogenic System (2)

3 2x50m LN2 storage tanks 3 1x80m GN2 Buffer

1.3 km interconnecting 20kW@84K LAr & LN2 transfer-lines N2 refrigerator

3 15m N2 Phase Separator Dewar

11 distribution valve boxes 2x50m3 LAr storage tanks

(picture J.Metselaar) AT-ECR/C.Fabre May 31, 2007 The LAr Cryogenic System / Solutions (3)

9 Procedures during cool-down: 1. Rinsing cycles

2. Gas cooling: forced convection of GN2 in heat exchangers inlet T decreased on a ramp

3. Liquid cooling: circulation of vaporizing LN2 LN2 4. Condensing of argon tank Expansion vessel 1.25 bar

2.1 Cool-down rate bar LN2 phase limited by an 5.3 separator interlock bar triggered by the cooling criteria

End-cap Barrel LN2 End-Caps pump LAr Tanks

AT-ECR/C.Fabre May 31, 2007 The LAr Cryogenic System / Solutions (4)

Ar and N saturation curves 9 Steady 2 state: (End-Cap A)

Steady state 2.9

Pmin N2 = 2.1 bar 7 K

3.5 K

1.25

Ar triple point T = 83.8 K P = 0.69 bar

88.3 89.3 87.5

AT-ECR/C.Fabre May 31, 2007 The LAr Cryogenic System / Results (5)

Barrel mean temperature and ∆T variation during cool-down 300 20

280 - heat extracted during cool-down: 6.9 GJ 18 - heat load to the cryostat: 1.9 kW 260 16 240 14 220 12 200 Average cooling rate 10 0.22 K/h T (K)

180 ∆ Cryostat 8 160 filling Mean temperature (K) temperature Mean 6 140 & Sub-cooling 120 4

100 2 88.4 80 0 0 10203040Time (Days)

From 295K to 140K : Between 140K and 100K: From 100K to 90K:

GN2 cooling LN2 cooling Argon condensing

AT-ECR/C.Fabre May 31, 2007 The LAr Cryogenic System / Results (6)

End-cap A mean temperature and ∆T variation during cool-down 300 30 - heat extracted during cool-down: 15.7 GJ 28 280 - heat load to the cryostat: 2.1 kW 26 260 24 240 22 20 220 18 200 16 T (K)

180 14 ∆ Cryostat 12 160 filling 10 Mean temperature (K) temperature Mean & 140 Average cooling rate 8 0.13 K/h Sub-cooling 120 6 4 100 88.3 2 80 0 0 1020304050607080Time (Days)

Between 100K From 295K to 125K : Between 125K and 100K: Purges and 90K: GN cooling LN cooling 2 2 Argon condensing AT-ECR/C.Fabre May 31, 2007 The LAr Cryogenic System / Results (7)

9 Steady state:

ƒ Temperature uniformity: < 0.3 K

ƒ Temperature stability: < 0.02 K

ƒ LAr bath sub-cooled with 4.2 K to 7.7 K

ƒ Argon purity: between 0.1 and 0.3 ppm of O2-equivalent

(Barrel)

0.07 K drop due to change in LN2 pressure

Detector temperature stability: < 0.02 K (plot P.Puzo)

AT-ECR/C.Fabre May 31, 2007 Uninterrupted Functioning over 15 Years (1)

9 12 meter longitudinal movement of the end-cap cryostats : Cryogenic lines between expansion vessel and cryostat designed to follow Transfer-line supplying LN to the heat exchangers 2 this movement Signal cables and compressed air pipes Inner diameter: DN150 LAr expansion Outer diameter: DN300 vessels Length: 35 m Bending radius: 1.5 m

12 m displacement

End-cap C

LN2 heat exchangers LAr flexible line between expansion vessel and cryostat regulation valve boxes End-cap A and associated(picture P displacement.Petit) system

AT-ECR/C.Fabre May 31, 2007 Uninterrupted Functioning over 15 Years (2)

First displacements of end-cap A to its extreme opening position with all services connected: 9 cold & empty on 17-02-2007 9 filled with LAr on 21-05-2007

© Copyright CERN

AT-ECR/C.Fabre May 31, 2007 Uninterrupted Functioning over 15 Years (3)

9 Redundancies :

ƒ LN2 pumps (x3)

ƒ LN2 supply services (x3) ƒ all essential devices on backed-up electrical power system: -EDF/EOS network 2x 3 - diesel generators 50 m

Expansion vessel LN2 -UPS 1.25 bar tanks ƒ compressed air and cooling water

backed up 15 m3 Refri-

LN2 gerator 5.3 PSD bar 20kW @84K

End-cap Barrel LNLN22pump End-Caps pump LAr Tanks

AT-ECR/C.Fabre May 31, 2007 Safety Aspects

9 Special features related to safe handling of large volume of cryogenic liquids in underground area

ƒ Argon volume of the three cryostats can be emptied into 2 x 50 m3 argon storage tanks by: -gravity -cryogenic pump ƒ Argon tanks are:

- equipped with LN2 condenser and kept cold - entirely made of stainless steel ƒ Items containing large volumes are:

- equipped with safety valves collected to a dedicated DN 500 pipe going to surface - placed above retention pits ƒ Gas constantly renewed from the retention pits by surface extraction system ƒ Insulation vacuum levels are monitored ƒ Oxygen detectors AT-ECR/C.Fabre May 31, 2007 Conclusion

9 Barrel and End-Cap A successfully cooled-down in 2006 and in stable situation for respectively 10 and 3 months:

Argon bath purity, temperature homogeneity and stability fully satisfactory for detector operation purposes

9 End-Cap C cold, to be filled mid- June:

All three calorimeters fully Barrel Calorimeter in operation in its final position encircled by BT Magnets, Tile Calorimeter and operational from July onwards © COPYRIGHTMuon CERN Chambers

This achievement is the result of collaboration between: BNL, CEA, CERN, LAL, LPSC and NTNU

AT-ECR/C.Fabre May 31, 2007