OPERATIONAL EXPERIENCE ON CRYOGENIC SYSTEMS FOR LARGE-SCALE ACCELERATORS AT CERN

Transcription

1 OPERATIONAL EXPERIENCE ON CRYOGENIC SYSTEMS FOR LARGE-SCALE ACCELERATORS AT CERN S. CLAUDET, M. SANMARTI, L. SERIO, L. TAVIAN 1 st Workshop on Cryogenics Operations Jefferson Laboratory - Newport News US - March,

2 Introduction LEP cryogenics Overview Operational experience LHC cryogenics Overview Operational experience LHC cryogenics future operation Contents 2

3 Cryogenic Refrigeration Capacity at CERN LHC ATLAS, CMS K LEP2 LEP OMEGA, BEBC ISR Low-Beta ALEPH, DELPHI, LEP Low-Beta Year The largest helium liquefaction center in the world! Courtesy of Ph. Lebrun 3

4 C.O.P. of Large Cryogenic Helium Refrigerators 500 C.O.P. 4.5K] Carnot 0 TORE SUPRA RHIC TRISTAN CEBAF HERA LEP LHC Courtesy of Ph. Lebrun 4

5 Transport of Refrigeration in Large Distributed Cryogenic systems 0.5 Temperature difference [K] Tevatron LEP2 Tore Supra Pressurised He II Saturated LHe II He I UNK HERA TESLA SSC (HEB) SSC (main Ring) Distance [km] LHC Courtesy of Ph. Lebrun 5

6 Thermodynamic States of He in CERN accelerators P [kpa] SOLID HeII Arc Magnets Special Magnets RF Cavities HeI CRITICAL PT Beam Screens HTS Part of Current Leads Thermal Shields Resistive Part of Current Leads 10 GAS 1 Heat Exchanger Tubes 1 10 T [K] LEP LHC Courtesy of Ph. Lebrun 6

7 He Inventory of Large Cryogenic Systems Virtual Liquid 2 MPa LOSSES %inventory/yr Utility stops 30 Operation 15 Purge/conditioning 5 TOT losses 50 [tonnes] 150 7% 5% Total LHC inventory: 96 tonnes of He % 60% Cold masses Header C Other headers Cryoplants 0 Tevatron HERA CEBAF RHIC LEP2 LHC (SSC) 7

8 Introduction LEP cryogenics Overview Operational experience LHC cryogenics Overview Operational experience LHC cryogenics future operation 8

9 Introduction Cryogenics for LEP2 accelerator Point 4 Point SCQ Modules installed and 4 SCQ SCQ 20 LEP operation since 1989 Installation of SC cavity modules and cryoplants from 1992 Four 12/ K: Storage tanks, compressor station, upper cold box ( K) Lower cold box and distribution lines ( m) Point 2 Point 8 9

10 LEP2 Cryogenic system progress Running hours [h] IP8 IP6 IP4 IP2 IP2-6kW Operation & Maintenance Contract Results Oriented Upgrade 12 kw to 18 kw

11 Cryogenics vs. LEP2 Project (Power balance) Equiv. cooling power [kw] Cryo Upgrade Nb of modules & beam energy [GeV] shielding Static load Dynamic load liquefaction load Nb Modules LEP Energy Total heat load Available Power Thermal Shield 2 kw/cryoplant Static losses 27 W/module 80W/TL & val. Dynamic losses (RF field)^2/qf Liquefaction 0.8g/s x module 11

12 Exploitation Team Person-year Staff Evolution APT Staff (LEP2) 1 Eng. & 4 Oper. 6 person-year Maint. 1 person-year Manag. CERN Staff Contract monitoring Technical assistance Interfaces with LEP APT Staff CERN Staff Total 12

13 Operation Performance & statistics More than h accumulated. Cryo avg. failure downtime: Downtime rate [%] Cryogenic system downtime rates from 1996 to 2000 Cryo failures rate Utility failures rate De-icing LEP impact Cryo Upgrade per 1000 h. of LEP operation (0.7 %) Utility failures downtime:1.5 % De-icing: reduced cooling capacity. Time used for machine develop.

14 High reliability of LEP2 cryogenic system Preventive maintenance and fast repair during operation Up-to-date documentation and well-trained operators Influence of the circulating beam Bunch length sensitivity and proportional to beam current^2 High losses in RF antenna cables (cooling modified) Thermoacustical Oscillations: outlet transfer line Cryogenic Issues for LEP Machine Turbine filter clogging: reduction of cooling capacity available and risk of filter destruction (after upgrade) 1st and 2nd turbine filters at 120 and 90 K respectively H2O and CO2 traces respectively (spectroscopy) Periodic de-icing (warm up and cleaning) Duration (6-10 hours) & scheduling in collaboration with LEP Design weakness Buckled bellow in vertical transfer line, plate-fin heat exchanger Upgraded turbines and oil separation system Major technical problems after maintenance shutdowns (after restart) Twice for motor bearings, once for a compressor (out of 24) Fixing structures of compressors skids to the floor Aging of components (starting from hours) Compressors oil injection piping, oil pumps, air and He leaks

15 Introduction LEP cryogenics Overview Operational experience LHC cryogenics Overview Operational experience LHC cryogenics future operation 15

16 LHC Parameters (p-p) impacting on Cryogenics Circumference 26.7 km Beam energy in collision 7 TeV Beam energy at injection 0.45 TeV Dipole field at 7 TeV 8.33 T Luminosity cm -2.s -1 Beam intensity 0.56 A Energy loss per turn 6.7 kev Critical energy of radiated photons 44.1 ev Synchrotron power per beam 3.8 kw Stored energy per beam 350 MJ Operating temperature 1.9 K Cold mass 36.8x10 6 kg Helium inventory 96x10 3 kg 16

17 Basic Duties of the LHC Cryogenic System Maintain all magnets below 1.9 K in normal operation Cool-down and fill (respectively empty and warm-up) a machine sector in less than 2 weeks Accommodate resistive transitions of full cells and recover from them in few hours Additional Allow rapid cool-down and warm-up of limited-length strings for repair or exchange of magnet Accommodate generalized resistive transition of a sector without helium loss 17

18 Constraints of the LHC Cryogenic System Existing LEP tunnel 3.8 m diameter (in arcs) 3.3 km-long sectors deep underground with limited access shafts and technical service areas 1.4 % slope and elevation differences suburban and rural region Reuse of LEP cryogenic infrastructure 4 helium refrigerators of K, upgraded to 18 kw piping and storage vessels 18

19 Overview of the cryogenic system 1/2 (distribution line) (interconnection box) 5 cryogenic islands 8 refrigerators 2 at P4, 6 and 8, 1 at P2 1 at P1.8 1 refrigerator serves 1 sector ( K, 600 kw precooler) possibility to couple two refrigerators via the interconnection box 2 refrigerators for 1 sector 19

20 Overview of the cryogenic system 2/2 Odd point MP Storage Even point MP Storage Odd point MP Storage 1.8 K Refrigeration Unit Warm Compressor Station New 4.5 K Refrigerator Warm Compressor Station Cold Box Existing 4.5 K Refrigerator Warm Compressor Station Upper Cold Box 1.8 K Refrigeration Unit Warm Compressor Station Shaft Surface Cold Compressor box Lower Cold Box Interconnection Box Cold Compressor box Cavern Distribution Line Magnet Cryostats, DFB, ACS LHC Sector (3.3 km) Distribution Line Magnet Cryostats, DFB, ACS LHC Sector (3.3 km) Tunnel 20

21 Warm Compressor Station of K Cryoplant (Power Input ~4 MW) 21

22 LHC K Cold Box K to 75 K K to 20 K 41 g/s liquefaction 1 st in operation since hours Availability: Reduced capacity 99 % Full capacity ~80 % hours on-call intervention 5700 hours Availability: 99.4 % 190 h on-call intervention (3.3 %) Major consolidations motor-compressors skids oil injection valves shaft seal lubrication Turbine bearing and brake regulation He-N2 precooler HX

23 LHC K Cold Box K to 75 K K to 20 K 41 g/s liquefaction 1 st in operation since end hours Major consolidations motorcompressors skids oil injection valves shaft seal lubrication Verification of N2 precooler HX capacity 23

24 Specification of LHC 1.8 K Refrigeration Units 1.8 K Refrigeration Unit CCB WCS Cold compressors B Adsorbers Turblne D C 4.5 K Refrigerator LHC Sector Load 0.13 MPa, K 0.3 MPa 4.6 K Steady state operation modes: Installed pumping capacity 125 g/s at 15 mbar (i.e. ~ K) Turndown capability: 1 to 3 without extra liquid burning Cold return temperature to the 4.5 K refrigerator below 30 K (reduced capacity) to 20 K (installed capacity). Capacity check in standalone mode (Interface B closed) LHe 1.8 K Q 1.8K 24

25 Cold Compressor Boxes of 1.8 K Refrigeration Units IHI-Linde Cold Compressor box Air Liquide Cold Compressor box 25

26 1.8 K refrigerators measured performances 140 Magnet ramp-up Mass Flow Tolerance 0 Set-Point AL - Inlet Pressure IHI-Li Inlet Pressure Physics Time (min) Beam abort Inlet Pressure (mbar) IHI - Linde : ± 2.2 mbar... Air Liquide : ±0.3 mbar! 26

27 LHC Cryogenic Components in Tunnel 27

28 28

29 LHC Magnet Test String String K 172 quench 15 thermal cycles 3275 electrical cycles String K Availability: 97.3 % 3 thermal cycle 42 quenches 130 h on-call intervention (1.6 %) 29

30 Typical LHC ramp to nominal current (11860 A) [K] 2 Validation of performance and sizing rules of the bayonet heat exchanger for transporting linear heat loads in the W/m range [ka], W/m Verification of budgeted heat loads (20.4 W) within the precision of measurement (+/- 1.9 W) W/m 0.3 W/m nohm :50 11:00 11:10 11:20 11:30 11:40 30

31 Introduction LEP cryogenics Overview Operational experience LHC cryogenics Overview Operational experience LHC cryogenics future operation 31

32 4 Control Rooms: (2) accelerators (1) techn. services (1) cryogenics What is controlled: Accelerators Transfer lines Exp areas Access systems Electricity Cooling Vacuum Cryogenics 32

33 Integrate the all operation functions into ONE CERN Control Centre: the CCC. Manned with 12 operators on 3x8 shift. 3 operators dedicated to Cryogenics 2 operators on-call Maintenance activities outsourced to external firm(s) 33

34 LHC commissioning/operation planning P5 P4 P6 Legend: QRL QUI Refrigerator Arc Dispersion Suppressors Long Staight Section ee e B e S iii i dd dd nn nn oo o tt t cc g n ~ r r r r c r a m k P3 P7 Injection test Operation P2 Commissioning P1 P8 P1.8 34

35 LEP2 cryogenic system has shown high reliability and remarkable operation performance with carefully planned maintenance and periodic checks up-to-date documentation and well-trained operators Conclusions Operation/maintenance can be successfully outsourced but requires: commissioning and first years operation by the staff that designed it It could be a long adaptation process minimum staff dedicated to upgrades, consolidations, monitoring and interface with other accelerator systems The LHC cryogenic system basic design criteria, main choices and functionalities have been successfully tested Plants and equipments are being installed, commissioned and are progressively going into operation 35

36 Conclusions SUMMER