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The challenges for getting the nominal cryogenic conditions

The challenges for getting the nominal cryogenic conditions. L. Tavian, AT.CRG – CERN – 14 May 2008. Contents. Introduction to LHC cryogenic system (layout, architecture) Preparation before cool-down (Purge, flushing)

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The challenges for getting the nominal cryogenic conditions

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  1. The challenges for getting the nominal cryogenic conditions L. Tavian, AT.CRG – CERN – 14 May 2008

  2. Contents • Introduction to LHC cryogenic system (layout, architecture) • Preparation before cool-down (Purge, flushing) • Transient operations to reach nominal operating condition (Cool-down, filling) • Tuning of the cryogenic system: • With an without electrical circuit powering • Coping with resistive transition • Availability for powering • Conclusion L. Tavian - LHC Cryogenics

  3. Introduction Main cryogenic requirement: Cooling of 24 km of superconducting magnets @ 1.9 K, 8.33 T L. Tavian – LHC Cryogenics

  4. Why 1.9 K ? With Nb-Ti as technical superconductor, to get sufficient current density above 9 T, cooling below 2 K is required Trade-off between magnet and cryogenic complexity L. Tavian – LHC Cryogenics

  5. Why helium as refrigerant ? Helium is the only available cryogen which is not solid below 15 K L. Tavian – LHC Cryogenics

  6. 5 cryogenic islands 8 helium cryogenic plants: 1 plant serves 1 sector (18 kW @ 4.5 K, 2.4 kW @ 1.8 K and 600 kW LN2 precooler) Cryogenic system layout (Distribution line) (Interconnection box) Cryogenic plant L. Tavian – LHC Cryogenics

  7. Cryogenic architecture L. Tavian – LHC Cryogenics

  8. Typical even-point architecture L. Tavian – LHC Cryogenics

  9. Photo gallery: Refrigerators 1.8 K refrigeration units (2.4 kW @ 1.8 K) 4.5 K Refrigerators (18 kW @ 4.5 K) L. Tavian – LHC Cryogenics

  10. Photo gallery: Storage and distribution Vertical transfer line GHe storage LN2 storage Cryo-magnet Distribution line (QRL) Interconnection box L. Tavian – LHC Cryogenics

  11. Superfluid helium cooling principle Principle of the LHC He II Cooling Scheme • Heat exchanger tube in copper with a diameter DN50. • Overall thermal conductance: ~ 100 W/m.K • (i.e., for 1W/m, a temperature difference of 10 mK) L. Tavian – LHC Cryogenics

  12. Normal operating conditions L. Tavian – LHC Cryogenics

  13. Magnet-cell (107 m) cooling scheme 107 m L. Tavian – LHC Cryogenics

  14. Other tunnel equipments Inner triplet RF cavities (P4) Standalone magnet Feed box (DFB) Standard cell (107 m) L. Tavian – LHC Cryogenics

  15. Contents • Introduction to LHC cryogenic system (layout, architecture) • Preparation before cool-down (Purge, flushing) • Transient operations to reach nominal operating condition (Cool-down, filling) • Tuning of the cryogenic system: • With an without electrical circuit powering • Coping with resistive transition • Availability for powering • Conclusion L. Tavian - LHC Cryogenics

  16. Sector preparation: Purge & leak test • Removal of air in circuit by evacuation and He filling: • 400 m3 of circuits distributed over 3.3 km, • He taken from medium pressure storage, • at least 3 cycles to get air and humidity content below 50 ppm to be compatible with the cryoplant purification system (dryer and adsorber), • 1 to 2 cycles per day, • ~10 kCHF of He per sector purge. L. Tavian – LHC Cryogenics

  17. Sector preparation: circuit flushing • Removal of dust and debris by flushing the helium circuits with high helium flow at 300 K: • all circuits flushed in series, • QRL headers first to avoid migration of dust to the machine circuits (magnets and beam screens), • use of refrigerator compressors for flow production, • the complete return flow is passing trough a filterto stop the debris, • 1 to 2 week per sector depending of the circuit cleanliness. L. Tavian – LHC Cryogenics

  18. Filter inspection after flushing Foam (welding plug) Debris & Kapton Dust Possible short in magnet diodes Travellers But the sooner the best ! L. Tavian – LHC Cryogenics

  19. Contents • Introduction to LHC cryogenic system (layout, architecture) • Preparation before cool-down (Purge, flushing) • Transient operations to reach nominal operating condition (Cool-down, filling) • Tuning of the cryogenic system: • With an without electrical circuit powering • Coping with resistive transition • Availability for powering • Conclusion L. Tavian - LHC Cryogenics

  20. 300 – 5 K cool-down of Sector • Cool-down of 4625 t per sector over 3.3 km: • From 300 to 80 K: 600 kW pre-cooling with LN2, • up to ~5 t/h, • 6 LN2 trailer per day during 10 days (1250 t of LN2 in total); LN2 logistics critical. • From 80 to 5 K: Cryoplant turbo-expander cooling, • cryoplant tuning critical (4 different types). • LHe filling: 15 t of LHe in total (4 trailers). • Up to 40 PID loops to control the cool-down speed of the cells, standalone magnet and DFB. L. Tavian – LHC Cryogenics

  21. Logitics during sector cool-down Unloading of LHe & LN2: ~ 200 kCHF of LN2 per sector cool-down, ~ 600 kCHF of LHe per sector filling. L. Tavian – LHC Cryogenics

  22. 300-5 K cool-down time (w/o filling) • Cool-down time hampered by: • external factors (leaks, electrical short-circuits, electrical control plateaus), • cryogenic stops (utility loss, cryogenic problems), • cryogen logistics management (week-ends, nights…), • cryoplant and tunnel cooling loops tuning and limitations. Total w/o external factors & cryoplant stops Room for improvement ! L. Tavian – LHC Cryogenics

  23. Filling & cool-down to 1.9 K • LHe filling and cool-down completion by using the 1.8 K refrigeration unit • Complex operation of cold compressors (up to 4 in series) • Filling and cooling of electrical feed boxes and their current leads (as well as RF cavity modules, if any) • 1 week per sector Cold compressors L. Tavian – LHC Cryogenics

  24. Cold compressors Definition of reduced parameters: and m: mass-flow Tin: Inlet temperature Pin: Inlet pressure N: Rotational speed Subscript 0: Design condition Complex operation of hydro-dynamic compressor: - high rotational speed: up to 800 Hz, - reduced operation range at constant pressure ratio. L. Tavian – LHC Cryogenics

  25. Contents • Introduction to LHC cryogenic system (layout, architecture) • Preparation before cool-down (Purge, flushing) • Transient operations to reach nominal operating condition (Cool-down, filling) • Tuning of the cryogenic system: • With an without electrical circuit powering • Coping with resistive transition • Availability for powering • Conclusion L. Tavian - LHC Cryogenics

  26. Tuning of the cryogenic system • Commissioning at cold of instrumentation (temperature, cryo-heaters, Lhe level, valves) • Commissioning of sub-systems like electrical feed boxes and superconducting links which are cold tested for the first time in the tunnel • Tuning of the control loops to get the required stability and conditions for allowing the magnet powering • Validate the conformity of the equipment cooling • 1 to 2 weeks partially in parallel with the last cold-down phase L. Tavian – LHC Cryogenics

  27. Commissioning of instrumentation *: including some redundant sensors installed but not connected Always on-line with the instrumentation database L. Tavian – LHC Cryogenics

  28. CRYO Instrumentation expert tool PVSS DS Return Module PLC QUIC Schneider PLC S7-400 Siemens FECs (FESA) RM sector 81 UNICOS RM sector 78 RM sector 78 Commissioning of the control system Local Cryogenic control room Central Control Room PVSS DS Sector OWS [1..x] OWS [1..x] WFIP Networks (7) PROFIBUS DP networks PROFIBUS PA networks RadTol electronics Courtesy E. Blanco TT, PT, LT, DI, EH CV L. Tavian – LHC Cryogenics

  29. Commissioning of sub-systems • DFB commissioning : Level measurement and current lead temperature control and stability • ~ 1 week per sector L. Tavian – LHC Cryogenics

  30. Tuning of control loops Tuning of all control loops and the corresponding control logic to get the required stability and conditions for allowing first the ELQA activity and then the magnet powering L. Tavian – LHC Cryogenics

  31. Validation of cooling conformity • Fill-up and boil-off of standalone magnets to confirm the level and the complete wetting of the magnet coils with liquid helium. • Validation of the conformity of the cooling circuits: • Non conformities identified in some feeding pipes of the 1.8 K bayonet heat exchangers. Use of the built-in redundancy to cool the non-conforming cells. L. Tavian – LHC Cryogenics

  32. Boil-off of standalone magnets 14 May 2008 L. Tavian – LHC Cryogenics 32

  33. Slope Cooling loop redundancy L. Tavian – LHC Cryogenics

  34. S5-6 magnet temperature stability ~ 140 temperature measurements superimposed ! (Validation of the thermometry quality) L. Tavian - LHC Cryogenics

  35. Contents • Introduction to LHC cryogenic system (layout, architecture) • Preparation before cool-down (Purge, flushing) • Transient operations to reach nominal operating condition (Cool-down, filling) • Tuning of the cryogenic system: • With an without electrical circuit powering • Coping with resistive transition • Availability for powering • Conclusion L. Tavian - LHC Cryogenics

  36. Quench recovery Quench relief valve Recovery time: 6 h Recovery time: 4.5 h L. Tavian – LHC Cryogenics

  37. Contents • Introduction to LHC cryogenic system (layout, architecture) • Preparation before cool-down (Purge, flushing) • Transient operations to reach nominal operating condition (Cool-down, filling) • Tuning of the cryogenic system: • With an without electrical circuit powering • Coping with resistive transition • Availability for powering • Conclusion L. Tavian - LHC Cryogenics

  38. Cryo-availability BC HWC (Considering independent origins of problems) • Availability for sector HWC : 80 % during weeks w/o resistive transition • To be improved during beam commissioning: more than 95 % per sector Note : A cryogenic system takes time (hours) to recover any kind of stop ! L. Tavian – LHC Cryogenics

  39. Contents • Introduction to LHC cryogenic system (layout, architecture) • Preparation before cool-down (Purge, flushing) • Transient operations to reach nominal operating condition (Cool-down, filling) • Tuning of the cryogenic system: • With an without electrical circuit powering • Coping with resistive transition • Availability for powering • Conclusion L. Tavian - LHC Cryogenics

  40. Conclusion • Time for getting nominal conditions: • Presently 10 weeks for getting nominal conditions, • In routine operation, about 1 month is foreseen, • LHC cryogenics is the largest, the longest and the most complex cryogenic system worldwide. • Operation for the needs of Sector HWC is now demonstrated. • Based on experience, together with procedures and tools being put in place, availability must be improved for the next phase: The Beam Commissioning. L. Tavian - LHC Cryogenics

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