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Transients scenarios for the cryogenic operation of superconducting magnets of LHC experiments

Transients scenarios for the cryogenic operation of superconducting magnets of LHC experiments. Experience at CERN R.Pengo CERN, AT-ECR. Content of the presentation. Details for CMS and ATLAS of: cooling down process static heat load dynamic heat load fast discharge of the magnets

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Transients scenarios for the cryogenic operation of superconducting magnets of LHC experiments

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  1. Transients scenarios for the cryogenic operation of superconducting magnets of LHC experiments Experience at CERN R.Pengo CERN, AT-ECR

  2. Content of the presentation • Details for CMS and ATLAS of: • cooling down process • static heat load • dynamic heat load • fast discharge of the magnets • recovery after a fast dump

  3. Structure of the s/c magnets • CMS is composed of • a s/c solenoid, divided in 5 sectors • ATLAS is composed of • a s/c Central Solenoid (CS) • a Barrel Toroid (BT), formed by 8 s/c race-track coils • 2 End Cap Toroids (ECT), each formed by 8 s/c squared coils

  4. Cooling methods for CMS & ATLAS • CMS • The solenoid is indirectly cooled by LHe, driven by thermosyphon movement (i.e. gravity driven) • ATLAS • The CS is indirectly cooled either by the JT circuit of the Main Refrigerator (MR) or by thermosyphon movement • Both BT and ECT’s coils are indirectly cooled by forced LHe flow produced by a 1.2 kg/s centrifugal pump

  5. Cold Mass Inventory • CMS total cold mass is 220 Tons (cylinder 6.6 m x 12.5 m) • ATLAS total cold mass is ca. 700 Tons • CS ca. 6 Tons (cylinder 2.5m x 5.3m) • BT (340 +20) Tons (8: 25 m x 5 m) • ECT’s (2 x 160) Tons (8: 5m x 5m)

  6. Where we are with the commissioning • Actual status: • CMS fully tested on the surface • ATLAS • CS fully tested (surface and cavern) • BT fully tested (surface and cavern) • ECT-A tested at LN2 temperature on surface • ECT-C under test on the surface

  7. Cooling down of the Magnets

  8. Cooling down of the Magnets • CMS 1.2 kW @ 4.5 K Refrigerator used DT< 22K 10 days Cooling Time ca. 22 days

  9. Cooling down of the Magnets • ATLAS :CS • Shield Refrigerator (SR) & Main Refrigerator (MR) used 4 days • SR for shield • MR for CM SR: Cold Mass and shield in series 75 K

  10. Cooling down of the Magnets • ATLAS :BT • Shield Refrigerator (SR) & Main Refrigerator (MR) used 10 days Start of the 1.2 kg/s LHe pump • SR for the shields • MR for Cold mass SR: cold mass and shield in parallel

  11. Cooling down of the Magnets • ATLAS :BT • Shield Refrigerator (SR) & Main Refrigerator (MR) used DT< 40 K

  12. Cooling down of the Magnets • ATLAS : ECT-A 10 Days Only LN2 precooler used

  13. Cooling down of the Magnets • ATLAS : ECT-C (in progress) 10 days

  14. STATIC HEAT LOAD

  15. STATIC HEAT LOAD • CMS • Measured by LHe level decreasing in Phase Separator • Natural Temperature increasing on the cold mass

  16. STATIC HEAT LOAD Débit AdI 2 x 0,4 g/s Dniv(A-B) = 6,75% en 10’= Soit 277 l/h Bilan = 254 l/h = 178 W A B • CMS: Measured by LHe level decreasing in Phase Separator (178 W) LHe level in Phase Separator From Ph. Bredy, CEA Saclay

  17. STATIC HEAT LOAD • CMS: Natural Temperature increasing of the cold mass (174 W) Cold mass bilan : NbTi 4.9 t Cu 8.6 t Al pur 73.9 t Al renf 6082 90.4 t G10 9.9 t Al cyl 5083 34.8 t 10 K •  2 K/ 21 ½ min = 154 W on Cold mass alone • (SdP heat loads to be added 20 W) • Total = 174 W CDS synchronization ! 5 K From Ph. Bredy, CEA Saclay

  18. STATIC HEAT LOAD • ATLAS: CS • Measurement of total loss was done during thermosyphonoperation mode with disconnected refrigerator and looking at the level/time change in the control dewar Results: - 17 Watts for the solenoid and the chimney; - below 10 Watts for the dewar.

  19. STATIC HEAT LOAD • ATLAS: Barrel Toroid CM • For each of the 8 race-track coils the heat load has been measured • in the surface test hall (Mass-flow meter) • in the UX15 cavern after assembling into BT (natural temperature increase) • The total heat load of the BT has been also measured in the cavern

  20. STATIC HEAT LOAD • ATLAS: Barrel Toroid Tmax, Tmin on coils Tin-Tout on the pipes Pt1000 Carbon resistors

  21. STATIC HEAT LOAD • ATLAS: Barrel Toroid Values measured in test station TOTAL MEASURED IN TEST STATION 571 W TOTAL IN UX15 IS 586 W

  22. STATIC HEAT LOAD • ATLAS: Barrel Toroid LHe Pumps: 660 W PCS+TL11+Cryoring: 250 W BT: 620 W (or 1530-660-250)W

  23. STATIC HEAT LOAD • ATLAS: Barrel Toroid Shields • For each of the 8 cryostats • in the surface test hall (Mass-flow meter) • Average 800 W • the total heat load of the BT shield has been also measured in the cavern (Mass-flow meter) • Total 6000 W

  24. DYNAMIC HEAT LOAD

  25. DYNAMIC HEAT LOAD • Flux is proportional to Current: • Φ = L x I , V = -dΦ /dt = - L x dI/dt • Voltage is induced when changing current • And energy is dissipated by the induced current on the casing (~ autotransformer) Al Coil casing 2 x 60 = 120 turns

  26. DYNAMIC HEAT LOAD • ATLAS: Calculated: No Fit! Slow dump equivalent One coil: L = 0.5667 H, Total BT: L= 5.5 H => expected value 350 W

  27. DYNAMIC HEAT LOAD • ATLAS: BT Level of LHe is reduced due to the higher vaporization during slow discharge

  28. DYNAMIC HEAT LOAD • ATLAS: BT LHe vapor mass flow on the phase separator is increased due to the higher heat load ~380 W

  29. DYNAMIC HEAT LOAD • ATLAS: CS • Eddy current loss are around 25 Watts. • Measurement principle: • compare consumption during ramp up at 6 A/s with previously measured static losses by looking at the heater power in the control dewar which is reduced by 25 watts. • Furthermore “gas counting”.

  30. DYNAMIC HEAT LOAD • CMS: 7.5 K Current decreasing during slow discharge Thermosyphon Mass flow is naturally increased due to the higher heat load 4.5 K Temperature increase ~ 0.28 K

  31. DYNAMIC HEAT LOAD • CMS Temperature increase ~ 0.28 K Fast discharge at 5000 A Slow discharge

  32. FAST CURRENT DISCHARGE

  33. FAST CURRENT DISCHARGE • CMS: stored EM energy is 2.5 GJ (about 220 Tons) Temperature rise up to 70 K 1 hour Pressure rise in PS

  34. FAST CURRENT DISCHARGE • ATLAS-CS: Stored EM energy is 40 MJ 1 min

  35. FAST CURRENT DISCHARGE • ATLAS-CS: pressure rise Current: 7800 A Coil return: max 7.11 bar Coil inlet: max 4.32 bar From F.Haug

  36. FAST CURRENT DISCHARGE • ATLAS-BT: Stored EM vs. Enthalpy EM Energy at Current [A] 57 K BT Enthalpy

  37. FAST CURRENT DISCHARGE • ATLAS-BT: 15 min Pressure in Phase Separator Pressure on the return to the Shield Refrigerator

  38. FAST CURRENT DISCHARGE • ATLAS-BT:

  39. FAST CURRENT DISCHARGE • BT: Recovery after a full current fast dump One day 58 K

  40. SummaryData on transient modes of operation have been displayed and discussed, namely:- cooling down process- static heat load- dynamic heat load- fast discharge of the magnets- recovery after a fast dump. The results are in good agreement with the design

  41. I would like to thank for their collaboration all colleagues from CERN and from the external Institutes involved (CEA-SACLAY,INFN,KEK,RAL)

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