1. OLAV III Experience with the LHC Insulation Vacuum System S. Blanchard, P. Cruikshank, B. Jenninger, N. Kos, W. Maan, L. Mourier, N. Provot, J. Wallner 11th July 2011OLAV III; Session 21

2. Contents Introduction to the LHC insulation vacuum system Experience with permanently installed 300 l/s turbomolecular pumping stations Pressure monitoring Leak tightness Discussion points 11th July 2011OLAV III; Session 22

3. LHC insulation vacuum system QRL & Magnet insulation vacuum system – Continuous arc cryostat subdivided into insulation vacuum subsectors or volumes: 112 magnet and 72 QRL insulation vacuum subsectors ~ 80 m 3 (214 m magnets and 428 m QRL) ~200 m 2 /m Multi Layer Insulation 128 permanently installed and remote controlled Turbomolecular 300l/s pumping systems ~400 positions to connect a mobile Turbomolecular pumping system – Stand alone cryostats (one insulation vacuum volume or subsector) 50 volumes/subsectors Average of 4 m 3 66 permanently installed and remote controlled Turbomolecular 60l/s pumping systems – High Vacuum system; ~10 -3 mbar at room temperature before cooldown, ~10 -7 mbar at cold 3 gauges (piezo, pirani and penning) on each volume Internal process line global leak tightness requirement <10 -8 mbarl/s He at warm per insulation vacuum volume Important quantities of water vapor during initial pumpdown Not very “clean” vacuum (variety of materials, dust, particles, swarfs…) 11th July 2011OLAV III; Session 23

4. LHC insulation vacuum system Typical vacuum instrumentation 11th July 2011OLAV III; Session 24

5. LHC insulation vacuum system 11th July 2011OLAV III; Session 25 A few numbers …

6. 300 l/s Turbo pump experience Up to 2008 (OLAV II) – 72 pumps (43%) with bearing failures – 6 pumps (8%) failed a second time after revision – 56% of the failures appears before 4000 hours of operation ~25% of nominal bearing lifetime – Long term storage error has been identified by the supplier as principal cause of early bearing failures 11th July 2011OLAV III; Session 26

7. 300 l/s Turbo pump experience 2009 – 23 pumps (26%)with bearing failures – 15 pumps failed a second time after revision – 52% of the failures appears before 8000 hours of operation ~50% of nominal bearing lifetime – Factory maintenance error has been identified as principal cause of repetitive bearing failures. 11th July 2011OLAV III; Session 27

8. 300 l/s Turbo pump experience 2010 – 8 pumps (17%) with bearing failures – 5 pumps failed a second time after revision – ~90% of the failures appears before the nominal bearing lifetime of 17 khours. – Most of the pumps achieved their nominal running hours. – Bearing failures before 17 khours are repaired under guaranty. 11th July 2011OLAV III; Session 28

9. 300 l/s Turbo pump experience 2011 – 2 pumps with bearing failures. (one within the nominal bearing lifetime and one above) – most of the pumps achieved their nominal running hours. – Accurate maintenance schedule using the regular LHC technical stops to exchange pumps which have made their 17 khours. – Stored exchange pumps are powered to rotate every month. 11th July 2011OLAV III; Session 29

10. 300 l/s Turbo pump experience 11th July 2011OLAV III; Session 210 Situation is under control; – Continuous operation of turbo’s No start-stop Automatic restart after power failures – Precise follow up of running hours – Every 17 khours (~2 years) bearing revision at manufacturer

11. 300 l/s Turbo pump experience 300 l/s Turbomolecular pumps for LHC insulation vacuum. – Local Turbo & controller/power supply in tunnel area with radiation levels <200 Gy – Turbo controller/power supply outside tunnel & radiation area 11th July 2011OLAV III; Session 211

12. Pressure Monitoring Each insulation vacuum volume has 3 gauges to monitor the vacuum [2000 - 10 -9 mbar]; – Piezo – Pirani – Penning Two types; – “high” radiation resistant (>10 5 Gy) – “improved” radiation resistant (<200 Gy) Intermittent operation for Penning when measuring in 10 -4 and 10 -5 mbar range Connected to the UPS (uninterruptable power system) Standard “catalogue” gauges for the “high” radiation resistance; – Passive series (no electronics or logics on gauge head) Piezo type APR017 (not produced any more) Pirani type TPR018 Penning type IKR070 On CERN request; modified gauges with “improved” radiation resistance; – Active series (minimum and limited radiation resistant electronics on gauge head and deported electronics to lower radiation area’s) Piezo type HUBA680 Full Range PKR251 with deported electronics 11th July 2011OLAV III; Session 212 Hardware

13. Pressure Monitoring PVSS supervision – data-logging – alarm generation Thresholds; – 500 mbar (piezo) – 1. 10 -2 and 1. 10 -1 mbar (pirani) Logics; – 1. 10 -2 pre-alarm to vacuum service only – 500 mbar or 1. 10 -1 gauge alarms to vacuum and cryogenics – 500 mbar and 1. 10 -1 in same volume; vacuum alarm to cryogenics (interlocks) 11th July 2011OLAV III; Session 213 Software

14. Pressure monitoring Pump- and cool down of an arc insulation vacuum subsector without leak (A19R6 in sector 6-7) 11th July 2011OLAV III; Session 214

15. Pressure monitoring Pump- and cool down of an arc insulation vacuum subsector with leak (A27L4 in sector 3-4) 11th July 2011OLAV III; Session 215

16. Leaks to insulation vacuum LHC insulation vacuum has actually 22 catalogued leaks; – 1 QRL (sector 4-5 volume B) – 21 Magnet; – 11 identified before cool-down <5. 10 -6 mbarl/s not localised and accepted for operation. – 11 identified during operation 2 leaks need the maximum technically possible additional permanent turbo-pumping to allow LHC operation. Limit of degraded insulation vacuum to continue LHC operation is 1. 10 -4 mbar. To ensure 200 days of LHC operation @ 1.9 K and 1. 10 -4 mbar; leaks > 5. 10 -6 mbarl/s need the permanently and additionally installed turbo pumping. 11th July 2011OLAV III; Session 216

17. Leak localisation LHC insulation vacuum volumes were designed with additional DN100 ISO- K “pumping ports at the volume extremities Additional mobile Turbo pumps (300 l/s) can be connected without breaking the vacuum 11th July 2011OLAV III; Session 217

18. Leak localisation An under vacuum leak test for longitudinal leak localisation uses two mobile turbo pumps and associated helium leak detectors. Assuming a linear conductance in the cryostat; For S>>C1 or C2; For LHC cryostats S ~ C; a correction has been applied for the effective pumping speed. 11th July 2011OLAV III; Session 218

19. Leak localisation All components, magnets, have been leak tested and validated leak- tight before lowering into the LHC tunnel. Only the interconnection work (welding) between magnets could generate new leaks. Leak localisation method, as mentioned in previous slide, indicates the interconnection concerned. Variations of gaseous helium pressure in different cryogenic circuits indicate the lines concerned. Detailed search; – Bubble spray (>10 -3 mbarl/s leaks) – Clam shell (local vacuum envelope for under vacuum test) Many leaks were localised with the combined longitudinal test followed by the clam shell test. 11th July 2011OLAV III; Session 219

20. LHC He & vacuum leaks 11th July 2011OLAV III; Session 220

21. LHC leaks 11th July 2011OLAV III; Session 221

22. LHC leaks 11th July 2011OLAV III; Session 222

23. LHC leaks 11th July 2011OLAV III; Session 223

24. 5 years of LHC Insulation vacuum experience; discussion points Turbo pumps; – Initial bearing failures storage and degradation of “greased for life” bearings? new product was still in ß-test phase? – ~20 khours bearing lifetime is this a standard for “greased for life” type of turbo pumps? – Permanent operation; is this common practice on insulation vacuum? – Hybrid design; combination with single stage rotary vane pumps a better technical and economical solution? Gauges; – Radiation resistance of nowadays intelligent, “active” compact vacuum gauges? – Gauges for high pressure readings P atm and radiation resistant? Leaks; – Some helium leaks already present at room temperature are stable (but larger) at cold. – Some new helium leaks appeared after thermal cycles; the big ones! 11th July 2011OLAV III; Session 224