1. Luigi Serio CRYOGENICS PERFORMANCE AND OPERATION L. Serio, on behalf of the LHC Cryogenics Operation and Cryogenics Performance Panel

2. Luigi Serio2 Contents Introduction on cooling down and commissioning time Tuning loops adjustment & CV910 puppets – acquired knowledge and expected improvement Measured recovery time after quenches vs. theoretical expectations. DFBs filling Availability study for cryogenic system - can system components or related services be improved to maximize overall availability Improvement of He quality with new compressor. Translation to other sectors Vacuum minor leaks' impact on 1.9 K stability - improved strategy for GLPT in 45/81 Time to repair a fault occurring just before the week-end: is it adequate for running LHC? Is recovery time after problems resource dependant? If so, can extra resource be made available when required eg weekends, nights? Interlocks: New PIC-Cryo channels Is it likely that if multiple sectors are commissioned, a cryo problem in one sector will not affect other sectors – thus allowing effort to be put elsewhere?

3. Luigi Serio Global tuning And DFBs commissioning Powering Cool-down (Big gain expected) (2-3 wks w.r.t 9 wks)

4. Luigi Serio4 LHC Cryogenics: duration of cool-down phases Design LHC 7-8 Final 9 d 21 d 3 d 14 d 1 d 14 d 1 d 21 d 80 K 20 K 4.5 K 1.9 K Total Design LHC 7-8 Final Design LHC 7-8 Final Design LHC 7-8 Final Design LHC 7-8 Final 14 d / 2 wks 70 d / 10 wks ELQA 14 d 4 d 3 d 7 d 28 d / 4 wks Excluding ELQA or extra-works : Sketches intended to illustrate achievements and ultimate expectations S. Claudet - Jul’07

5. Luigi Serio5 Data for LHC scheduling purposes First time a given cryoplant type is used: 4-5, 8-1, 3-4, 7-8:8 wks + ELQA Second time a given cryoplant type is used: 5-6, 6-7:6 wks + ELQA For 2008 onwards: 4-5, 3-4:4 wks + ELQA Warm-up: Complete sector: 4 wks the first time (Design: 2 wks) QRL + some cells: 2 wks Proposed durations with expected learning effects to be checked autumn 2007 S. Claudet - Jul’07

6. Luigi Serio6 Tuning loop adjustments June 18: Simultaneous, sawtooth ramping of D2 and Q4

7. Luigi Serio7 Tuning loop adjustments

8. Luigi Serio8 Valves: Flow caracteristics Installed R ~ 25 New R ~ 100 Large sensitivity gain

9. Luigi Serio9 Availability: From 7-8 to others DFBMs Cryo Maintain LSS: 85% (Since 1st May) DFBAs Cryo Maintain ARC: 66% (Since 1st June) Target LSS: 90% (incl. time lost for quench recovery) Target ARC: 80% (incl. time lost for quench recovery)

10. Luigi Serio

11. Quench recovery for one quadrupole  Quench 720 A => TTregulation + 20 mK  Quench 2000 A => TTregulation + 200 mK & 5 minutes for Cryostart (2 K)  Quench 6500 A => TTregulation + 1.3 K & ~ 40 minutes for Cryostart (< 2 K)  New : Quench 2 x 6500 A => TTregul + 4 K & 2h30 for Cryostart (< 2 K) => No effect on cold compressors NB : Cryostart recovery time not yet optimised (presence output limit high on JT valve to limit overshoot)

12. Luigi Serio12 Recovery Time after Limited Resistive Transitions More than 14 cells or full sector  recovery up to 48 hours In case of fast discharge (even w/o quench)  2 h recovery (heating due to eddy currents).

13. Luigi Serio13 Interlocks: New PIC-Cryo channels For operation reasons a cryo-start signal for 60 Amps will be implemented taking into account beam screen temperature (heat intercept) and eventually the thermal screen temperature Details to be discussed with system owner and PIC team To be implemented already for sector 4-5

14. Luigi Serio14 Helium quality for distribution Improvement of He quality with for other refrigerators (sectors)  Problem only for ex-LEP cryoplants from Air Liquide for which the sub-cooler was just made for isothermal refrigeration (LEP) and not for non-isothermal refrigeration (LHC)  Problem identified Autumn’06  Proposal received for modification, but no agreed yet  The change of refrigerator did not show big impact on commissioning. Major gain to be expected in pseudo liquefaction mode when re-filling after a stop

15. Luigi Serio15 Vacuum minor leaks No major problems for stability /cooling power with the levels accepted in sector 7-8 Can have (depending on the level) some impact on recovery time More problematic is the leak (no connection) of the Y tube in the bayonet heat exchanger –Can still function with adjacent cell but increase in recovery of cryo start conditions (cooldown)

16. Luigi Serio16 Time to repair a fault outside working hours Time to repair a fault occurring just before the week-end: is it adequate for running LHC? => We are not running the LHC we are commissioning it and cryogenics is part of the commissioning … Is recovery time after problems resource dependant? If so, can extra resource be made available when required eg weekends, nights?  Efforts put on control logic (long term) rather than on manpower (short term)  Furthermore resources need to be trained or be expert in the domain for most of the problems encountered  Efforts and intervention are anyway already performed during the weekends and nights even if you do not realize it Is it likely that if multiple sectors are commissioned, a cryo problem in one sector will not affect other sectors – thus allowing effort to be put elsewhere? => YES, machines and teams independent