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LEP Operation

LEP Operation. Steve Myers CERN. Chapters. Before Powerpoint After Powerpoint. 1989 - commissioning. 14th July: first beam 23rd July: circulating beam 4th August: 45 GeV 13th August: colliding beams. Many of these people are to blame for what followed.

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LEP Operation

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  1. LEP Operation Steve Myers CERN

  2. Chapters • Before Powerpoint • After Powerpoint

  3. 1989 - commissioning • 14th July: first beam • 23rd July: circulating beam • 4th August: 45 GeV • 13th August: colliding beams Many of these people are to blame for what followed

  4. We are hoping to do this for LHC during next week-end

  5. The Economist August 19, 1989 “The results from California are impressive, especially as they come from a new and unique type of machine. They may provide a sure answer to the generation problem before LEP does. This explains the haste with which the finishing touches have been applied to LEP. The 27km-long device, six years in the making was transformed from inert hardware to working machine in just four weeks--- a prodigous feat, unthinkable anywhere but at CERN.............. ........Even so, it was still not as quick as Dr. Carlo Rubbia, CERN’s domineering director-general might have liked”.

  6. After powerpoint

  7. Why was LEP so Big? Why SC RF? Losses due to Synchrotron Radiation E0 = .511MeV for electrons and 938.256 for protons Power Dissipated in the walls of the Cu cavities Power to Beam from the SC cavities..... So to minimise power you need  to be as large as possible i.e. large radius. The radius for LEP1 was optimised for around 80GeV with Cu cavities LHC For protons since E0 is a factor of 1836 higher, the RF power is not an issue and the bending radius can be made as low as is technically possible. i.e. High fields For sc cavities the power needed is “only” proportional to the 4th power of energy. NOTE to operate LEP at 103 GeV with copper cavities would have needed 1280 cavities and 160MW of RF power!! Impossible for many reasons

  8. Performance up to 2000

  9. Short History with Beam • 1988: July 12: Octant test • 1989: • July 14, First turn (15 minutes ahead of schedule!) • August 13, First Collisions • Aug13--Aug 18: Physics pilot run • Aug 21--Sept 11: Machine Studies • Sept 20-- Nov 5 Physics • 1990--1994: Z physics • 1995: Z + 65 & 70 GeV • 1996: 80.5--86 GeV • 1997: 91--92 GeV • 1998: 94.5 GeV • 1999: 96--102 GeV • 2000: 102--104.4 GeV  Exciting period, But usually not very productive

  10. Summary of Performance

  11. Modes of Operation Every Year was Different

  12. RF: pumping up the voltage • Strategy to maximise physics time: • Run at an energy where we have some RF margin • Increase the RF voltage gradually • When stable at sufficient voltage, increase the energy • Drink the champagne • Repeat as many times as possible... But... keeping it there requires a huge effort! 101/100 GeV 100 GeV 98 GeV 96 GeV

  13. Parameter Design (55 / 95 GeV) Achieved (46 / 98 GeV) Bunch current 0.75 mA 1.00 mA Total beam current 6.0 mA 8.4 / 6.2 mA Vertical beam-beam parameter 0.03 0.045 / 0.083 Emittance ratio 4.0 % 0.4 % Maximum luminosity 16 / 27 1030 cm-2s-1 23 / 100 1030 cm-2s-1 IP beta function bx 1.75 m 1.25 m IP beta function by 7.0 cm 4.0 cm LEP: Design and Reality x 10 x 1.4 / 3.7 Reality better than design (result of manyyears work)!

  14. The Unforeseen and Unexpected

  15. Beam tube Some Unexpected problems • 97/98 shutdown • many RF antennae cables electrically damaged, some melted • Limitation on the beam current in 1998 • bunch length dependent • energy ramp modified to maximise the bunch length damaged area of cables super insulation blanket

  16. Cold Cable extrapolated From Measurements with beam Heating of RF antennae cables • antennes used for cavity control • heated by coupling to beam • 8W limit imposed • 30 antennae in the last three weeks of running in 1998

  17. Bunch Length Control during Ramp

  18. Oops!! LEP repeatedly trips after 10 to 30 minutes. The time between trips decreases with time unless you do not try to switch on. Send army of teams to check on the sextupole chain connections

  19. Other Problems with cables Whereis the dirty rat whoatemycables? LHC has a bird and a baguette

  20. Romeo and Juliette LEP was brought down by an electrical distribution fault. At the scene of the fault, two deers were found electrocuted but still in a lover’s embrace (poetic!) • Juliette alone had bitten into the offending electrical cable. • Must have been very Painful for Romeo. LHC has a bird and a baguette

  21. Very Unexpected Problems: Water Lake Geneva

  22. Very Unexpected Problems: Moon Use of transverse polarization Precise determination of the LEP beam energy (10-5 relative accuracy, ~ 1 MeV) Precise measurement of the Z mass and width Small changes of energy accurately measured (energy change from 1mm circumference change) LEP energy affected by: Tides, water levels, …

  23. Noise on the Beam Energy First time we measured many weeks before the signal was noise free

  24. Very Unexpected Problem • AND now the fast train.........

  25. TGV induces current in LEP vacuum chamber First time we measured many weeks before the signal was noise free; Train workers were on strike that week!!!

  26. Some really unexpected events Could not get the beam to circulate more than 15 turns even with large bumps all around the ring. Use single turn orbit system and normalised the measurement. Single Turn Stopper QL10.L1 positrons

  27. Zoom in on Quadrupole Heineken beer bottle

  28. 10 metres to the right Second beer bottle Unsociable sabotage: both bottles were empty!!

  29. 1996: Heineken Beam Stopper UK advertising at the time: Heineken; the beer that gets to places no other beer can!

  30. Performance in 2000

  31. Peak luminosity LEP2 LEP1 Design LEP1: Very realistic design estimates (well-known regime) LEP2: Benefits from strong synchrotron radiation damping (too risky to put into design)

  32. Delivered luminosity per day LEP2 LEP1 Continual improvement even for same peak luminosity! Important input for future big projects…

  33. Performance in 2000

  34. Distribution of cavity gradients (96 to 104 GeV) 100 GeV: Mean Nb/Cu 6.9 MV/m 96 GeV: Mean Nb/Cu 6.1 MV/m 104 GeV: Mean Nb/Cu 7.5 MV/m

  35. Beam energy (year) Average accelerating field [MV/m] 96 GeV (1999) 6.1 100 GeV (1999) 6.9 104 GeV (2000) 7.5 Available RF voltage Design: 6 MV/m

  36. Year 2000 The Decision to continue or STOP • LEP vs LHC (old vs new) • running LEP would delay LHC by 0, 1, 1.5, 2 (?) years • the competition with Tevatron • manpower transfers needed from LEP to LHC • “materials“ budget considerations (+electrical power etc) • The first and only Civil war in CERN • brothers against brothers, colleagues against colleagues • no consensus • Very Difficult Times and difficult decisions

  37. The abridged story of 2000 • 14th June: First candidate event 206.7 GeV • Reconstructed Higgs mass 114.3 GeV/c2 • 20th July: LEP Committee • ALEPH present excess at high masses • Not seen by other experiments BUT combined excess for mass hypothesis of 115 GeV/c2 of 1.1. • 2 reserve weeks - end of September granted • 31st July & 21st Aug: events 2 & 3 for ALEPH • Things are heating up! • 5th September: LEP Committee • Excess only in ALEPH, only 4 jets • Combination however agrees with Mh 114-155 GeV/c2 • Request 2 months extension • To double amount of lumiat 206.5 GeV which had already been collected. • September 14th: Research board: • ONE MONTH GRANTED (LHC startup) LEP to the limit

  38. October 10th: LEPC: Update of the results • The signal excess grows up to2.6s • 16th October: Missing energy candidate from L3... • November 2nd: end of LEP operations • We only managed about 50% of request to double sample. (half the time half the integrated lumi) • November 3d LEPC: The new data confirm the excess again. The significance grows up to 2.9s LEP running in 2001 is requested • November 3rd LEPC - closed session: • No unanimous recommendation • November 7th: Research board • No unanimous recommendation (vote split 8 - 8) • November 8th: “LEP has closed for the last time: Additional 2001 running not granted LEP to the limit

  39. NOT A POPULAR DECISION! LEP to the limit

  40. Evolution 2.9s 2.6s 2.2s Results coherent with the presence of a Higgs boson with mass 115 GeV/ c2 1.1s LEP to the limit

  41. The last beam in LEP (2000); A sad occasion I had to prepare the dismantling with my LEP colleagues AArrggHH! Goodbye my friends I must move on • In the photo: • Roger Bailey, • Ralph Assmann, • Paul Collier, • Mike Lamont, • Steve Myers • Andy Butterworth

  42. So…LHC got the tunnel and Pikachu: Possible aperture limit LEP to the limit

  43. What is the Legacy of LEP? The physics data (luminosity, energy, energy calibration). The experience in running large accelerators.- Technical requirements to control a large-scale facility.- Operational procedures for high efficiency.- Orbit optimization in long machines.- Alignment, ground motion and emittance stability in deep tunnels.- Designing and running a large SC RF system.- Impedance and TMCI in long machines.- Optics designs from 60/60 to 102/90 and 102/45. Operation in unique regime of ultra-strong damping:- Vertical emittance with small solenoid effects (dispersion-dominated).- Beam-beam limit with strong damping.- First confirmation of theory of transverse spin polarization. LEP will be the reference for any future e+e- ring collider design.

  44. The Continuing Legacy of LEP in the LHC LCC Mandate February 14, 2001 • Use the experience and expertise gained in LEP to Prepare beam commissioning and operation of the LHC collider • " • Evaluate and maximise the performance of the injectors. • ) • Organise and evaluate experience with other relevant machines • * • Prepare a detailed scenario and create a competent and appropriately experienced and trainedteam for initial commissioning. • Examine and specify special software requirements pertaining to machine commissioning andoperation. • Plan and examine the results of MD experiments pertaining to the machine and its injectors • Proposals of design changes to equipment groups on topics pertaining to commissioning,operation or performance of the machine. LHC Commissioning Committee (LCC 1) BAILEY Roger, CLAUDET Serge, CORNELIS Karl,  EVANS Lyn, FAUGERAS Paul, FERNQVIST Gunnar, JEANNERET Jean-Bernard,  KOUTCHOUK Jean-Pierre,  LAMONT Mike,  LINNECAR Trevor,  MERTENS Volker,  MYERS Steve (Chair),    POOLE John, PROUDLOCK Paul, ROY Ghislain, RUGGIERO Francesco,   SABAN Roberto,  SASSOWSKY Manfred,  SCANDALE Walter,   SCHMICKLER Hermann, SCHMIDT Rudiger, TSESMELIS Emmanuel, WENINGER Jorg http://lhc.web.cern.ch/lhc/lcc/lcc.htm

  45. Conclusions • LEP was a big challenge, a lot of effort but enornously rewarding • Physics output was exceptional • LEP accelerator achievements are based on the work of many hundreds of CERN technicians, engineers, and physicists from 1978 to 2000. 554 papers were published in Proceedings of the Chamonix workshops alone (from 118 authors). • I would like to take this final opportunity to sincerely thank (again) all these people who worked on LEP and the detectors for their motivation, devotion and hard work. It has been a fantastic experience which none of us will ever forget

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