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S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. The LEP Machine Steve Myers SL, CERN.

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Presentation on theme: "S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. The LEP Machine Steve Myers SL, CERN."— Presentation transcript:

1 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. The LEP Machine Steve Myers SL, CERN

2 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 2 LEP Lay-Out

3 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 3 Topics Why is LEP so big? & Why is SC RF needed? Principal Performance Limitations History of LEP with Beam Some unexpected problems Some really unexpected events  or Bed-time stories for your children and grand-children Concluding Remarks

4 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 4 Why is LEP so Big? Why SC RF? Losses due to Synchrotron Radiation 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 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 LHC For protons since E 0 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 E0 =.511MeV for electrons and 938.256 for protons

5 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 5 Principal Performance Limitations Beam Energy  RF Volts (Gradients)  Optics to a much less extent Luminosity  Beam current   Beam beam limit   Beam size at the interaction point (  *, emittance,..) Precision of the Energy calibration

6 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 6 History of LEP 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  But LEP closure is one year (maybe 2) behind schedule

7 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 7 1989 Start-UP 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”. SLC

8 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 8 1989 Start-Up

9 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 9

10 10 Summary of Performance

11 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 11 Modes of Operation Every Year was Different

12 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 12 Performance over the Years

13 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 13 Performance in 2000

14 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 14 Performance in 2000

15 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 15 Performance in 2000

16 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 16 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 Beam tube damaged area of cables super insulation blanket

17 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 17 Heating of RF antennae cables Cold Cable extrapolated From Measurements with beam antennes used for cavity control heated by coupling to beam 8W limit imposed 30 antennae in the last three weeks of running in 1998

18 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 18 Bunch Length Control during Ramp

19 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 19 Other Problems with cables Where is the dirty rat who ate my cables?

20 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 20 Very Unexpected Problems: Moon

21 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 21 Very Unexpected Problems: Water

22 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 22 Noise on the Beam Energy

23 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 23 Very Unexpected Problem Influence on the beam energy  the moon, sun and tides  the level of lake Geneva  the amount of rain AND the fast train.........

24 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 24 TGV induces current in LEP vacuum chamber

25 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 25 RF: pumping up the voltage 96 GeV 98 GeV 100 GeV 101/100 GeV 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!

26 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 26 Distribution of cavity gradients (96 to 104 GeV) 96 GeV: Mean Nb/Cu 6.1 MV/m 100 GeV: Mean Nb/Cu 6.9 MV/m 104 GeV: Mean Nb/Cu 7.5 MV/m

27 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 27 With plenty of volts, we’re cruising... After 2 days at 101 GeV...  available RF voltage 3510 MV  margin 210 MV (2 klystrons can trip)

28 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 28...with a few less, it’s less easy Still at 101 GeV...  but available RF voltage down to 3440 MV  margin 140 MV (1 klystron can trip) This fill at 100 GeV

29 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 29 The RF group’s 1999 collection Q: 102GeV: How did we get there??  A “by lowering luminosity and breaking cavities”. Q: Can we go further??  A: “Yes, by further lowering the luminosity and breaking MORE cavities”.

30 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 30 Oops!! LEP repeatedly trips after 10 to 30 minutes. The time between trips decreases with time unless you do not try to switch on. Problem was on the sextupole chains

31 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 31 Some really unexpected events QL10.L1 Single Turn Stopper positrons 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.

32 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 32 Zoom sur Quadrupole beer bottle

33 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 33 10 metres to the right beer bottle Unsociable sabotage: both bottles were empty!!

34 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 34 1996: Heineken Beam Stopper

35 S. Myers, Twelve years of beam in LEP,...., LEP Fest 2000,CERN,(OUT-2000-139.ppt), October 2000. 35 Conclusions LEP was a challenge and a lot of effort and fun Physics output was exceptional (still waiting for Higgs/SUSY) I would like to take this final (hopefully not!) opportunity to sincerely thank all the people who have worked on the LEP and the detectors for their motivation, devotion and hard work. It has been a fantastic experience for all of us


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