The LEP Machine Steve Myers SL CERN S

LEP Lay-Out S. Myers, Twelve years of beam in LEP, . . , LEP

Topics n n n Why is LEP so big? & Why is SC RF

Why is LEP so Big? Why SC RF? Losses due to Synchrotron Radiation E

Principal Performance Limitations n Beam Energy RF Volts (Gradients) ¨ Optics to a much

History of LEP with Beam n n 1988: July 12: Octant test 1989: W

1989 Start-UP n SLC The Economist August 19, 1989 “The results from California are

1989 Start-Up S. Myers, Twelve years of beam in LEP, . . , LEP

S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000,

Summary of Performance S. Myers, Twelve years of beam in LEP, . . ,

Modes of Operation Every Year was Different S. Myers, Twelve years of beam in

Performance over the Years S. Myers, Twelve years of beam in LEP, . .

Performance in 2000 S. Myers, Twelve years of beam in LEP, . . ,

Some Unexpected problems n 97/98 shutdown W many RF antennae cables electrically damaged, some

Heating of RF antennae cables • antennes used for cavity control • heated by

Bunch Length Control during Ramp S. Myers, Twelve years of beam in LEP, .

Other Problems with cables Where is the dirty rat who ate my cables? S.

Very Unexpected Problems: Moon S. Myers, Twelve years of beam in LEP, . .

Very Unexpected Problems: Water S. Myers, Twelve years of beam in LEP, . .

Noise on the Beam Energy S. Myers, Twelve years of beam in LEP, .

Very Unexpected Problem n Influence on the beam energy the moon, sun and tides

TGV induces current in LEP vacuum chamber S. Myers, Twelve years of beam in

RF: pumping up the voltage n Strategy to maximise physics time: ¨ ¨ ¨

Distribution of cavity gradients (96 to 104 Ge. V) 96 Ge. V: Mean Nb/Cu

With plenty of volts, we’re cruising. . . n After 2 days at 101

. . . with a few less, it’s less easy n Still at 101

The RF group’s 1999 collection n Q: 102 Ge. V: How did we get

Oops!! LEP repeatedly trips after 10 to 30 minutes. The time between trips decreases

Some really unexpected events Could not get the beam to circulate more than 15

Zoom sur Quadrupole beer bottle S. Myers, Twelve years of beam in LEP, .

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

1996: Heineken Beam Stopper S. Myers, Twelve years of beam in LEP, . .

Conclusions n n n LEP was a challenge and a lot of effort and

Slides: 35

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

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

Topics n n n 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 W n or Bed-time stories for your children and grand-children Concluding Remarks S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (OUT-2000 -139. ppt), October 2000. 3

Why is LEP so Big? Why SC RF? Losses due to Synchrotron Radiation E 0 =. 511 Me. V 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 LEP 1 was optimised for around 80 Ge. V with Cu cavities For sc cavities the power needed is “only” proportional to the 4 th power of energy. NOTE to operate LEP at 103 Ge. V with copper cavities would have needed 1280 cavities and 160 MW 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 S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (OUT-2000 -139. ppt), October 2000. 4

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

History of LEP with Beam n n 1988: July 12: Octant test 1989: W W W n n n n July 14, First turn (15 minutes ahead of schedule!) August 13, First Collisions Aug 13 --Aug 18: Physics pilot run Aug 21 --Sept 11: Machine Studies Sept 20 -- Nov 5 Physics 1990 --1994: Z physics 1995: Z + 65 & 70 Ge. V 1996: 80. 5 --86 Ge. V 1997: 91 --92 Ge. V 1998: 94. 5 Ge. V 1999: 96 --102 Ge. V 2000: 102 --104. 4 Ge. V Exciting period, But usually not very productive But LEP closure is one year (maybe 2) behind schedule S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (OUT-2000 -139. ppt), October 2000. 6

1989 Start-UP n SLC 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 27 km-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”. S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (OUT-2000 -139. ppt), October 2000. 7

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

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

Summary of Performance S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (OUT-2000 -139. ppt), October 2000. 10

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

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

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

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

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

Some Unexpected problems n 97/98 shutdown W many RF antennae cables electrically damaged, some melted damaged area of cables Beam tube super insulation blanket n Limitation on the beam current in 1998 bunch length dependent ¨ energy ramp modified to maximise the bunch length ¨ S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (OUT-2000 -139. ppt), October 2000. 16

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

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

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

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

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

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

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

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

RF: pumping up the voltage n 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. . . 100 Ge. V 101/100 Ge. V But. . . keeping it there requires a huge effort! 98 Ge. V 96 Ge. V S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (OUT-2000 -139. ppt), October 2000. 25

Distribution of cavity gradients (96 to 104 Ge. V) 96 Ge. V: Mean Nb/Cu 6. 1 MV/m 100 Ge. V: Mean Nb/Cu 6. 9 MV/m 104 Ge. V: Mean Nb/Cu 7. 5 MV/m S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (OUT-2000 -139. ppt), October 2000. 26

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

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

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

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 S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (OUT-2000 -139. ppt), October 2000. 30

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 positrons S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (OUT-2000 -139. ppt), October 2000. QL 10. L 1 31

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

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

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

Conclusions n n n 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 S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (OUT-2000 -139. ppt), October 2000. 35