The Greatest Lepton Collider aka LEP and LEP

The Greatest Lepton Collider aka LEP and LEP 2 The good, the bad, the ugly, the unforeseen: not to forget the humour Steve Myers

The very early days I left the ISR in 1979 to work under the leadership of Wolfgang Schnell in the LEP machine design team. The early design was led by Eberhard Keil, Wolfgang Schnell and Kees Zilverschoon. One of the important decisions was the circumference of the tunnel. The final decision, taken by Herwig Schopper was on the 26. 7 km variant which required 3 km of tunnelling inside the Jura mountains. In his book he wrote that “In view of the long-term future of CERN…a proton collider in the LEP tunnel…. it would be decisive to have as large a tunnel as possible. ” The final design for LEP was approved in December 1981 with Emilio Picasso as project leader, and construction of the tunnel started in 1983. 28 th November 2019, CERN S. Myers LEP 30 Colloquium 2

The Three Variants for the LEP/LHC Tunnel Chosen Variant (in red) gave Maximum Circumference possible between Geneva Airport and the Jura Mountains 28 th November 2019, CERN 3

Even with the reduced circumference, there was still a 3 km part of the tunnel in the foothills of the Jura, which had to be blasted. After blasting 2 km into the Jura, water burst into the tunnel, forming an underground river that took six months to eliminate. 4

The LEP/LHC Tunnel trace 27 km circumference underground diameter 4 m) S. Myers QUB tunnel March 11, (cross-section 2009 5

LEP Lay-Out 6

The injectors LIL – High current linac 200 Me. V/c – Low current linac 600 Me. V/c EPA PS SPS 600 Me. V/c 3. 5 Ge. V/c 20 Ge. V/c ( 22 Ge. V/c since 1996 ) Result: • 8 bunches of 1010 e+ and e- to LEP every 14. 4 s • availability almost 90% • not bad !!

Competition from a much smaller collider: SLC

Stanford Linear Collider (SLC) 28 th November 2019, CERN 11

Octant Test in 1988 By June 1987 part of the tunnel was complete and ready for installation and it was decided to install and test with a positron beam, a single octant. By July 1988, octant 8 was completely installed. On 12 July 1988, four bunches of positrons made the first successful journey between Point 1 and Point 2, – a distance of 2. 5 km through the first of eight sectors of the 27 -km LEP ring. Measurements made during the tests showed significant betatron coupling between the transverse planes. This was due to a nickel layer inside the vacuum chamber which was used to bond the lead to the aluminium. Discovering this coupling one year early was very valuable and justified the project leader’s insistence on the octant test. 28 th November 2019, CERN S. Myers LEP 30 Colloquium 12

First Circulating Beam: July 1989 • The following months saw a huge effort to install equipment in the remaining 24 km of the tunnel – magnets, vacuum chambers and RF cavities, as well as beam instrumentation, injection equipment, electrostatic separators, electrical cabling, water cooling, ventilation and all the rest. • Then, conditioning the cavities, baking out and leak testing the vacuum chambers, and individual testing of all components. • First beam was scheduled for 15 th July 1989. • At a quarter to midnight on 14 July 1989, (the 200 th anniversary of the storming of the Bastille), the beam made its first turn on the first attempt. Soon afterwards we managed to achieve a circulating beam, and we were ready to fine tune the multitude of parameters needed to prepare the beams for physics. 13

First Zo Events • One month after first beam, on August 14, we brought the beams into first collisions. • The next ten minutes seemed like an eternity since none of the experiments reported any events. • I was in the control room with Emilio (and we were beginning to wonder if the beams were actually colliding) when Aldo Michelini called from OPAL: “We have the first Z 0!” • The Zo bell 28 th November 2019, CERN S. Myers LEP 30 Colloquium 14

Emilio and Ian Wilson S. Myers, Twelve years of beam in LEP, . . , LEP Fest 2000, CERN, (LEPFest 2000. ppt), October 2000. 17

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

Short History with Beam • • 1988: July 12: Octant test 1989: • • • 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 28 th November 2019, CERN Exciting period, But usually not very productive Installation of sc cavities LEP 2 S. Myers LEP 30 Colloquium 19

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 20

Limitations and Solutions (the bad and the good) 28 th November 2019, CERN S. Myers LEP 30 Colloquium 21

Luminosity Performance Maximise: • Nb number of particles per bunch (limitation TMCI) • kb number of bunches; pretzel, bunch trains • y beam-beam tune shift Minimize: • y focus at the IP 28 th November 2019, CERN S. Myers LEP 30 Colloquium 22

Single Bunch Intensity Limitations: TMCI 28 th November 2019, CERN S. Myers LEP 30 Colloquium 23

More Bunches: Pretzel Scheme 28 th November 2019, CERN S. Myers LEP 30 Colloquium 24

More Bunches: Bunch Trains Scheme 28 th November 2019, CERN S. Myers LEP 30 Colloquium 25

Beam-Beam (the bad) 28 th November 2019, CERN S. Myers LEP 30 Colloquium 26

Limitations: Beam-Beam 1994, Pretzel Operation 28 th November 2019, CERN S. Myers LEP 30 Colloquium 27

Limitation: Beam-Beam 1995: 65 Ge. V 28 th November 2019, CERN S. Myers LEP 30 Colloquium 28

Beam-Beam Effect 1999: 98 Ge. V 28 th November 2019, CERN S. Myers LEP 30 Colloquium 29

Modes of Operation Every Year was Different: Chamonix Workshops 28 th November 2019, CERN S. Myers LEP 30 Colloquium 32

Summary of Performance 28 th November 2019, CERN S. Myers LEP 30 Colloquium 33

Performance 1993 -2000 34

The Unforeseen 28 th November 2019, CERN S. Myers LEP 30 Colloquium 44

Energy Calibration: Polarization 28 th November 2019, CERN S. Myers LEP 30 Colloquium 45

Very Use. Unexpected of transverse“Problem”: polarization Precise determination of the LEP beam energy (10 -5 relative accuracy, ~ 1 Me. V) Precise measurement of the Z mass and width Small changes of energy accurately measured (energy change from 1 mm circumference change) 28 th November 2019, CERN S. Myers LEP 30 Colloquium 46

Circumference variations 1993: Energy drifts over several weeks were traced to cyclical circumferences variations of ~ 2 mm/year Causes • Underground water • Rain • Lake level 28 th November 2019, CERN S. Myers LEP 30 Colloquium 47

Noise on the Beam Energy 28 th November 2019, CERN S. Myers LEP 30 Colloquium 48

TGV: The Fast Train • Influence on the beam energy – the moon, sun and tides – the level of lake Geneva – the amount of rain • AND the fast train. . 28 th November 2019, CERN S. Myers LEP 30 Colloquium 49

This effect was “missed” for many years because • Energy calibrations were performed during night shifts • On the occasion of energy calibration during a day shift the TGV was on strike! TGV induces current in LEP vacuum chamber 28 th November 2019, CERN S. Myers LEP 30 Colloquium 50

1996: Deliberate Sabotage Single Turn Stopper 28 th November 2019, CERN positrons S. Myers LEP 30 Colloquium QL 10. L 1 51

Zoom sur Quadrupole beer bottle 28 th November 2019, CERN S. Myers LEP 30 Colloquium 52

10 metres to the right beer bottle Unsociable sabotage: both bottles were empty!! 28 th November 2019, CERN S. Myers LEP 30 Colloquium 53

My present: Heineken Beam Stopper email card UK advertising at the time: Heineken; the beer that gets to places no other beer can! 28 th November 2019, CERN S. Myers LEP 30 Colloquium 54

Unintentional Sabotage Oops!! Problems with sextupole families tripping after about 1020 minutes: Brainstorming meeting: send teams to look inside the connection cabinets (27 kms) for the sextupole busbars 28 th November 2019, CERN S. Myers LEP 30 Colloquium 55

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, (LEPFest 2000. ppt), October 2000. 56

Even “Romeo and Juliette” were BAD • Quote from our LEP memoirs (unpublished) by Helmut Burkhardt, Willi Kalbreier, Mike Lamont, Steve Myers, John Poole. – Facts – Electrical short circuit dumped the beams – At the location of the short circuit, two deers were found dead (electrocuted) in a lovers’ embrace – Conclusion from the fact-finding team – Juliette bit into the electric cable – Romeo got a painful shock …. . 28 th November 2019, CERN S. Myers LEP 30 Colloquium 57

Increasing the Beam Energy (the “RF guys”: the good, but expensive!) 28 th November 2019, CERN S. Myers LEP 30 Colloquium 58

RF: pumping up the voltage (1999) n “The …RF system is now almost nearly ¨ Run at an energy where we have some RF margin ¨ fully operational”. Increase the RF voltage gradually Strategy to maximise physics time: 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, (LEPFest 2000. ppt), October 2000. 60

Year 2000: Run LEP 2 in 2001 or STOP? (The UGLY) 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 • no consensus 28 th November 2019, CERN S. Myers LEP 30 Colloquium 67

The abridged story of 2000 • 14 th June: First candidate event 206. 7 Ge. V – Reconstructed Higgs mass 114. 3 Ge. V/c 2 • 20 th July: LEP Committee – ALEPH present excess at high masses • 31 st July & 21 st Aug: events 2 & 3 for ALEPH – Things are heating up! • 5 th September: LEP Committee – Excess only in ALEPH, only 4 jets • September 14 th: Research board: – ONE MONTH run extension GRANTED (LHC startup) 28 th November 2019, CERN S. Myers LEP 30 Colloquium 68

October 10 th: LEPC: Update of the results The signal excess grows up to 2. 6 s 16 th October: Missing energy candidate from L 3. . . November 2 nd: end of LEP operations November 3 rd, LEPC: The new data confirm the excess again. The significance grows up to 2. 9 s LEP running in 2001 is requested November 3 rd LEPC - closed session: No unanimous recommendation November 7 th: Research board No unanimous recommendation (vote split 8 - 8) November 8 th DG decision (LM): “LEP has closed for the last time: ” 28 th November 2019, CERN S. Myers LEP 30 Colloquium 69

NOT A POPULAR DECISION! BUT the right one! This allowed massive redeployment of skilled and experienced CERN staff from LEP 2 to the LHC design. With this new focus, the design of the LHC gathered real momentum 28 th November 2019, CERN S. Myers LEP 30 Colloquium 70

Following the decision to close LEP LCC (LMC) Mission 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, • Evaluate experience with other relevant machines, • Create a competent, experienced trained team, • Prepare a detailed scenario for initial commissioning, • Specify special software requirements for commissioning and operation. LHC Commissioning Committee (LCC 1, now LMC) 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, WENNINGER Jorg http: //lhc. web. cern. ch/lhc/lcc. htm 71

What is the Legacy of LEP? The physics data (luminosity, energy calibration). Operation in unique regime of ultra-strong damping: - 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. Legacy to LHC Running large accelerators (shutdown planning, cold checkouts…) Training ground for future LHC leaders. Operation at high efficiency (controls software, control room management etc) Real-time feedback on beam parameters (orbit, tune, instabilities. . ) Running large Superconducting and cryo systems ……. 28 th November 2019, CERN S. Myers LEP 30 Colloquium 72

LEP: Design and Reality Parameter Design Achieved (55 / 95 Ge. V) (46 / 98 Ge. V) Bunch current 0. 75 m. A 1. 00 m. A Total beam current 6. 0 m. A 8. 4 / 6. 2 m. A Vertical beam-beam parameter 0. 03 0. 045 / 0. 083 Emittance ratio 4. 0 % 0. 4 % Maximum luminosity 16 / 27 1030 cm-2 s-1 23 / 100 1030 cm-2 s-1 IP beta function bx 1. 75 m 1. 25 m IP beta function by 7. 0 cm 4. 0 cm Reality better than design (result of many years work)! x 10 x 1. 4 / 3. 7 73

The last beam dump in LEP (2000); A sad occasion Goodbye my friends I must move on In the photo: • Roger Bailey, • Ralph Assmann, • Paul Collier, • Mike Lamont, • Steve Myers • Andy Butterworth 28 th November 2019, CERN S. Myers LEP 30 Colloquium 74

Some Logbook insertions • THE EIC IS NOT ON SHIFT TO BE INTIMIDATED BY PHYSICISTS ! • Q: Do you trust the BOM data ? A: I’m a physicist, not a priest • You can gain 20%, but you need some skill, which may be difficult for the OP group ! • I don’t know who/what controls the RF voltages. One thing’s for sure, it’s not me ! • If I were a positron, and I was asked to be launched into LEP on this trajectory, I would also refuse to accumulate! • the road to hell is paved with LEP extensions (2000) 28 th November 2019, CERN S. Myers LEP 30 Colloquium 75

Conclusions • LEP was a huge challenge, a lot of effort but enormously rewarding • The Physics output was exceptional • LEP training of accelerator and detector people allowed the rapid commissioning and exploitation of the LHC which allowed the rapid discovery of the Higgs’ boson. • LEP was a fantastic experience which will never be forgetten 28 th November 2019, CERN 76 S. Myers LEP 30 Colloquium

Thank you for your attention

Not Mentioned (from “LEP memoires”, unpublished, and probably unpublishable) • • The Polish electrician and the world’s most expensive screw-driver Bolek’s congratulations Make shift LEP control room Lack of applications software at start-up Logbook quotations The interaction between the Operations group and the experiments Names of “Golden Orbits” Chamonix “shenanigans”. 28 th November 2019, CERN S. Myers LEP 30 Colloquium 78

Excerpts from Mike Lamont’s analysis of a LEP fill • “Being an accelerator physicist at LEP took heart as well as brains. The Sisyphean daily task of coaxing the seemingly temperamental machine to optimal performance even led us to develop an emotional attachment to it. • So, what can go wrong when you're operating 27 kilometres of particle accelerator? The list is long: magnets, power converters, a vacuum system, a control system, a cryogenics system, a cooling and ventilation system, beam instrumentation – and much more. Then there was the control system, fibres, networks, routers, gateways, software, databases, separators, kickers, beam dump, radio-frequency (RF) cavities, klystrons, high-voltage sys-tems, interlocks, synchronisation, timing, feedback… And, of course, the experiments, the experimenters, and every-body’s ability to get along in a high-pressure environment. 28 th November 2019, CERN S. Myers LEP 30 Colloquium 79

Filling and Ramping • Filling and ramping were demanding periods during the operational sequence and a lot of concentration was required. The experiments did well not to ring and make too many demands at this stage. “Tell them to **** off” can, and did, cause offence. ” 28 th November 2019, CERN S. Myers LEP 30 Colloquium 80

Controlled Access(1) • I mean ****. I mean for Christ’s sake. This is the largest particle accelerator in the frigging world. Why can’t we get people in and out of the machine ……shut those bloody doors behind you. • …the first problem was getting them in. There was one access console, about 40 access doors all equipped with TV and intercom. Access was declared and war started. All over the ring, people starting buzzing the control room: I’m coming, please put in your card, take a key, the door has been released, no – put your key in the door and turn it, Ok I’ll re-release the door, try the key now, Hey! Only one person can go in on that card, no, you have to put your card in and take a key as well, no, I can’t let you in without a card, well you’re have to go back to your office and get it, I’m sorry. 28 th November 2019, CERN S. Myers LEP 30 Colloquium 81

Controlled Access(2) • Next problem: getting the buggers out. Two hours access scheduled, and after three, there’s some guy buried in the bowels of IP 1, uncontactable, diligently fixing whatever, with us apoplectic in the control room: “Right, that’s the last time he gets told that there’s an access coming up. ” • Recover from access was a random walk around interlock space as we tried to get the machine ready and safe for beam again. And, of course, there were the inevitable trips to the depths in point 5 to reset a door. Personally I used find something to do elsewhere and scoot during access if at all possible. 28 th November 2019, CERN S. Myers LEP 30 Colloquium 82

Golden Orbit Names • • The gold-plated plastic raincoat Dolce far niente. Not terrific but good for Delphi The magic mushroom Raperonzolo’s second baby (0. 068 bbts with 4. 9 m. A) Raperonzolo’s grand-daughter Baby Raperonzolo’s granddaughter for 45 Ge. V Raperonzolo’s black beast Ronny’s bete noir 28 th November 2019, CERN S. Myers LEP 30 Colloquium 83

1998 – a pretty bad year: • • • Burnt cables early on Timeout for emergency repairs Maximum beam-beam tune-shift 0. 055 Integrated luminosity for the year 105 pb-1 Karl-Heinz impeached GIORGIO CAVALLARI – HERO! 28 th November 2019, CERN S. Myers LEP 30 Colloquium 84

OP-RF encounters • “The …RF system is now almost nearly fully operational”. • This was the operations group official statement at Chamonix after the RF guys had pushed the system well above its design values and achieved a fantastic availability. The operations people are a demanding lot when it comes to equipment groups. 28 th November 2019, CERN S. Myers LEP 30 Colloquium 85