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the good, the bad, the ugly, and the unforeseen. From LEP to the LHC:. Abstract: I will try to point out the strong overlap and interconnection between the 2 colliders not only through the common tunnel but also through the people, the technologies, and accelerator science. Steve Myers.

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from lep to the lhc

the good, the bad, the ugly, and the unforeseen

From LEP to the LHC:

Abstract:

I will try to point out the strong overlap and interconnection between the 2 colliders not only through the common tunnel but also through the people, the technologies, and accelerator science

Steve Myers

some milestones
Some Milestones
  • ISR (proton-proton) (70s and early 80s)
  • LEP design started in the late 70s (Schnell Keil, Zilverschoon)
  • 1983 while designing LEP: proposal for LHC in same tunnel (LEP Note 440; Myers and Schnell)
  • 1989 First Collisions
  • 1989-2000 Operation
  • 2001-2003 Dismanteling

S. Myers From LEP to the LHC

slide3

From LEP to LHC Timelines

S. Myers From LEP to the LHC

slide4

From LEP to LHC Timelines

S. Myers From LEP to the LHC

slide5

(April 1983)

S. Myers From LEP to the LHC

some extracts from lep note 440
Some extracts from LEP Note 440
  • ..assume throughout that the maximum energy per beam is 8 TeV (9 T bending field) and injection is at 0.4 TeV.
  • We assume that a twin-ring pp collider would also employ bunched beams, a likely choice if only to limit the stored energy in the beams.
  • proposal by R. Palmer, pairs of magnets might be combined into "two-in-one" units, each having a common core and cryo- stat.
  • the use of protons in both beams permits higher luminosities, a large number of bunches, eliminating the problem of unresolvable multiple events within one bunch-bunch crossing.
  • the copper accelerating cavities will have already been replaced by superconducting ones before a p-LEP starts operation.
  • At the highest proton currents, the synchrotron radiation power becomes a problem for cold-bore magnets .
  • AcknowledgementThis work originated from a stimulating discussion with G. Briantiwho also gave us a first report of the most recent developments in the United States.
following lep note 440
Following LEP Note 440
  • LEP Note 450 (June 1983)
    • “Beam Separations in p-bar LEP” (Myers and Schnell)
  • LEP Note 460 (August 1983)
    • “Transverse Emittance and Beam Separation in a Large ppbar Collider” (Myers and Schnell)
  • LEP Note 470 (October 1983)
    • “Acceleration in the LEP Hadron Collider”. (Henke, Myers and Schnell)

S. Myers From LEP to the LHC

slide8

Very difficult period for LHC construction due to the parallel running on LEP2, SPS, PS, etcetc

Restructuring

difficult period for LHC approval. Approval of the (SSC) in 1987 severely jeopardized hopes for the approval of the less powerful LHC collider. Following a series of cost reviews which pushed the SSC cost from 4.4 billion to more than 11 billion dollars, the US congress cancelled the project in 1993.

S. Myers From LEP to the LHC

slide9

The LEP/LHC Tunnel trace

27km circumference underground tunnel (cross-section diameter 4m)

(was built for LEP collider in 1985)

S. Myers QUB March 11, 2009

9

slide10

LEP Lay-Out

S. Myers From LEP to the LHC

why was lep so big why sc rf
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

S. Myers From LEP to the LHC

competition from slc 1989 start up
Competition from SLC: 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 prodigious 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 From LEP to the LHC

short history with beam
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

S. Myers From LEP to the LHC

summary of performance
Summary of Performance

S. Myers From LEP to the LHC

modes of operation
Modes of Operation

Every Year was Different: Chamonix Workshops

S. Myers From LEP to the LHC

1989 start up
1989 Start-Up

S. Myers From LEP to the LHC

1993 2000
1993--2000

S. Myers From LEP to the LHC

slide20

Single Bunch Intensity Limitations: TMCI

S. Myers From LEP to the LHC

slide21

More Bunches: Pretzel Scheme

S. Myers From LEP to the LHC

slide22

More Bunches:BunchTrains Scheme

S. Myers From LEP to the LHC

beam beam the bad
Beam-Beam(the bad)

S. Myers From LEP to the LHC

slide24

Limitations: Beam-Beam

1994, Pretzel Operation

S. Myers From LEP to the LHC

slide25

Limitation: Beam-Beam

1995: 65GeV

S. Myers From LEP to the LHC

slide26

Beam-Beam Effect

1999: 98GeV

S. Myers From LEP to the LHC

and lifetime
 and lifetime

Inserting LEP parameters (+ y =4cm)

At 100 GeV and x=.07, tb =4.5 hours

Luminosity (x) is maximised by tuning on lifetime

S. Myers From LEP to the LHC

beam beam footprint
Beam-Beam Footprint

QV (98--99)

Cross half integer resonance 94.5; no problem

Qh (96--97)

S. Myers From LEP to the LHC

technical limitations the ugly
Technical Limitations(the ugly)

S. Myers From LEP to the LHC

limits 1998 antennae cable heating

damaged area

of cables

Beam tube

super insulation blanket

Limits 1998: Antennae Cable Heating
  • 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

S. Myers From LEP to the LHC

heating of rf antennae cables

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

S. Myers From LEP to the LHC

bunch length control during ramp
Bunch Length Control during Ramp

S. Myers From LEP to the LHC

ponderomotive oscillations
Ponderomotive Oscillations
  • At high beam current and high field, cavities oscillate mechanically at 100Hz

solution:

  • keep cavities on resonance:   0
  •  changes as a function of beam current  need different setpoints
  • new tuning/damping scheme

culprit: ponderomotive oscillations

growth rate  E2.( detuning angle)

S. Myers From LEP to the LHC

super bad a fortnight in hell mike
Super Bad: A Fortnight in Hell! (Mike)
  • 5 June RF unit dephased, lifetime 4 hours in physics
  • 5 June power supplyunstable
  • 5 & 7 Junetwo vacuum leaks in SPS plus fault on main power supply
  • 8 - 10 June transformer, vacuum valves, power supplies, access system, main power supply in SPS, problemswith the ‘ramp’ in LEP
  • 12 June vacuum leaknear a wire scanner, TWICE
  • 13 June vacuum valves blocked in position
  • 13 June RF frequencysynthesiserbroken
  • 13 Juin vacuum leak on a separator (local heating by SR)

S. Myers From LEP to the LHC

the unforeseen
The Unforeseen

S. Myers From LEP to the LHC

slide36

Energy Calibration: Polarization

S. Myers From LEP to the LHC

use of transverse polarization

Very Unexpected “Problem”:

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)

S. Myers From LEP to the LHC

slide38

Circumference variations

S. Myers From LEP to the LHC

slide39

Noise on the Beam Energy

S. Myers From LEP to the LHC

tgv the fast train
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.........

S. Myers From LEP to the LHC

tgv induces current in lep vacuum chamber
TGV induces current in LEP vacuum chamber

S. Myers From LEP to the LHC

1996 some things are sent to try us beam will not circulate
1996: Some things are sent to try us! (beam will not circulate)

Single Turn Stopper

QL10.L1

positrons

S. Myers From LEP to the LHC

zoom sur quadrupole
Zoom sur Quadrupole

beer bottle

S. Myers From LEP to the LHC

10 metres to the right
10 metres to the right

beer bottle

Unsociable sabotage: both bottles were empty!!

S. Myers From LEP to the LHC

my present heineken beam stopper email card
My present: Heineken Beam Stopperemail card

UK advertising at the time:

Heineken; the beer that gets to places no other beer can!

S. Myers From LEP to the LHC

slide47

Synchrotron Radiation: To keep ourselves sane!

We would write prose about our technical problems

During the cruel year of 1997 the evil Lord of Synchrotron Radiation came to wage war against the peaceful tribes of the LEP2 region in the province of PCR (Prevessin Control Room).

The Cruel Lord, with the help of his personal guard, the evil Wigglers, burned vacuum transitions, scorched separators and melted the lead homes of the tribe of the Pious Polarizers.

Antoni Gaudi would have been proud of the newly melted lead shielding installed to protect the polarimeter against synchrotron radiation

S. Myers From LEP to the LHC

slide48

Other Problems with cables

Where is the dirty rat who ate my cables?

S. Myers From LEP to the LHC

even romeo and juliette was bad
Even “Romeo and Juliette” was BAD
  • Quote from our LEP memoirs (unpublished)by Helmut Burkhardt, 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 …..

S. Myers From LEP to the LHC

increasing the beam energy the rf guys the good but expensive
Increasing the Beam Energy (the RF guys)(the good, but expensive!)

S. Myers From LEP to the LHC

rf pumping up the voltage
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

S. Myers From LEP to the LHC

with plenty of volts it s ok
With plenty of volts, it’s OK...
  • 2 days at 101 GeV ...
    • available RF voltage 3510 MV
    • margin 210 MV (2 klystrons can trip)
with a few less it s less easy
...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

slide54

2000: Need More Beam Energy:

As well as increasing the RF volts, we pulled out every trick we knew in order to squeeze the last drop of energy increase for the machine. E.g. using the horizontal orbit correctors as bending magnets.

Reducing Jx :

S. Myers From LEP to the LHC

tunnel movements affecting operation
Tunnel Movements Affecting Operation

LHC civil engineering (bad at the time, good now)

S. Myers From LEP to the LHC

performance in 2000
Performance in 2000

S. Myers From LEP to the LHC

performance in 20001
Performance in 2000

S. Myers From LEP to the LHC

year 2000 run lep2 in 2001 or stop
Year 2000: Run LEP2 in 2001 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
    • no consensus

S. Myers From LEP to the LHC

the abridged story of 2000
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 Mh114-115 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)

S. Myers From LEP to the LHC

slide60

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 3rd, 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

S. Myers From LEP to the LHC

slide61

NOT A POPULAR DECISION!

BUT the right one!

This allowed massive redeployment of skilled and experienced CERN staff from LEP2 to the LHC design. With this new focus, the design of the LHC gathered real momentum with L. Evans leading the overall project and the 3 accelerator department heads leading the technical design of the components (P. Lebrun (magnets, cryogenics and vacuum), P. Ciriani (infrastructure and technical services), S. Myers (radio frequency, accelerator physics, beam diagnostics, controls, injection extraction and beam dump, machine protection, and power supplies). It is important to highlight the enormous contributions of the CERN technical groups and group leaders in the design, fabrication, and testing of these very complex systems.

The strength of CERN is imbedded in its technical groups.

S. Myers From LEP to the LHC

slide62

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 trainedteam,
  • Prepare a detailed scenario for initial commissioning,
  • Specify special software requirements for commissioning andoperation.
  • Plan MD experiments for the LHC and its injectors

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, WENNINGER Jorg

http://lhc.web.cern.ch/lhc/lcc/lcc.htm

slide63

What is the Legacy of LEP?

  • The physics data (luminosity, energy, 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
  • …….
lep design and reality

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)!

slide65

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

S. Myers From LEP to the LHC

conclusions
Conclusions
  • LEP was a big challenge, a lot of effort but enormously rewarding
  • Physics output was exceptional
  • LEP training of accelerator and detector people allowed the rapid commissioning and exploitation of the LHC which resulted in the discovery of the Higgs’ boson.
  • LEP 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 (once again) all those people who worked on LEP/LHC and the detectors for their motivation, devotion and hard work. It was a fantastic experience which none of us will ever forget

S. Myers From LEP to the LHC

thank you for your attention

Thank you for your attention

S. Myers From LEP to the LHC