The LEP Machine

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

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

LEP Lay-Out


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


Why is LEP so Big? Why SC RF?

sh28

0

8b

sh

2RF

Cu lr11

EE

lrVP

sRF40

4b

0 sinV1EEU

tot

40

4b

0totscI

EEUIP

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 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

E0 = .511MeV for electrons and 938.256 for protons


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


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


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


1989 Start-Up



Summary of Performance

Year int L Eb kb 2 kb Ib Peak Lumi y

(pb-1) (GeV) (mA) (10^30 cm-2 s-1) 1989 1.7 45.6 4 2.6 4 0.0171990 8.6 45.6 4 3.6 7 0.0201991 18.9 45.6 4 3.7 10 0.0271992 28.6 45.6 4/8 5.0 12 0.0271993 40.0 45.6 8 5.5 19 0.0401994 64.5 45.6 8 5.5 23 0.0471995 46.1 45.6 to 70 8/12 8.4 34 0.0301996 24.7 80.5 to 86 4 4.2 36 0.0401997 73.4 90 to 92 4 5.2 47 0.0551998 199.7 94.5 4 6.1 100 0.0751999 253.0 98 to 101 4 6.2 100 0.083


Modes of Operation

Year Optics Comments Bunch scheme 1989 60/60 LEP commissioned 4 on 4 1990 60/60 4 on 4 1991 60/60 90/90 optics tested 4 on 4 1992 90/90 Pretzel commissioned 4 on 4 / Pretzel 1993 90/60 Pretzel 1994 90/60 Pretzel 1995 90/60 tests at 65-68 GeV Bunch trains 1996 90/60 108/90 tested 4 on 4 1997 90/60 108/60 and 102/90 tested 4 on 4 1998 102/90 4 on 4 1999 102/90 4 on 4

Every Year was Different


Performance over the Years


Performance in 2000


Performance in 2000


Performance in 2000


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 areaof cables

super insulation blanket


Heating of RF antennae cables

Room Temp.Test Cable

200.0

250.0

300.0

350.0

400.0

450.0

500.0

550.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Power [W]

Tem

p [K

]

200

523

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


Bunch Length Control during Ramp

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

13:48:00 13:50:53 13:53:46 13:56:38 13:59:31 14:02:24 14:05:17

Time

Beam

Cur

rent

/ Cab

le P

ower

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Wig

gler

Fie

ld /1

0*Q

s / B

unch

Len

gth(

cm)

DC CurrentCablePowQsDwiggEwiggP3WiggP7WiggBunch Length

Fill 5300


Other Problems with cables

Where is the dirty rat who ate my cables?


Very Unexpected Problems: Moon


Very Unexpected Problems: Water


Noise on the Beam Energy


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.........


TGV induces current in LEP vacuum chamber


2900

3000

3100

3200

3300

3400

3500

3600

20/5

/99

27/5

/99

3/6/

99

10/6

/99

17/6

/99

24/6

/99

1/7/

99

8/7/

99

15/7

/99

22/7

/99

29/7

/99

5/8/

99

12/8

/99

19/8

/99

26/8

/99

2/9/

99

9/9/

99

16/9

/99

23/9

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30/9

/99

7/10

/99

14/1

0/99

21/1

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28/1

0/99

4/11

/99

Date

MV Copper

SC

RF: pumping up the voltage

96 GeV

98 GeV

100 GeV101/100 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!


0

5

10

15

20

25

30

Accelerating field [MV/m]

Num

ber o

f cav

ities

96 GeV100 GeV104 GeV

Distribution of cavity gradients (96 to 104 GeV)

96 GeV:Mean Nb/Cu6.1 MV/m

100 GeV:Mean Nb/Cu6.9 MV/m 104 GeV:

Mean Nb/Cu7.5 MV/m


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)

0

10

20

30

40

50

60

70

80

90

100

07-Oct 10:50 07-Oct 15:38 07-Oct 20:26 08-Oct 01:14 08-Oct 06:02 08-Oct 10:50

Lum

inos

ity/ 1

0+30

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

Bea

m C

urre

nt /m

A

AlephDelphiL3OpalIDC


0

10

20

30

40

50

60

70

80

90

100

04-Nov 00:00 04-Nov 02:24 04-Nov 04:48 04-Nov 07:12 04-Nov 09:36 04-Nov 12:00 04-Nov 14:24 04-Nov 16:48 04-Nov 19:12

Lum

inos

ity/ 1

0+3

0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

Bea

m C

urre

nt /m

A

AlephDelphiL3OpalIDC

...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


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”.


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


Some really unexpected events

QL10.L1Single 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.


Zoom sur Quadrupole

beer bottle


10 metres to the right

beer bottle

Unsociable sabotage: both bottles were empty!!


1996: Heineken Beam Stopper


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

Documents

The LEP Machine