lep operation and performance - cornell university...65.0 0.050 249 91.5 0.055 89 94.5 0.075 81 98.0...

10/25/2001 Cornell October 2001 1

LEP Operation and Performance

Outline:

1) Brief History2) Injection & TMCI3) Beam-beam tune shift & Luminosity performance4) Optimisation5) Equipment6) Operations, controls and instrumentation6) Polarization6) Other issues7) Conclusion

Mike Lamont, CERN

Will try and concentrate on physics & lessons that

might be relevant to future machines.


1989 First operation

1989-1995 The Z-years(precision studies)

1996-1999 The W-years(precision studies)

2000 The Higgs-year(almost a discovery?)

Nov 2000 Start of dismantling

LEP - The Largest Particle Accelerator to Date…


1989-2000

0102030405060708090

100110

1989 1991 1993 1995 1997 19990

50

100

150

200

250

300

Energy Peak luminosity Integrated luminosity


History

4 on 4102/901999

4 on 460/6019904 on 490/90 tested60/601991

4 on 4/ PretzelPretzel commissioned90/901992Pretzel90/601993Pretzel90/601994

Bunch trainsTests at 65-68 GeV90/6019954 on 4108/90 tested90/6019964 on 4108/90 & 102/90 tests 90/601997

4 on 4Higgs discovery mode102/902000

4 on 4102/901998

4 on 4Commissioning60/601989

BUNCH SCHEMECOMMENTOPTICSYEAR


1989 - commissioning

• 14th July: first beam• 23rd July: circulating beam• 4th August: 45 GeV• 13th August: colliding beams

These people are to blame for what followed


1990 – operational teething troubles• Luminosity: 2 - 3 1030 cm-2 s-1

• Beam current around 3 mA • Pretzel test• Lots of waist scans• BIG beam sizes…

8.6 pb-1

Conclusion from Chamonix 91

• a 70/76 team has been set up

• a dispersion team has been set up

• a dynamic aperture team has been set up

• a closed obit team has been set up

• an intensity limitation team has been set up

• a longitudinal oscillation team has been set up

• a crash pretzel team has been set up

• a beam-beam team already exists!


1999 - cruising

BORING!

253 pb-1


Performance

• Two distinct regimes:– 45.625 GeV characterised by working well into the soft beam-beam limit

and approaching the hard limit.– 80.5 GeV and above

• Staged installation of RF cavities• Maximum collision energy (c.m.) raised to 209 GeV• Accelerator physics regime of ultra-rapid damping• Not beam-beam limited

• 2000: Operational strategy to maximize discovery reach with operation in the regime of ultra-rapid damping


Injection

• A lot of effort in to pushing the bunch current in anticipation of high energy,

• Efficiency always variable, synchrotron injection used• In the end limited way below maximum by RF system (power

levels and stability)• Fundamental limit at LEP TMCI which was eventually reached

despite more practical problems – coherent tune shift & resonances (in particular synchro-betatron)– Increase injection energy– Removal of copper RF cavities– Increase of synchrotron tune– wigglers

• Some evidence that long-range beam-beam reduced TMCI limit


(ignore hardware, RF considerations)Transverse mode coupling instability (TMCI):

Influence from beam-beam: Lower TMCI threshold by ~ 12 %

Synchro-betatron resonances (SBR):

Longitudinal single-bunch instability: Not understood. Avoided with bunchlengthening.

∑ ⊥

=)(

2

s

srevth ke

QfEIσβ

π

+ 1.5 %

Raise Qs (also helps RF)Experimentallyfound 1998 to bearound ~ 1 mA

Qv = n · Qs with n = 1, 2, 3(coherent and incoherent)

AvoidSBR

Injection limits in 1998


(MD-results by P. Collier, G. Roy, R. Assmann and K. Cornelis, M. Lamont, M. Meddahi)

1998 standard workingpoint (SWP):

Qh = 0.28Qv = 0.23Qs = 0.132

780 µA per bunch reached with two beams…

Extended up to ~ 940 µA in single electron bunch MD

(chromaticities ~ 1-2)

LEP working Points:


Qh = 0.29Qv = 0.30Qs = 0.142

High Qv workingpoint:

1030 µA per bunch in 4 bunches (limited by TMCI).

Qs > 0.144 inconclusive. Qs = 0.16, 0.166, 0.174 with 850 µA per bunch.(low injection efficiency 20%, injection would require re-optimisation).

(single beam, separators off)

(lowered chromaticities by 0.5)

New working point (Cornelis, Lamont, Meddahi):


20001999

1998

Overview of Luminosity and Energy Performance


With the strong transverse damping (60 turns at 104 GeV)…

… second beam-beam limit (tails, resonances) is overcome… beam-beam limit is pushed upwards… we then profit from smaller IP spot size and higher currents… 1/3 resonance can be jumped… beams can be ramped in collision with collimator closed

… but also…

… no radiative spin polarization above 61 GeV (energy calibration)

Unique experience with ultra-strong damping at LEP

Why was high energy so good for LEP?


Vert. beam-beam parameter: *

2e e y b

rev x y by

r m i Le f E i

βπ σ σ

ξ⋅ ⋅ ⋅

= ∝⋅ ⋅ ⋅ ⋅

31 /y Eξ ∝ naively

Beam-beam limited

Energy ξy (max) Damping[GeV] per IP [turns]

45.6 0.045 72165.0 0.050 24991.5 0.055 8994.5 0.075 8198.0 0.083 73101 0.073 66102-104 0.055 63

Beam-beam limit not reached

Observed in LEP (1994-2000):

Strong damping

Beam-beam limitpushed upwards

Peak luminosity: 1032 cm-2 s-1

σxσy from 45.6 GeV to 98 GeV:

Reduced by factor ~ 1.6 (factor ~2 in σy)


Beam behavior at high energy:

Larger emittances / energy spread (ε ~ E2, σE/E ~ E)• Less luminosity• Higher backgrounds

Solenoid coupling is weaker (θ ~ 1/E with B=const)• Residual coupling contributes less to vertical emittance

Strong transverse damping (τ ~ 1/E3, 60 turns at 104 GeV)• Second beam-beam limit (tails, resonances) is overcome• Higher beam-beam tune shifts with higher beam-beam limit• 1/3 resonance can be jumped• Beams can be ramped in collision

Luminosity Performance at High Energy


Horizontal beam size: / rmsxx x x x xJ D Eβ εσ β∝ ⋅= ⋅

Compensate increase with energy (smaller luminosity, larger background):

1) High Qx optics with smaller Dxrms (D. Brandt et al, PAC99)

2) Smaller βx* (2.0 m - 1.5 m - 1.25 m)

3) Increase damping partition number Jx via RF frequency

0102030405060708090

100110

00:40 01:00 01:20 01:40 02:00 02:20 02:40 03:00

∆ R

F fr

eque

ncy

[Hz]

Time

Safety settingJx = 1.04(larger σx)

Jx = 1.6 (smaller σx)

Jx = 1.4

101 GeVAutomatic controlJx = function (URF)

For highest energy reach: Reduce Jx.


Scaling empirically fitted by Keil, Talman, Peggs, …

Several points in a given machine, similar configuration for LEP.

Independent cross-check of previous results, however:

• Beam-beam limit reached at 45.6 GeV• Beam-beam limit not reached

Can we infer the beam-beam limit at high energy?

Look at functional dependence of beam-beamparameter on bunch current…

What Is the Energy Dependence of the Beam-beam Limit?


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 200 400 600 800 1000

Ver

tical

bea

m-b

eam

par

amet

erBunch current [µA]

98 GeVSimple model used to fit unperturbedemittance and beam-beam limit:

Two fit parameters A and B:

( )21

y bbA B

ii

ξ = ⋅+ ⋅

20

*0

*

2y

xx

e y

eA fr

β επ γ εβ

= ⋅ ⋅ ⋅

( )1

y b

Biξ

=→ ∞

No BB blow-up

ξy (asymp) = 0.115εy (no BB) = 0.1 nm 0

50

100

150

200

250

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Lum

inos

ity [1

030 c

m-2

s-1

]Vertical emittance [nm]

With BB limit

No BB limit

Limited gainin luminositywith εy:

Vertical Beam-beam Blow-up


Dependence of vertical beam-beam tune param.on bunch current I (in the regime of strongsynchrotron radiation, K. Cornelis): ( )2

1y i

A B iξ = ⋅

+ ⋅

Two fit parameters A and B:

Knowing all other parameters, A is just givenby the unperturbed vertical emittance. Withouta beam-beam limit:

20

*0

*

2y

xx

e y

eA fr

β επ γ εβ

= ⋅ ⋅ ⋅

1y i

Aξ = ⋅

1( )y

Biξ

=→ ∞

B gives the asymptotic beam-beam limit of the vertical beam-beam parameter:

• Beta beat due to beam-beam not included• Tune dependent resonances are not included• Beam-beam tune shift might see other limits

Model of Beam-beam Parameter Versus Bunch Current:


Unperturbed vertical emittance εy = 108 pmBeam-beam limit ξy = 0.115

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 200 400 600 800 1000

Ver

tical

bea

m-b

eam

par

amet

er

Bunch current [µA]

98 GeV

Example from 98 GeV:


0.15

0.2

0.25

0.3

0.35

350 400 450 500 550 600 650 700 750

Ver

tical

em

ittan

ce [n

m]

Bunch current µA

LuminosityBEXE (e-)

Fitted single bunch emittance

Clear beam-beam blowup of 50-100%!(consistently observed from x-ray synchrotron radiation and luminosity)

Emittance blow-up for fill in 1998:


Unperturbed vertical emittance εy = 82 pmBeam-beam limit ξy = 0.111

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 200 400 600 800 1000

Ver

tical

bea

m-b

eam

par

amet

er

Bunch current [µA]

101 GeV

Example From 101 GeV


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 1 2 3 4 5

ξ y

Bunch current mA

October

July

August

Fitted asymptotic ξy limit

Similar Asymptotic Limits Suggested


Energy Damping decrement δ BB-limit

45.6 GeV 3.5e-4 0.045

101 GeV 3.8e-3 0.115

Scaling:

VLLC33 (δ = 0.01):

0.4yξ δ∞ ∝

0.17yξ∞ ≈ Total tune shift still

smaller than in LEP(4 IP’s)

Exponent 0.40 instead of 0.27!

(0.056 for VLLC34 with δ = 6e-4)

Predictions


From model get the luminosity incl BB:

In the BB limit:

For a given BB limit, the increase of luminositywith current is proportional to the energy γ(el.-magn. field of beam scales as 1/γ)

( )

2

* 22b

y

b

be

i

ir BeL

A

n γβ

= ⋅

+ ⋅

*2b

ye y

bnr

L ie

γ ξβ

∞ = ⋅ ⋅

Use model to predict luminosity:


Compare BB fit to luminosity data: 98 GeV

• Very well described• Simple “squared scaling” not adequate

0

50

100

150

200

250

300

350

0 200 400 600 800 1000

Lum

inos

ity [1

030 c

m-2

s-1

]

Bunch current [µA]


What happens for emittance (unperturbed) improvement:

0

50

100

150

200

250

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Lum

inos

ity [1

030 c

m-2

s-1

]

Vertical emittance [nm]

With BB limit

No BB limit

(unperturbed)

99 98

DFSlimit

(6 mA current)

LEP luminosity limit due to beam-beam: 2.0 1032 cm-2 s-1

(expected at maximum possible current)

(unperturbed)

(8 mA current)

0

50

100

150

200

250

300

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Lum

inos

ity [1

030 c

m-2

s-1

]

Vertical emittance [nm]

With BB limit

No BB limit


Optimisation

• Horizontal beam size given by synchrotron radiation and optics• Working point – beam-beam • Vertical emittance

– Coupling, global & local– Residual dispersion - golden orbits and dispersion free steering

• Vertical beam size at interaction point:– β*

X and β *y

– Dispersion at IP

Thereafter: Reproducibility


Vertical emittance:1999/2000: βy

* = 5 cm ( )2rmsy xyC D KEε ε∝ ⋅ ⋅ + ⋅ +K

E∝ (solenoids)

• Initial tuning of coupling, chromaticity, orbit, dispersion, …• Vertical orbit to get smallest RMS dispersion• Coupling to get smallest global coupling• Local dispersion, coupling, β-function at IP

“Golden orbit” strategy for optimization: Trial and error! Complement with:

Dispersion-free steering (DFS): 1) Measure orbit and dispersion2) Calculate correctors to minimize both

Peak luminosity}}

Note: Global correction generally also improves local dispersion/coupling!

Luminosity balance


-4

-2

0

2

4

0 100 200 300 400 500

y [m

m]

BPM number

-40

-20

0

20

40

0 50 100 150 200 250 300

θ y [µ

rad]

Corrector number

ORBIT DISPERSION CORR. KICKS

DFS: Simultaneously optimize orbit, disp., corr.

-4

-2

0

2

4

0 100 200 300 400 500

y [m

m]

BPM number

-15

-10

-5

0

5

10

15

0 100 200 300 400 500

Dy

[cm

]

BPM number

-15

-10

-5

0

5

10

15

0 100 200 300 400 500

Dy

[cm

]

BPM number

-40

-20

0

20

40

0 50 100 150 200 250 300

θ y [µ

rad]

Corrector number

Measured single beam performance of DFS in LEP:

(same algorithm as implemented for the SLC linac)


00.10.20.30.40.50.60.70.80.9

1

0 1 2 3 4 5 6

ε y [n

m]

Dy (rms) [cm]

1999 1998

98 GeV

0

0.2

0.4

0.6

0.8

1

4500 5000 5500 6000 6500 7000

Ver

tical

em

ittan

ce [n

m]

Fill number

1998

1999

(Data 500-550 µA)

Reduction of RMS dispersion

E [GeV]

94.5

96

98

100

101

Reduction ofvertical emittance

Emittance ratio: 0.5%

(simulated)

(DFS + change of separation optics)

19992000

1998

Vertical optimization


Damping partition number Jx used to reduce horizontal beam size σx:

Good for luminosity and backgrounds in experiments…

Jx controlled with RF frequency fRF.

∆fRF = 0 Hz Jx = 1.00∆fRF = 100 Hz Jx = 1.55 ∆Emax = - 0.7 GeV

Pay with reduction of maximum beam energy.

In 2000: Keep RF frequency shift small (~ -50 to +20 Hz).

(ii) Choice of RF frequency:

/ rmsxx x x x xJ D Eβ εσ β∝ ⋅= ⋅ Increase with

beam energy.


(E.g. H. Burckhardt, R.Kleiss. Beam Lifetimes in LEP. EPAC94)

05

101520253035404550

18:0018:00 19:0019:00 20:0020:00 21:0021:00Li

fetim

e [h

]

Time

ElectronsPositrons

Lifetime withoutcollision

Putting intocollision

Lifetime during collision(increase with current decrease)

Different regimes:

1) Without collision:Lifetime τ0 due to particles lost in Compton scatteringon thermal photons, beam-gas scattering.We assume 32 hours.

2) In collision:Lifetime due to particles lost in radiative Bhabha scatt.or beam-beam bremsstrahlung.

LEP lifetime without surprises:


Formulas in convenient units for LEP2 parameters (94.5 GeV):

−⋅⋅=−−

][1

][1][2.671]10[

0

1230

hhmAiscmL bunch ττ

BCT][3

1hy τ

ξ⋅

≈

30

35

40

45

50

55

19:00 19:05 19:10 19:15 19:20 19:25 19:30

Lum

. [10

30 c

m-2

s-1

]

BCT

40

45

50

55

60

19:00 19:05 19:10 19:15 19:20 19:25 19:30

Lum

. [10

30 c

m-2

s-1

]

Time

ALEPH DELPHI OPAL

Luminosity decay

Load new orbit + cancel

Correctorbitdrift

Optimizevert. tune

No effect from tails, resonances, …

Lifetime at High Energy Used As Fastest Luminosity Signal:


Operations

• Standard techniques:– Measure & correct beta*– Beta beating, coupling…– Essential, of course, good diagnostics, established measurement

techniques: Q-loop, Fast displays of lifetimes, beam sizes, Orbit feedback, Bunch current equalisation

• First years:– Lack of basic high-level control facilities– Poor data management– Interfaces to crucial beam instrumentation missing in control room– Poor and unreliable, incoherent data acquisition systems


time

Year Recover[min]

Filling[min]

Ramp /Squeeze[min]

Adjust[min]

Total[min]

# fills

1998 23.9 45.0 22.3 19.1 110.3 4361999 22.2 30.9 23.9 15.5 92.5 6532000 12.9 23.5 12.7 15.9 65.0 344Diffe-rence -9.3 -7.4 -11.2 +0.4 -27.5

Average turn-around time improved by ~ 28 minutes!

Typical 2000 turn-around: ~ 45 minutes

Lesscurrent

Twice theramp speed

BFSFasterdegauss,optimizeprocedure

Optimization of Turn-around

Reproducibility


Hardware• Specialised groups: power converters, RF, beam

instrumentation, kickers, separators, vacuum, dedicated expertise (electronics, controls, hardware)

• Over designed? Possibly but all hardware managed to withstand the extremely hard push to high energy

• Good availability with experience• Access system – always a problem

- Hardware performanceVacuum systemMagnetsPower suppliesInstrumentation etc

- Effects from LHC civil engineeringNo limiting effect on LEP operation (some realignment)

… excellent without major worries.


Improvements:

• Progressiveinstallation ofadditional RF cavities

• Increase accele-rating gradient

Beam energy follows available RF voltage…

0

500

1000

1500

2000

2500

3000

3500

4000

Jul-95 Feb-96 Aug-96 Mar-97 Sep-97 Apr-98 Nov-98 May-99 Dec-99 Jun-00 Jan-01

Date

RF

volta

ge [M

V]

65

75

85

95

105

115

125

Cryogenicsupgrade

Beamenergy

Nominal RFvoltage

Available RF voltage

Beamenergy[GeV]

RF voltage (design and actual):


- Background in the experiments:

RF frequency shift reduced foroptimization of energy reach

Larger horizontal beam sizePotentially larger backgrounds

Higher beamenergy

New optics in P4 and P8to help reducing background

Steady state conditions: Very good. Required continuous follow-up oncollimators, orbit, tunes, … Qh > 0.33 required

Occasional spikes: RF trips with negative RF frequency shiftRelated current loss

6) Other issues:


LEP 2000 preparation: 105 GeV (optics, power supplies, etc checked)

Gain from 1999 physics to 2000:

5b) Energy increase of LEP from 1999 to 2000:

RF system

Operationalprocedures

Reduced luminosity production, potentially higher backgrounds

8 additional Cu RF units + 0.14 GeVHigher RF gradient + 0.96 GeVLess RF margin + 1.50 GeVReduced RF frequency + 0.70 GeVBending length + 0.20 GeVTotal + 3.50 GeV

Maximum energy: 101.0 GeV ⇒ 104.4 GeV

Improvements:


LEP operated in “discovery mode”:

Beam energy increased by 3.4 GeV• Increase of RF voltage (3650 MV), excellent stability• Change of operational strategy (ramp during physics fill, …)• Reduced shift of RF frequency• Increase of average bending radius

Push beam energy on cost of luminosity• Reduce beam current (5 mA instead of 6.2 mA)• Run with small Jx, large horizontal beam size• Mini-ramp to quantum lifetime limit

(zero margin in RF voltage)• Lose all fills with RF trips

Luminosity production rate lower than 1999 but still excellent (as in 1998)Luminosity improvement in 1999 with better tuning: + 20 %Price to pay for energy increase in 2000: - 20 %

2000 was the second productive LEP year

2000: conclusions


Unique at LEP:

Large range of energies 22 GeV to 104.5 GeVPolarization studied from 41 GeV to 98.5 GeV

Explore spin dynamics in unique regime

Bench marking of theoretical predictions

Sharp drop-off!

E [GeV]

P [%

]

LEP1

TRISTAN

HERAPETRA

VEPP4, DORIS II, CESR

SPEAR

VEPP-2M, ACO

LEP2

0

25

50

75

100

0 10 20 30 40 50 60 70 80 90

With...Without...

Harmonic Spin Matching

Transverse spin-polarization in LEP


Precise determination of the LEP beam energy (10-5 relative accuracy, ~ 1 MeV)Precise measurement of the Z mass and width

∆ E

[M

eV]

11. November 1992

∆ E

[M

eV]

29. August 1993

Daytime

11. October 1993

-5

0

5

23:00 3:00 7:00 11:00 15:00 19:00 23:00 3:00

-5

0

5

11:0

0

13:0

0

15:0

0

17:0

0

19:0

0

21:0

0

23:0

0

18:0

0

20:0

0

22:0

0

24:0

0

2:00

4:00

6:00

8:00

Axis of earth rotationCERN, Geneva

Moon

Ecliptic

Small changes of energy accurately measured(energy change from 1mm circumference change)

Use of Polarization at LEP:


MeV6486.440E

=ν 519109.31 ντ

λ ⋅⋅== −

p

6 26.67 10E

Eνσσ ν ν−= ⋅ ≈ × ⋅

( )

2 22

22 2,

( / )1118

k mp

k md

w T

k m

γ

γ γ

ντν

τ ν ν ν

∆=

− − −

∑

−⋅

= 2

2

2

22

2exp

2 γ

ν

γ

ν

νσ

νσ

mm IT

13

2

<<=γνλναCondition for correlated

spin resonance passings:true

Spintune

Polarizationbuildup rate

Spin tunespread

Theory by Derbenev, Kontratenko, Skrinsky (With LEP Parameters):

Synchrotron tune γν

Resonance strength 2102 1094.1 ν⋅×≈ −kw

P [%

]

E [MeV]

440 MeV

ν

N

σE = 31 MeV (LEP I)

σE = 51 MeV (DWIG)

σE = 125 MeV (LEP II)

0

10

20

30

40

50

60

70

80

44400 44500 44600 44700 44800 44900 45000

0

0.2

0.4

0.6

0.8

1

100.75 101 101.25 101.5 101.75 102 102.25

SITFSODOMsimulations


0

10

20

30

40

50

60

35 40 45 50 55 60 65 70 75 80

Pol

ariz

atio

n [%

]

Energy [GeV]

SITF simulations (50 seeds)

τp/τd = (ν/88)4

τp/τd = (ν/95)2

First order theory: Includes spin resonances with kx, ky, ks=1

Nkkkkkkk syxssyyxxdepol ∈⋅±⋅±⋅±= ,,,νννν

Machine tunes

Synchrotron sidebandsdetermine polarizationdegree in LEP

Simulation confirms 1/E4

dependence of polarization!

Energy Dependence of Polarization:


0

10

20

30

40

50

60

70

80

40 50 60 70 80 90 100

Pol

ariz

atio

n [%

]

Energy [GeV]

Linear

Higher order

Measurements• With 90/60, 60/60 and 102/45 optics.

• Goal for energy calibration: > 5%

• Polarization not always fullyoptimized.

1998: Polarization and energy calibrationhas been extended to 60.6 GeV (P = 7% measured)!

Drop in polarization degree consistent with higher-order theory…

Polarization Measurements in LEP:


44.7 45.0 47.0 51.3 57.4

Equivalent E [GeV]

Higher-order

Linear

Bl [Tm]

P ∞ [

%]

0

10

20

30

40

50

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Wigglers increase spin tune spread and thus allow “simulating” energy increase...

Higher-Order Theory also Confirmed with Wigglers:


With: 26

GeV44065.01076.6

⋅⋅= − E

νσ• LEP enters uncorrelated regime with high

energy and small Qs!

• If spin resonance passing is uncorrelatedit is completely uncorrelated for LEP!

• We can stay in the correlated regime byincreasing the value of Qs!

Evaluate Correlation Criteria for LEP:


MeV6486.440E

=ν 519109.31 ντ

λ ⋅⋅== −

p

6 26.67 10E

Eνσσ ν ν−= ⋅ ≈ × ⋅

( )

2 22

22 2,

( / )1118

k mp

k md

w T

k m

γ

γ γ

ντν

τ ν ν ν

∆=

− − −

∑

−⋅

= 2

2

2

22

2exp

2 γ

ν

γ

ν

νσ

νσ

mm IT

13

2

<<=γνλνα γν νσ >>

[ ]

24 22

3 2

108 exp( 2 )11 154 11

p

d

w νν

τ σπ ντ π π ν λ

− −= ⋅ ⋅ ⋅ +

2p k

d

wτ πτ λ

=

1<<νσ

Condition for correlatedspin resonance passings:

true

true

false

false

Condition for completeuncorrelation

true

Spintune


Spin tunespread



Theory by Derbenev, Kontratenko, Skrinsky (with LEP

parameters):


Expected polarization: Very low, but possible increase at high energies?

New polarization optics (101.5/45 degrees) for measurements at low AND high energy

60.6 GeV 4 % (7% with 60/60 optics)70.0 GeV < 1%92.3 GeV < 1%98.5 GeV < 1%

No indication of measurable polarization at highest LEP energies!(first measurements in regime of uncorrelated crossings of spin resonances)

Search for Polarization at Highest LEP Energies:


E [GeV]P

[%]

LEP1

TRISTAN

HERAPETRA

VEPP4, DORIS II, CESR

SPEAR

VEPP-2M, ACO

LEP2

0

25

50

75

100

0 10 20 30 40 50 60 70 80 90

With...Without...

Harmonic Spin Matching

Transverse spin polarization inhigh energy regime measured.(way above previously assessed regime)

Sharp drop after LEP1 in agreementwith theory/simulations.

Transverse spin polarization crucialfor precision measurements of theW and Z properties (energy calibration)

First measurement in regime of uncorrelated spin resonance crossing.No sign of transverse polarization.

New varieties of Harmonic SpinMatching gave up to 57% polarization.

We can trust the polarization theories in LEP regime!

Precise predictions for future projects…

Achievements at LEP:


MeV6486.440E

=ν 21 51 8.7 10p

λ ντ

−= = ⋅ ⋅

6 22.4 10E

Eνσσ ν ν−= ⋅ ≈ × ⋅

( )

2 22

22 2,

( / )1118

k mp

k md

w T

k m

γ

γ γ

ντν

τ ν ν ν

∆=

− − −

∑

−⋅

= 2

2

2

22

2exp

2 γ

ν

γ

ν

νσ

νσ

mm IT

13

2

<<=γνλναCondition for correlated

spin resonance passings:true

Spintune


Spin tunespread

Theory by Derbenev, Kontratenko, Skrinsky (With VLLC33 Parameters):



Build-up time τp: 1.9 h

Spin tune ν: 417.5

Spin tune spread σν: 0.42

Synchrotron tune: 1/7


What does this mean for VLLC?

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Pol

ariz

atio

n [%

]

Energy [GeV]

LinearLEP HO

VLLC33 HOMeasurements

Large spin tune spread Enhancement of depolarization(as in LEP at high energy)


P [%

]

E [MeV]

440 MeV

ν

N

σE = 31 MeV (LEP I)

σE = 51 MeV (DWIG)

σE = 125 MeV (LEP II)

0

10

20

30

40

50

60

70

80

44400 44500 44600 44700 44800 44900 45000

0

0.2

0.4

0.6

0.8

1

100.75 101 101.25 101.5 101.75 102 102.25


Linear / higher-order theory for different Qs…

Qs = 0.2: Expect sufficient polarization up to 80-85 GeV!

Raising Qs improvespolarization for high energies!

Why?Imagine Qs = 1

Qs satellites overlayinteger resonances

(ν = k + i · Qs)

High Qs for LEP


0

10

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50

60

40 60 80 100 120 140 160 180 200

Pol

ariz

atio

n [%

]

Energy [GeV]

Ultra-highenergy

Qs = 1/5Higher-order theory

5 %

Uncorrelated passingsof spin resonances

(small Qs)

Spin tune spreadσν >> 1

(probably not true at 100 GeV)

Theory predicts: Polarization comes back at ultra-high energies!

Why? Fast increase of polarization build-up, increase in depolarization slows down!

Very uncertain regime (who knows what really happens)…

Polarization increase at Ultra-high energies:


Strong transverse damping: Very nice beam dynamics regime (performance)

- Less tails- Less effects from resonances (we can jump them)- Ramp colliding beams at high energy- Higher beam-beam limitTwo thirds of all LEP luminosity collected in the last 3 years (out of 10.5y)

LEP data would indicate a beam-beam limit of 0.17 for VLLC33.

Optimization of vertical orbit to the limit (dispersion/coupling correction for LEP)

Need operational overhead in RF voltage (>= 6 % in LEP) - optimize # klystrons

Do not expect significant radiative spin-polarization (even linear level is very low)

Some preliminary thoughts:


Sociology

• Good support from equipment groups, good motivation, close interaction with machine in-house expertise.

• Common control room – operations as focus for machine physicists, equipment groups and experiments.Regular informal contact at all levels.

• Comprehensive annual workshops - Chamonix.• Cross-fertilisation from other labs.• Stimulated by close contact with experimental physicists.• Makeup of operations. Ph.Ds on shift

lep operation and performance - cornell university...65.0 0.050 249 91.5 0.055 89 94.5 0.075 81 98.0...

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