J. SeemanJanuary 2004

SLAC Accelerator Department

Contributions to the Beam Lifetime

John T. SeemanSLAC

Hawaii Super-B-Factory WorkshopJanuary, 2004

SLAC Accelerator Department

J. SeemanJan 2004

Lifetime Effects• Quantum lifetime

– (Not a problem as the RF voltage is high.)• Residual gas

– Bremsstrahlung – Elastic scattering– Small change as the gas is only a few times worse.

• Touschek effect• Luminosity

– Bhabha (e+e- e+e-) – Radiative Bhabha (e+e- e+e-)

• Beam-beam tune shift

SLAC Accelerator Department

J. SeemanJan 2004

Present PEP-II B Factory with 476 MHz RF Frequency

• E- = 9 GeV• E+ = 3.1 GeV• I- = 1.2 A• I+ = 1.8 A y

* = 12 mm x

* = 30-50 cm• Bunch length = 12 mm• Crossing angle = 0 mrad• Beam-beam parameters = 0.06-0.09• N = 1317 bunches• L = 7.2 x 1033 cm-2s-1

SLAC Accelerator Department

J. SeemanJan 2004

Advanced B Factory with 952 MHz RF Frequency

• E+ = 8 GeV• E- = 3.5 GeV• I+ = 10.1 A• I- = 23.0 A y

* = 1.5 mm x* = 15 cm• Bunch length = 1.8 mm• Crossing angle = ~15. mrad• Beam-beam parameters = 0.115• N = 6900 bunches• L = 1 x 1036 cm-2s-1

• Site power with linac and campus = ~120 MW.

SLAC Accelerator Department

J. SeemanJan 2004

SLAC Accelerator Department

J. SeemanJan 2004

SLAC Accelerator Department

J. SeemanJan 2004

Vacuum lifetimes

• At PEP-II the LER vacuum lifetime is about 6 hours at 2 amps. The HER vacuum lifetime is about 12 hours at 1 amp.

• Extrapolating the lifetime to a Super B-Factory, we assume ten times the radiation and, thus, ten times the gas generation and three times the pumping/outgassing rate.

• Therefore, the vacuum lifetimes will be about three times worse or 2 hours in the LER and 4 hours in the HER.

SLAC Accelerator Department

J. SeemanJan 2004

PEP-II LER Touschek Estimate

SLAC Accelerator Department

J. SeemanJan 2004

SLAC Accelerator Department

J. SeemanJan 2004

Recent: PEP-II LER Touschek LifetimeU. Wienands

[J. LeDuff formula]

SLAC Accelerator Department

J. SeemanJan 2004

Touschek lifetime versus RF voltage

Quantumlifetime

Smallerbunches

SLAC Accelerator Department

J. SeemanJan 2004

Touschek lifetime• Large angle-single-scattering events

which change the scattered particle momentum sufficiently to make it fall outside the momentum acceptance of the accelerator.

• Changed issues:– Higher bunch currents I (x10)– More bunches n (x4)– Shorter bunches z (x0.2)– Energy change (3.1 3.5) (x1.37)N increases from 2A to 20 A in the

LER and 1 A to 10 A in the HER. The number of bunches increase a

factor of 4.The bunch lengths are reduced from

10 mm to 2 mm.Thus, the Touschek lifetimes decrease

by a factor of 10 to 13. The LER Touschek is reduced from 7 hours to 46 mins. The HER Touschek lifetime is reduced from 100 hours to 6 hours.

zTouschek nI

6.2

,

~1

SLAC Accelerator Department

J. SeemanJan 2004

SLAC Accelerator Department

J. SeemanJan 2004

Luminosity lifetime (e+e- --> e+e-

• Luminosity lifetime from particle losses from collisions. = 3 x 10-25 cm-2.

• At L = 1036, dN/dt=3.0 x 1011/s = 2.2 x 106/turn.• N = 9 x 1014 or 1.3 x 1011/bunch for 20 A.• At 10A the lifetime is 25 min. At 20 A, 50 min.

)()( tLtdtdN

SLAC Accelerator Department

J. SeemanJan 2004

e+e- eeLuminosity signal

Fast Luminosity Monitor

Beam loss monitors placed here have measured the luminosity.

SLAC Accelerator Department

J. SeemanJan 2004

Can lifetime be traded for beam-beam parameter? Beam-beam lifetime

• The accelerator operators often trade beam lifetime for luminosity (i.e. tune shift) by pushing the tunes.

• Here the horizontal tune was changed by -0.002 which lowered the LER lifetime from 165 minutes to 65 minutes but gained over 3% in luminosity. The tune was then restored before the fill was lost.

• This effect has not been studied in detail. More studies to follow.

Luminosity

Time (10 min)

SLAC Accelerator Department

J. SeemanJan 2004

PEP-II Betatron Tune Locations

Old tunes

LER HER

New tunes

New tunes Old tunes

SLAC Accelerator Department

J. SeemanJan 2004

PEP-II operates in a beam-beam limited regime

Luminosity vs I+I- Specific Luminosity vs I+I-

I+I- I+I-

Beam-beam parameter limit Background/lifetime limit

SLAC Accelerator Department

J. SeemanJan 2004

Lifetime for 1035 luminosityLifetime contribution

HER lifetime (min)

LER lifetime (min)

Quantum 3000 6000

Vacuum 360 180

Touschek 923 110

Luminosity 75 150

Beam-beam tune shift

30 30

Total life w/o b-b 57 47

Total life with all 20 18

SLAC Accelerator Department

J. SeemanJan 2004

Lifetime for 1036 luminosityLifetime contribution

HER lifetime (min)

LER lifetime (min)

Quantum 3000 6000

Vacuum 240 120

Touschek 360 45

Luminosity 25 50

Beam-beam tune shift

20 20

Total life w/o b-b 21 20

Total life with all 10 10

SLAC Accelerator Department

J. SeemanJan 2004

Lost particles per second and power loss

Luminosity HERParticles lost per second

HER Power loss

(kW)

LER Particles lost per second

LERPower loss

1035 4.4x1010 56 W 1.1x1011 62 W

1036 3.6x1011 461 W 7.5x1011 420 W

Without beam-beam tune shift lifetime.

SLAC Accelerator Department

J. SeemanJan 2004

Summary of contributions to the beam lifetime• Touschek, luminosity losses, and beam-

beam effects will dominate the lifetimes in the Super-B-Factories.

• 1035 beam lifetimes will be about 45 to 60 minutes without beam-beam.

• 1036 beam lifetimes will be about 20 minutes without beam-beam.

• The lifetimes will be reduce another factor of two if the beam-beam parameters are pushed hard.

SLAC Accelerator Department

J. SeemanJan 2004

Backup slides

• Interaction region beta functions• Luminosity gain from low crossing angles.

SLAC Accelerator Department

J. SeemanJan 2004

IR betas for HER and LER

HER beta functions LER beta functions

SLAC Accelerator Department

J. SeemanJan 2004

Luminosity enhancement at very small crossing angles

KEKB simulation(Ohmi)

PEP-II simulation (Cai)Enhancement only appears at high beam-beam parameters.

I+*I-

0 and 0.75 mradL

Lsp

Experiments on PEP-II planned but not yet done.