1 / 25

Contributions to the Beam Lifetime

Contributions to the Beam Lifetime. John T. Seeman SLAC Hawaii Super-B-Factory Workshop January, 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.

errol
Download Presentation

Contributions to the Beam Lifetime

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Contributions to the Beam Lifetime John T. Seeman SLAC Hawaii Super-B-Factory Workshop January, 2004

  2. 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-g) • Beam-beam tune shift

  3. 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 • by* = 12 mm • bx* = 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

  4. Advanced B Factory with 952 MHz RF Frequency • E+ = 8 GeV • E- = 3.5 GeV • I+ = 10.1 A • I- = 23.0 A • by* = 1.5 mm • bx* = 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.

  5. 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.

  6. PEP-II LER Touschek Estimate

  7. Recent: PEP-II LER Touschek Lifetime U. Wienands [J. LeDuff formula]

  8. Touschek lifetime versus RF voltage Smaller bunches Quantum lifetime

  9. 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 sz (x0.2) • Energy change g (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.

  10. Luminosity lifetime (e+e- --> e+e-g) • Luminosity lifetime from particle losses from collisions. s = 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.

  11. Fast Luminosity Monitor Luminosity signal e+e--> e+e-g g Beam loss monitors placed here have measured the luminosity.

  12. 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)

  13. PEP-II Betatron Tune Locations LER HER New tunes Old tunes Old tunes New tunes

  14. 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

  15. Lifetime for 1035 luminosity

  16. Lifetime for 1036 luminosity

  17. Lost particles per second and power loss Without beam-beam tune shift lifetime.

  18. 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.

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

  20. IR betas for HER and LER LER beta functions HER beta functions

  21. Luminosity enhancement at very small crossing angles PEP-II simulation (Cai) Enhancement only appears at high beam-beam parameters. 0 and 0.75 mrad L Lsp KEKB simulation (Ohmi) I+*I- Experiments on PEP-II planned but not yet done.

More Related