Beam-Beam Collimation Study

1. Beam-Beam Collimation StudyStephanie Majewski, Witold KozaneckiAccelerator Physics meeting, 17 Sep 2004 • with thanks to • J. Va’vra, for a bright idea! • R. Barlow & T. Fieguth, for help with Turtle

2. Strategy • NOT a beam-beam simulation • Use TURTLE • Generate a large-emittance beam (first in x, then in y) that fills the phase space at the IP • This is the naïve equivalent of a multi-turn calculation • Simulate tightening existing collimator apertures • Explore moving existing PR02 collimators downstream of the IP

3. Input Parameters ex (nominal) = 22 nm-rad ey (nominal) = 1.49 nm-rad

4. Large X-Emittance: Phase Space Plot Starting x, x’ coordinates of particles lost along the beamline. x’/x; x/x Z location where particles are lost. Colors correspond to upper plot. Z [m] IP IP

5. Large Y-Emittance: Phase Space Plot Starting y, y’ coordinates of particles lost along the beamline. y’/y; y/y Z location where particles are lost. Colors correspond to upper plot. -2095 m No particles hit near IP -135 m -1101 m Z [m] IP IP

6. solid arrows  x dashed arrows  y  [m] IP -2095 m -3.6 m -1900 m -1600 m -2118 m -2042 m -1325 m Z [m] IP • colors of arrows/text correspond to lost particle locations plotted on slides 4 & 5 • numbers are TURTLE coordinates

7. -12m collimator (3043/304) Near-IP losses (LER)

8. X Distribution at Movable Jaw X Collimator, -12 m from IP X [mm] X [mm] Closing PRO4 Collimators X [mm] X [mm] minimal aperture current setting 10 sigma setting

9. Collimator Locations LER

10. X Distribution at Movable Jaw X Collimator, -25 m from IP particles that hit within ±25 m of IP X [mm] X [mm] Closing PRO4 Collimators X [mm] X [mm] minimal aperture current setting 10 sigma setting

11. +25.2 m from IP LER -25.2 m from IP X [mm] Results are based on an older LER deck (’98) with a tune of 0.57 (in x). X [mm]

12. Summary • Large-amplitude, horizontal b-tron tails originating at the IP can be effectively curtailed at + 25 m • ...at least in the simulation • basically because of the phase-advance relationships reduce this to a one-turn problem, and assuming the impact on LEB lifetime remains manageable. • This study will be redone with the new LER deck & current x-tune of 0.51. • Vertical tails are not an issue (in the LER) • Pre-trickle collimator-scan data remain to be analyzed. • However, the +25 m collimator • can’t replace existing PR04 collimators in some corners of phase space • provides no protection against Coulomb scatters between PR04 and PR02 •  preferable to maintain collimation capability at -25 m

13. Conclusions • Original recommendation • Move -12 m collimator to +25 m • Keep -25 m collimator in current location Step 1: Leaving the -25 m collimator allows flexibility in collimation and complements PR04 Step 2: If successful, consider removing -25 m collimator in future to reduce HOM heating • In practice • both the –25 & the –12 m collimator are scheduled for removal during the 2004 shutdown, to help alleviate the HOM-heating problem • one of these collimators (-12 m preferred) will be moved to +25 m during a subsequent shutdown

14. Spares

15. Compare Loss Points with LER Beta Functions  [m] IP Z [m]

16. solid arrows  x dashed arrows  y  [m] QF__QF3R01QF4R01QFPR12 IP QD__ near SCY3 Q2 QF__ QFS3L before QD34 QF__ before SCX3 Z [m] • colors of arrows/text correspond to lost particle locations plotted on slides 4 &5 • labels are MAD/TURTLE elements IP

17. solid arrows  x dashed arrows  y -1101 m  [m] -1075 m -1125 m Z [m] • colors of arrows/text correspond to lost particle locations plotted on slides 4 &5 • numbers are TURTLE coordinates

18. solid arrows  x dashed arrows  y QDI_ near DSEP  [m] QFI_ near DM1BFF, DM1AFF QFI_ near DIDF, DM1BFF Z [m] • colors of arrows/text correspond to lost particle locations plotted on slides 4 &5 • labels are MAD/TURTLE elements

19. Collimator Locations PEP-II Regions Map LER HER

20. 10 s based on fully-coupled vertical emittance, wiggler on:ex = 48 nm-rad, ey = 24 nm-rad LER Collimator Apertures PR04 PR02 *** Note: These are TURTLE sign conventions(+x = toward inside of ring for LER)

21. +12.5 m from IP LER -12.5 m from IP X [mm] Results are based on an older LER deck (’98) with a tune of 0.57 (in x). X [mm]

22. X Distribution at Proposed Collimator Location, +12 m from IP X [mm] X [mm] X [mm] X [mm] minimal aperture 10 sigma setting

23. X Distribution at Proposed Collimator Location, +25 m from IP X [mm] X [mm] X [mm] X [mm] minimal aperture 10 sigma setting

24. Consistency Check – Compare w/ Durin (0 m = IP) Coulomb Scattering Z [m] Z [m] Coulomb Scattering Z [m] Z [m] Coulomb Scattering Z [m] Z [m] Coulomb Scattering 12 & 25 m collimators closed Z [m] Z [m]

25. Multi-Turn Extrapolation • TURTLE only simulates one turn • Caveat: Following results use a LER deck with a tune of 0.57 • Do these results make sense for a storage ring?

26. Plots include all particles produced Starting Point: +25 m X’ [mrad] Y’ [mm] Y’ [mrad]

27. First-Order MAD Calculation

28. Plots include all particles produced TURTLE/Calculation Comparison Calculation starting point X’ [mrad] X [mm] X [mm] X [mm] X [mm] X [mm]

29. Plots include all particles produced Direct Comparison TURTLE X[mm] TURTLE X[mm]

30. Plots include all particles produced Correlation Check X’ [mrad] at +25 m Y’ [mrad] at +25 m