BeamBeam Collimation Study Stephanie Majewski Witold Kozanecki with

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

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 PR 02 collimators downstream of the IP

Input Parameters x [mm] x’ [mrad] y [mm] y’ [mrad] e/nominal Nominal Beam 0. 105 0. 210 0. 00477 0. 313 1 “Large” X-Emittance 3. 15 6. 29 0. 00477 0. 313 900 in x “Large” Y-Emittance 0. 105 0. 210 0. 477 31. 3 10000 in y ex (nominal) = 22 nm-rad ey (nominal) = 1. 49 nm-rad 3

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

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

solid arrows x dashed arrows y [m] -2095 m -3. 6 m IP -1900 m -2118 m -2042 m -1600 m -1325 m Z [m] IP Ø Ø colors of arrows/text correspond to lost particle locations plotted on slides 4 & 5 numbers are TURTLE coordinates 6

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

X Distribution at Movable Jaw X Collimator, -12 m from IP Closing PRO 4 Collimators X [mm] minimal aperture X [mm] current setting 10 sigma setting 8

Collimator Locations LER 9

X Distribution at Movable Jaw X Collimator, -25 m from IP particles that hit within ± 25 m of IP Closing PRO 4 Collimators X [mm] minimal aperture X [mm] current setting 10 sigma setting 10

+25. 2 m from IP LER -25. 2 m from IP X [mm] x x [m] x [2 ] +25 m -13. 6 54. 2 0. 0 -25 m +13. 6 54. 2 37. 11 Results are based on an older LER deck (’ 98) with a tune of 0. 57 (in x). X [mm]

Summary • Large-amplitude, horizontal -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 PR 04 collimators in some corners of phase space provides no protection against Coulomb scatters between PR 04 and PR 02 preferable to maintain collimation capability at -25 m

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 PR 04 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

Spares 14

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

solid arrows x dashed arrows y [m] IP QD__ near SCY 3 Q 2 QFS 3 L before QD 34 QF__ QF 3 R 01 QF 4 R 01 QFPR 12 QF__ before SCX 3 QF__ Z [m] IP colors of arrows/text correspond to lost particle locations plotted on slides 4 &5 Ø Ø labels are MAD/TURTLE elements 16

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

solid arrows x dashed arrows y QDI_ near DSEP [m] QFI_ near DIDF, DM 1 BFF QFI_ near DM 1 BFF, DM 1 AFF colors of arrows/text correspond to lost particle locations plotted on slides 4 &5 Z [m] Ø Ø labels are MAD/TURTLE elements 18

Collimator Locations PEP-II Regions Map HER LER 19

10 based on fully-coupled vertical emittance, wiggler on: ex = 48 nm-rad, ey = 24 nm-rad PR 02 PR 04 LER Collimator Apertures Collimator Distance from IP Spring 04 Setting 8 s 10 s 12 s Primary Y 3014 -365 m y ≥ -10. 5 mm y ≥ -6. 8 mm y ≥ -8. 5 mm y ≥ -10. 2 mm Primary X 2082 -345 m x ≤ 11. 8 mm x ≤ 8. 9 mm x ≤ 11. 1 mm x ≤ 13. 3 mm Secondary X 2042 -320 m x ≤ 8. 4 mm x ≤ 6. 5 mm x ≤ 8. 1 mm x ≤ 9. 7 mm Secondary Y 2032 -313 m y ≤ 6. 3 mm y ≤ 5. 5 mm y ≤ 6. 9 mm y ≤ 8. 3 mm Movable Jaw 3076 -25 m x ≥ -19. 5 mm x ≤ 22. 0 mm |x| ≤ 18. 9 mm Movable Jaw 3043 -12 m x ≥ -27. 5 mm x ≤ 26. 0 mm |x| ≤ 17. 4 mm *** Note: These are TURTLE sign conventions (+x = toward inside of ring for LER) 20

+12. 5 m from IP LER -12. 5 m from IP X [mm] x x [m] x [2 ] +12 m -11. 9 46. 1 0 -12 m 46. 1 38. 11 11. 9 Results are based on an older LER deck (’ 98) with a tune of 0. 57 (in x). X [mm]

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

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

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

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? 25

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

First-Order MAD Calculation x x [m] x [2 ] +25 m -13. 6 54. 2 0. 0 -25 m +13. 6 54. 2 37. 11 -13. 6 54. 2 38. 57 +13. 6 54. 2 75. 71 -13. 6 54. 2 77. 14 (+1 turn) +25 m (+1 turn) -25 m (+2 turns) +25 m (+2 turns) 27