W. KozaneckiMCC AP meeting, 29 July 04  Goal: measure the luminosity degradation associated with  parasitic crossings  horizontal crossing angle  Principle  by-2 pattern: compare L sp at minimum, nominal & maximum parasitic- xing separation ( = e - x-angle) with full L optimization at each setting  sensitivity to Xing angle + parasitic crossings  by-4 pattern: compare L sp at minimum, 0, & maximum (achievable) Xing angles ( = e - x-angle) with full L optimization at each setting  sensitivity to Xing angle only  HEB only: measure impact (if any) of e - x-angle on e - beam properties W. Kozanecki, Y. Cai, W. Colocho, J. Seeman, M. Sullivan, J. Turner (with special thanks to Nate Lipkovitz & Cliff Blanchette) Beam-beam sensitivity to parasitic crossings & Xing angle

W. KozaneckiMCC AP meeting, 29 July 04 Experimental aspects (I)  Horizontal parasitic crossings  XP(e-) more +ve   X(PC)   nominal:  X(PC) = 3.22 z = +/- 63 cm  for XP max (e - ) = / mrad,  X  3.6 mm (+ 12%) / 2.7 mm (-17%) + x

W. KozaneckiMCC AP meeting, 29 July 04 Experimental aspects (II)  Quality/reproducibility of measurements  thermal / beam-beam effects  keep currents constant (total / per bunch)  sparsified by-2: 836 bunches, 1201/751 mA, 1.44/0.90 mA/b  by-4: 851 bunches, 1221/758 mA, 1.43/0.89 mA/b  trickle both beams  re-optimize L sp at each XP(e-) setting  tunes  local & global skews (both rings)  PR02 LER sext bumps (HER always, LER most of the time)  y-angle, collision phase (most of the time)

W. KozaneckiMCC AP meeting, 29 July 04 I. Measure L sp degradation associated with parasitic Xings + Xing angle Sparsified by-2 pattern, LER/HER = 1.4/0.9 mA/b  Setup  Set LER/HER YANG, SLM/interferometer light levels  In both LER & HER, optimize all local & global skews, PR02 SEXT bumps, SD2 bumps in LER Arcs 5 & 11, collision phase  Mini scan of XP(e - ) ( mrad) to locate optimum e - angle (XP opt = 0 )

W. KozaneckiMCC AP meeting, 29 July 04 L sp degradation with parasitic Xings + Xing angle L sp degradation with parasitic Xings + Xing angle (cont’d)  At XP = 0, + 850, - 600, - 300,  rad  Optimize LER+HER local & global skews, PR02 SEXT bumps  Optimize collision phase  Record tune spectra, gated camera data, L sp & I b +,- patterns along the train   20% degradation at  rad Investigated correlated variations in tunes & e + /e - spot sizes: no clear trend in LER/HER tune tracker readings (too few points compared to fluctuation size) no clear trend in LER SLM/interferometer sizes (fluctuations) definite trend in HER spot sizes

W. KozaneckiMCC AP meeting, 29 July 04 L sp degradation with parasitic Xings + Xing angle L sp degradation with parasitic Xings + Xing angle (cont’d)  At XP = 0, +850, - 600, -300,  rad  Optimize LER+HER local & global skews, PR02 SEXT bumps  Optimize collision phase  Record tune spectra, gated camera data, L sp & I b +,- patterns along the train   20% degradation at  rad

W. KozaneckiMCC AP meeting, 29 July 04 II. Measure L sp degradation associated with Xing angle only by-4 pattern, same LER/HER bunch currents  Setup  Skew quads/sext bumps already restored to XP=0 settings found in step I  Optimize tunes, collision phase (in case RF-transient is pattern-dependent)  Mini scan of XP(e - ) to check optimum e - angle (before further optimiation)  optimum XP very different (more +ve!)

W. KozaneckiMCC AP meeting, 29 July 04 L sp degradation with Xing angle only L sp degradation with Xing angle only (cont’d)  Optimize Luminosity at XP = +550, +850, - 600, 0  rad  note XP=0 is by definition the optimum e - angle found in the by-2 pattern  Even after  rad, L is higher at somewhat smaller XP(e-), and then drops again.  y - displays a corresponding trend.

W. KozaneckiMCC AP meeting, 29 July 04  Even after  rad, L sp is higher at larger XP(e-).  y - displays a corresponding trend. L sp degradation with Xing angle only L sp degradation with Xing angle only (cont’d)

W. KozaneckiMCC AP meeting, 29 July 04  Similar effect seen in previousXing-angle MD (by-4 pattern, 11 May 04) L sp degradation with Xing angle only L sp degradation with Xing angle only (cont’d)

W. KozaneckiMCC AP meeting, 29 July 04 L sp degradation with Xing angle only L sp degradation with Xing angle only (cont’d)  Optimize specific luminosity at XP = +550, +850, - 600, 0  rad  note XP = “0” is by definition the optimum e- angle found in the by-2 pattern  L sp > XP = “0”  7% degradation at  rad

W. KozaneckiMCC AP meeting, 29 July 04  Without parasitic Xings (by-4) L sp exhibits a parabolic dependence on XP(e-)  With parasitic Xings (by-2)  the peak L sp is ~ 5% lower nominal PC separation) than in the by-4 pattern  the larger XP(e-), the steeper the L sp degradation  The optimum e - x angle is ~ 0.2 mrad more -ve in the by-2 pattern (  weaker PC effects)  This suggests that in the presence of parasitic Xings, the optimum e - angle is a compromise between Xing-angle & PC-induced luminosity degradation L sp dependence on Xing angle & PC separation: experimental summary

W. KozaneckiMCC AP meeting, 29 July 04 L sp dependence on Xing angle & PC separation: data vs. simulations Simulation neglects Xing-angle effects

W. KozaneckiMCC AP meeting, 29 July 04 Related topics...  Parasitic crossings  how do the Pacman bunches fare?  what is happening in the long minitrain?  Crossing angle (w/o PC)  why do the HER optics vary (or appear to vary) with electron x-angle, even though there are non-linear elements inside the XP bump?

W. KozaneckiMCC AP meeting, 29 July 04 Parasitic crossings: how do the Pacman bunches fare? Sparsified by-2 pattern

W. KozaneckiMCC AP meeting, 29 July 04 Parasitic crossings: the dro o o o ping minitrain

W. KozaneckiMCC AP meeting, 29 July 04 e - x-angle response of L sp & HER beam sizes in collision Collisions, by-4 No optimization during scan Collisions, by-4

W. KozaneckiMCC AP meeting, 29 July 04 HEB x size (e - only, by-2) HEB y size (e - only, by-2) e - x-angle response of HER beam sizes Collisions, by-4

W. KozaneckiMCC AP meeting, 29 July 04 HEB y tune (e - only, by-2) HEB x tune (e - only, by-2) e - x-angle response of HER tunes Collisions, by-4

W. KozaneckiMCC AP meeting, 29 July 04 Summary (in words...)  In the by-4 pattern (where parasitic-crossing ing effects are expected to be negligible)  The specific luminosity exhibits a roughly parabolic dependence on the horizontal e - angle (after each angle). It degrades by ~ 6-7 % for an e - x-angle of ~ 650  rad above the optimum.  At the same angle, the simulation predicts a 3% degradation only. More generally, the crossing-angle dependence of the luminosity is significantly steeper in the data than in the simulation.  Systematic variations of the e - horizontal beam size and vertical tune, observed in e - x-angle scans recorded in collision, are also apparent, and of comparable magnitude, when varying the horizontal e - angle in single-beam mode. The large variations in vertical HEB spot size, observed in collision only, are strongly correlated with L sp variations and clearly of beam-beam origin.  Whether the horizontal spot size variation could be associated to image motion on the SLM screen remaisn to be verified. But it is unlikely, because the x-angle bump is reasonably well closed.  Even though the e - horizontal-angle bump spans only linear optical elements (apart from the solenoid), the observed tune variation suggests the presence of significant non-linear fields in that region of the HER.

W. KozaneckiMCC AP meeting, 29 July 04 Summary (more words...)  In the presence of parasitic crossings (sparsified by-2 pattern)  The peak specific luminosity is ~ 5% lower nominal PC separation) than in the by-4 pattern, where parasitic crossings should be negligible; the more positive the e - x-angle, the steeper the additional luminosity degradation.  The optimum e - x-angle is ~ 200  rad more negative (i.e.  weaker PC effects) in the by-2 pattern, than in the by-4 pattern. This suggests that in the presence of parasitic crossings, the optimum e - angle is a compromise between Xing-angle & PC-induced luminosity degradation.  The dependence of the PC-associated luminosity degradation on e - angle (i.e. on horizontal PC separation) is consistent with, and slightly weaker than, that predicted by beam-beam simulations.  “Pacman” bunches exhibit a luminosity degradation that varies from 20-25% (wrt to other minitrain bunches) near the optimum e- angle, to 10-15% at large positive angle (850  rad). This effect is not understood and requires further study.

W. KozaneckiMCC AP meeting, 29 July 04 Summary (in pictures)

W. KozaneckiMCC AP meeting, 29 July 04 Appendix: documentation & data sets  PEP-II e-log  collision data: dedicated MD, 1 Jul 04, day + swing + early owl shifts  HEB-only data: opportunistic MD, 14 Jul 04, swing shift  Data sets  collision data: PHYSICS4_DATA:[pep2.char.1Jul04]  L, currents, beam sizes, tunes, quads & bumps: lumtun_*_1Jul.dat  bunch-by-bunch data: XP*_BICDATA.MAT  gated camera: gacam_*_1Jul,dat  single-beam data: PHYSICS4_DATA:[pep2.ip.witold.smr04B]lumt_herxpcall_2_14Jul  orbit fit set to PR02 BPMS (HIPP) throughout