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Beam-beam sensitivity to parasitic crossings & Xing angle. Goal: measure the luminosity degradation associated with parasitic crossi ng s horizontal crossing angle Principle - PowerPoint PPT Presentation
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W. Kozanecki MCC AP meeting, 29 July 04
Goal:Goal: measure measure the luminosity the luminosity degradationdegradation associated with associated with parasitic crossings
horizontal crossing angle
PrinciplePrinciple
by-2 pattern: compare Lsp 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 Lsp 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 Beam-beam sensitivity to parasitic crossings & Xing angleto parasitic crossings & Xing angle
W. Kozanecki MCC AP meeting, 29 July 04
Experimental aspects (I)Experimental aspects (I)
Horizontal separation @ parasitic crossingsHorizontal separation @ parasitic crossings XP(e-) more +ve X(PC) nominal: X(PC) = 3.22 mm @ z = +/- 63 cm
for XPmax(e-) = - 0.60 / + 0.85 mrad, X 3.6 mm (+ 12%) / 2.7 mm (-17%)
+ x
W. Kozanecki MCC AP meeting, 29 July 04
Experimental aspects (II)Experimental aspects (II)
Quality/reproducibility of measurementsQuality/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 Lsp 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. Kozanecki MCC AP meeting, 29 July 04
I. Measure LI. Measure Lspsp degradation associated with degradation associated with
parasitic Xings + Xing angleparasitic Xings + Xing angle
Sparsified by-2 pattern,Sparsified by-2 pattern, LER/HER = 1.4/0.9 mA/b 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 -) (+- 0.3 mrad) to locate optimum e- angle (XPopt = 0 )
W. Kozanecki MCC AP meeting, 29 July 04
LLspsp degradation with parasitic Xings + Xing angle degradation with parasitic Xings + Xing angle (cont’d)
At XP = 0, + 850, - 600, - 300, + 300 rad Optimize LER+HER local & global skews, PR02 SEXT bumps
Optimize collision phase
Record tune spectra, gated camera data,
Lsp & Ib+,- patterns along the train
20% degradation at + 850 rad
Lsp vs. e- angle
3.0
3.2
3.4
3.6
3.8
4.0
4.2
-1000 -500 0 500 1000
XP [e-] (murad)
Lsp
(1E
30)
sp. by-2
After L sp optimization
at each XP setting
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. Kozanecki MCC AP meeting, 29 July 04
LLspsp degradation with parasitic Xings + Xing angle degradation with parasitic Xings + Xing angle (cont’d)
At XP = 0, +850, - 600, -300, + 300 rad Optimize LER+HER local & global skews, PR02 SEXT bumps
Optimize collision phase
Record tune spectra, gated camera data,
Lsp & Ib+,- patterns along the train
20% degradation at + 850 rad
Lsp vs. e- angle
3.0
3.2
3.4
3.6
3.8
4.0
4.2
-1000 -500 0 500 1000
XP [e-] (murad)
Lsp
(1E
30)
sp. by-2
After L sp optimization
at each XP setting
HER y spot size
0.27
0.28
0.29
0.30
0.31
0.32
-1000 -500 0 500 1000
XP[e-] (murad)
Ver
tica
l sp
ot
size
(m
m)
sp. by-2After L sp
optimization at each XP setting
+ 12%
HER x spot size
0.56
0.57
0.58
0.59
0.60
0.61
-1000 -500 0 500 1000
XP[e-] (murad)
Ho
rizo
nta
l sp
ot
size
(m
m)
sp. by-2After L sp
optimization at each XP setting
+ 6%
W. Kozanecki MCC AP meeting, 29 July 04
II. Measure LII. Measure Lspsp degradation associated with Xing angle only degradation associated with Xing angle only
by-4 patternby-4 pattern, same LER/HER bunch currents, 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. Kozanecki MCC AP meeting, 29 July 04
LLspsp degradation with Xing angle only 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 optimization @ + 850 rad,
L is higher at somewhat smaller
XP(e-), and then drops again.
y- displays a corresponding trend.
W. Kozanecki MCC AP meeting, 29 July 04
Even after optimization @ - 600 rad,
Lsp is higher at larger XP(e-).
y- displays a corresponding trend.
LLspsp degradation with Xing angle only degradation with Xing angle only (cont’d)
W. Kozanecki MCC AP meeting, 29 July 04
Similar effect seen in previousXing-angle MD (by-4 pattern, 11 May 04)
LLspsp degradation with Xing angle only degradation with Xing angle only (cont’d)
Specific luminosity
3
3.2
3.4
3.6
3.8
4
4.2
-1 -0.5 0 0.5 1
XP - XP opt (mrad)
L_
sp
(1
0^
30
mA
^-2
b^
-2)
1.35 / 0.85 mA/b, optzd @ XP=700
1.35 / 0.85 mA/b
RFTunes, skews,
sext. bumps
W. Kozanecki MCC AP meeting, 29 July 04
LLspsp degradation with Xing angle only 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
Lsp > 4.1 @ XP = “0”
7% degradation at + 850 rad
Lsp vs. e- angle
3.0
3.2
3.4
3.6
3.8
4.0
4.2
-1000 -500 0 500 1000
XP[e-] (murad)
Lsp
(1E
30)
by-4
After L sp optimization
at each XP setting
HER x spot size
0.55
0.56
0.57
0.58
0.59
0.60
0.61
0.62
-1000 -500 0 500 1000
XP[e-] (murad)
Ho
rizo
nta
l sp
ot
size
(m
m)
by-4
After L sp
optimization at each XP setting
+ 6%
HER y spot size
0.27
0.28
0.29
0.30
0.31
0.32
-1000 -500 0 500 1000
XP[e-] (murad)
Ver
tica
l sp
ot
size
(m
m)
by-4
After L sp
optimization at each XP setting
W. Kozanecki MCC AP meeting, 29 July 04
Without parasiticWithout parasitic Xings Xings (by-4) (by-4) LLspsp exhibits a exhibits a parabolicparabolic
dependence on dependence on XP(e-)XP(e-)
With parasiticWith parasitic Xings Xings (by-2)(by-2)
the peak Lsp is ~ 5% lower (@ nominal PC separation) than in the by-4 pattern
the larger XP(e-), the steeper the Lsp degradation
The optimum eThe optimum e-- x angle is ~ x angle is ~ 0.2 mrad 0.2 mrad more -ve in the by-2more -ve in the by-2 pattern (pattern ( weaker PCweaker PC effects) effects)
This suggests that in the This suggests that in the presence of parasitic Xings, presence of parasitic Xings, the the optimum eoptimum e-- angle angle is a is a compromisecompromise between between Xing-angleXing-angle & & PC-inducedPC-induced luminosity degradationluminosity degradation
LLspsp dependence on Xing angle & PC separation: dependence on Xing angle & PC separation: experimental summaryexperimental summary
Lsp vs. e- angle
3.0
3.2
3.4
3.6
3.8
4.0
4.2
-1000 -500 0 500 1000
XP[e-] (murad)
Lsp
(1E
30)
sp. by-2
by-4
After L sp optimization
at each XP setting
Normalized Lsp vs. e- angle
0.75
0.80
0.85
0.90
0.95
1.00
1.05
-1000 -500 0 500 1000
XP[e-] (murad)
Lsp
/ L
sp(X
P=
0)
by-4, msrd
by-4, fit
sp. by-2, msrd
sp. by-2, fit
W. Kozanecki MCC AP meeting, 29 July 04
LLspsp dependence on Xing angle & PC separation: dependence on Xing angle & PC separation: datadata vs. vs. simulationssimulations
Lsp vs. e- angle
3.0
3.2
3.4
3.6
3.8
4.0
4.2
-1000 -500 0 500 1000
XP[e-] (murad)
Lsp
(1E
30)
sp. by-2
by-4
After L sp optimization
at each XP setting
Normalized Lsp vs. e- angle
0.75
0.80
0.85
0.90
0.95
1.00
1.05
-1000 -500 0 500 1000
XP[e-] (murad)
Lsp
/ L
sp(X
P=
0)
by-4, msrd
by-4, fit
sp. by-2, msrd
sp. by-2, fit
Normalized Lsp vs. e- angle (by-4, no PC)
0.75
0.80
0.85
0.90
0.95
1.00
1.05
-1.2 -0.8 -0.4 0.0 0.4 0.8 1.2
Half crossing-angle (mrad)
Lsp
/ L
sp(X
P=
0)
SIm. (no PC)
by-4, msrd
by-4, fit
Lsp degradation vs. PC separation
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.5 2.0 2.5 3.0 3.5 4.0
Horizontal sepration at parastic crossing (mm)
Lu
min
osi
ty d
egra
dat
ion
fac
tor
msrd (1.43 / 0.89 mA/b)
sim. (1.56 / 0.96 mA/b)
Nominal PC separation
Simulation neglects Xing-angle effects
W. Kozanecki MCC AP meeting, 29 July 04
Related topics...Related topics...
ParasiticParasitic crossings crossings how do the Pacman bunches fare?
what is happening in the long minitrain?
Crossing angle (w/o PC)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. Kozanecki MCC AP meeting, 29 July 04
Parasitic crossings: how do the Pacman bunches fare?
Sparsified by-2 pattern
W. Kozanecki MCC AP meeting, 29 July 04
Parasitic crossings: the drooooping minitrain
W. Kozanecki MCC AP meeting, 29 July 04
e- x-angle response of Lsp & HER beam sizes in collision
Collisions, by-4
No optimization during scan
Collisions, by-4 Collisions, by-4
W. Kozanecki MCC 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 Collisions, by-4
W. Kozanecki MCC 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
Collisions, by-4
W. Kozanecki MCC AP meeting, 29 July 04
Summary (in words...)Summary (in words...)
In the by-4 pattern (where parasitic-crossing ing effects are In the by-4 pattern (where parasitic-crossing ing effects are expected to be negligible)expected to be negligible)
The specific luminosity exhibits a roughly parabolic dependence on the horizontal e- angle (after reoptimization @ 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 Lsp 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. Kozanecki MCC AP meeting, 29 July 04
Summary (more words...)Summary (more words...)
In the presence of parasitic crossings (sparsified by-2 pattern)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. Kozanecki MCC AP meeting, 29 July 04
Summary (in pictures)Summary (in pictures)
Lsp vs. e- angle
3.0
3.2
3.4
3.6
3.8
4.0
4.2
-1000 -500 0 500 1000
XP[e-] (murad)
Lsp
(1E
30)
sp. by-2
by-4
After L sp optimization
at each XP setting
Normalized Lsp vs. e- angle
0.75
0.80
0.85
0.90
0.95
1.00
1.05
-1000 -500 0 500 1000
XP[e-] (murad)
Lsp
/ L
sp(X
P=
0)
by-4, msrd
by-4, fit
sp. by-2, msrd
sp. by-2, fit
Normalized Lsp vs. e- angle (by-4, no PC)
0.75
0.80
0.85
0.90
0.95
1.00
1.05
-1.2 -0.8 -0.4 0.0 0.4 0.8 1.2
Half crossing-angle (mrad)
Lsp
/ L
sp(X
P=
0)
SIm. (no PC)
by-4, msrd
by-4, fit
Lsp degradation vs. PC separation
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.5 2.0 2.5 3.0 3.5 4.0
Horizontal sepration at parastic crossing (mm)
Lu
min
osi
ty d
egra
dat
ion
fac
tor
msrd (1.43 / 0.89 mA/b)
sim. (1.56 / 0.96 mA/b)
Nominal PC separation
W. Kozanecki MCC AP meeting, 29 July 04
Appendix: documentation & data setsAppendix: documentation & data sets
PEP-II e-logPEP-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 setsData 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 7052-8012 (HIPP) throughout