1. Beamspot Longitudinal Profile Analysis Christopher O’Grady, Benoit Viaud March 17, 2006 Input from: Witold Kozanecki, Josh Thompson, Matt Weaver F.-J. Decker, Sasha Novokhatski, Dmitry Teytelman, Jerry Yocky

2. Goal Improve PEP Luminosity by studying beamspot. A lofty goal, but we succeeded once before: trickle injection counters. Maybe we’ve found something that could conceivably help … β y * … more later …

3. Topics Some reminders New-ish online measurements available Offline β y* measurements Bunch length modulation and phase transients: Theory vs. Experiment Bunch length measurements and difficulties.

4. Old Online Measurements: Every 10 Minutes in EPICS/History Buffers Sizes: x,y,z Centroids: x,y,z Tilts: x-z,y-z Several “boost” measurements provided by Matt. One problem: SVT alignment constants can create some bad answers online, esp. after downtime.

5. PEPII MAC Meeting, 14 Dec 04 A Reminder: Understanding July 2005 Minitrain Luminosity Loss

6. PEPII MAC Meeting, 14 Dec 04 Understanding the longitudinal luminosity distribution  The longitudinal luminosity distribution L(z) depends on depends on  the LER & HER bunch lengths  the relative position of the collision point Z c, the LER magnetic waist Z 0,LER, and the HER magnetic waist Z 0,HER  optical parameters (mainly  * y in LER & HER + weak dep. on  +,- y ) = f(z) [JT, AR] [COG, BV]

7. New Online Measurements: Online dL/dz Distribution 1 Run 1 Run Fit Results: Z c = 2.3+-0.1mm Σ z 2 =223+-5mm 2 β y * =12.4+-1.0mm Waist=1.2+-0.6mm Assumed equal for HER/LER Number of Events Z(mm)

8. New Online Measurements: β y * and Σ z Available each run in PEP history buffers. These points averaged over several days. βy*(mm) Σ z (mm) LER RF Change HER RF Change

9. New Online Measurements: Average Waist Position σ z (mm) mm Waist ZcZc An interesting occurrence on May 8, 2006, while having problems with “SK5”.

10. New Online Measurements: Phase Transient Abort Gap Phase transient plot available in real-time in “Odf Display” on a run-by-run basis. Uses very nice software written by Amedeo Perazzo. Average Z (mm)

11. Offline β y * Measurements Now 3 significantly different methods: Fitting dL/dz Measure σ y (z). “Boost” method: measures angular dispersion of the beam and correlations with spatial variables. Each method measures a function of β y * (HER) and β y * (LER) which we call β y * (effective). Need to know this function in order to compare more rigorously with PEP phase advance measurements.

12. β y * (effective) Formulae For “boost” method and dL/dz An approximate Taylor expansion (in D) for σ y (z) method Only extra assumption is that magnetic waists are at the same location

13. Offline β y * (eff) Measurements Maybe use RF phase scan as another measure of βy*? dL/dz Fit σ y (z) method (note different vert scale!) Boost method β y * (eff) from phase advance, 3 different emittance assumptions. Courtesy of Jerry Yocky.

14. Bunch Length Modulation and Phase Transients: Theory/Expt Predictions courtesy of Dmitry Teytelman and Sasha Novokhatski. Data from Apr 29 2005 thru May 12 2005. Σ z 2 (cm) Z avg (cm) Bucket Number Dmitry’s “raw” prediction Dmitry’s “raw” prediction scaled up by Sasha’s Bunch lengthening

15. Bunch Length Measurements (and Problems) An idea from WK in 2004: Assume σ z ~1/√V RF Measure Σ z at 2 different RF voltages by fitting dL/dz. 2 equations in 2 unknowns, solve for individual bunch lengths.

16. Bunch Length Measurements (and Problems) 0 10 20 RF Voltage (MV) Σ z (mm) Using Numbers from Sasha HER RF LER RF Why is Σ z changing when RF doesn’t change?

17. Fits (Likelihood) Chisq: 108, for 100-5 d.o.f. Prob: 17% Norm 1.02125e+00 1.47665e-03 Zc 3.68052e-02 2.66972e-03 CapSigzSqrd 2.45044e+00 1.03738e-02 BetaY 1.33328e+00 1.96984e-02 Waist -8.00839e-02 1.26765e-02 Chisq: 132, for 100-5 d.o.f. Prob: 0.7% Norm 1.02514e+00 1.63293e-03 Zc 2.64888e-02 2.62672e-03 CapSigzSqrd 2.21443e+00 9.75603e-03 BetaY 1.18414e+00 1.71040e-02 Waist -4.35208e-02 1.11199e-02 Run 62101-62613 Run 62762-63049

18. Bunch Lengths RF Changes RF ChangeHER Bunch Lengths (mm) (Sasha value) LER Bunch Lengths (mm) (Sasha value) Feb. 6 LER 4.05->4.5MV 12.0+-1.0 @13.4MV (12.0)10.8+-1.1 @4.05MV (11.2) 10.2+-1.0 @4.5MV (10.3) Mar. 2 HER 13.4->15.4MV 13.5+-0.4 @13.4MV (12.1) 12.6+-0.4 @15.4MV (11.4) 8.0+-0.7 @4.5MV (10.3)

19. Possible Solutions Detector/Analysis Effect Theta, phi dependencies (“holes”) Momentum Bsz subtraction Accelerator Effect Tilts, Xing angles (have taken out 21mrad tilt: it didn’t seem to matter, so maybe small xing angle doesn’t matter too) Bucket dependence (phase transient) Beam Currents Changing with Time HER/LER waists not equal Non-gaussian bunches Coupling Sqrt(V RF ) law not correct Accelerator wakefields changing with time

20. To Do Understand β y* measurement Understand bunch length measurement Fix annoying calibration constants problem that messes up online data sometimes.

21. Backup Slides

22. PEPII MAC Meeting, 14 Dec 04 Precision of Online Measurements Parameter RMS Width Precision (10 minutes) x 80  m 0.9  m y 40  m 0.5  m z 7000  m 90  m dx/dz (20mrad) -0.25mrad Resolution dominated

23. Detector Effects: “The Hole”

24. Ratios: Fit/Data

25. BetaY* Measurements

26. Comparing dL/dz and σ y (z) Results for β y * (eff) Different Formula for β y * (eff) for dL/dz and σy(z). Can we extract some interesting information from the discrepancy? βy*(HER) [cm] βy*(LER) [cm] Looks unlikely that those are the values for βy*(HER) and βy*(LER).

27. Time dependence

28. Use Both RF and HER/LER Current Dependence LER current dep: 1 mm/mA/bunch @4.5MV. 1700mA->1550mA. HER current dep 1.25 mm/mA/bunch @15.4MV. 1050->1200 mA. 1700 bunches. Bunch lengths 7.1/13.9mm before RF change.

29. Fit Keeping β y * constant Norm1 1.02460e+00 1.37052e-03 Zc1 3.67971e-02 2.63027e-03 CapSigzSqrd1 2.48485e+00 8.22162e-03 Waist1 -7.26644e-02 1.14042e-02 Norm2 1.02070e+00 1.41577e-03 Zc2 2.64300e-02 2.67340e-03 CapSigzSqrd2 2.17424e+00 6.99837e-03 Waist2 -4.94528e-02 1.25768e-02 BetaY 1.26674e+00 1.31597e-02 Norm 1.02125e+00 1.47665e-03 Zc 3.68052e-02 2.66972e-03 CapSigzSqrd 2.45044e+00 1.03738e-02 BetaY 1.33328e+00 1.96984e-02 Waist -8.00839e-02 1.26765e-02 Norm 1.02514e+00 1.63293e-03 Zc 2.64888e-02 2.62672e-03 CapSigzSqrd 2.21443e+00 9.75603e-03 BetaY 1.18414e+00 1.71040e-02 Waist -4.35208e-02 1.11199e-02 Chisq: 270, for 200-9 d.o.f. Prob: 0.01%

30. Is Simultaneous Fit the Right Thing To Do? βy* looks like it’s changing, so I don’t think so. Suggested by chi**2 too. Maybe need to take weighted average of run-by-run fits.

31. Sasha Bunch Lengths LER current dep: 1-2 mm/mA/bunch HER current dep: 1.25mm/mA/bunch

32. Test Cuts Test CutCapSigzSqrd (pre-RF change)CapSigzSqrd (post-RF change) 45<phi<132 or 225<phi<315 Other phi regions 2.46+-.02 2.45+-.01 2.25+-.02 2.20+-.01 Cos(theta1)<0.75 Other cos regions 2.47+-.02 2.44+-.01 2.23+-.01 2.20+-.01 400<odfbunch<500 Other bunches 2.47+-.03 2.44+-.01 2.18+-.03 2.20+-.01

33. Why is CapSigmaZ Changing? PeriodΣ z 2 (cm) (chisq prob) Feb 7 -> Mar 12.45 (4%) Feb 7 -> Feb 162.50 (44%) Feb 16-> Mar 12.41 (29%)

34. Fit Chisq vs. Time

35. “Average” Waist Location

36. An Interesting Period : May 7, 2006 Integrating venturini: 2.5mm waist offset -> 1% lumi drop. In Toy MC move both waists by 2.5mm -> σ z 6.95->6.97 In Toy MC move one waist by 5.0mm -> σ z 6.95->7.00 Online we are fitting z distribution with no x-z rotation removed..

37. Currents on May 7

38. Other Quantities

39. Cause of Z-size Increase?

40. Try Fitting Waists Separately FCN=190.556 FROM MIGRAD STATUS=CONVERGED 583 CALLS 584 TOTAL EDM=2.9329e-07 STRATEGY= 1 ERROR MATRIX UNCERTAINTY 2.1 per cent EXT PARAMETER STEP FIRST NO. NAME VALUE ERROR SIZE DERIVATIVE 1 Norm 1.01745e+00 3.15268e-03 -6.02141e-06 -5.37855e-02 2 Zc 3.43245e+00 5.95731e-02 1.21247e-04 3.31760e-02 3 CapSigzSqrd 2.29166e+02 2.19053e+00 -4.92098e-05 1.23174e-02 4 BetaY 1.35077e+01 4.63520e-01 1.04731e-04 -3.71524e-03 5 Waist1 4.74866e-01 3.31536e-01 -6.27979e-04 2.95167e-03 6 Waist2 1.49115e+00 3.32570e-01 -6.32963e-04 2.51453e-03 chi2: 190.556 FCN=190.554 FROM MIGRAD STATUS=CONVERGED 457 CALLS 458 TOTAL EDM=1.31813e-05 STRATEGY= 1 ERROR MATRIX ACCURATE EXT PARAMETER STEP FIRST NO. NAME VALUE ERROR SIZE DERIVATIVE 1 Norm 1.01745e+00 3.21050e-03 4.16884e-05 1.99746e-01 2 Zc 3.43246e+00 5.97447e-02 3.37961e-04 -1.58795e-01 3 CapSigzSqrd 2.29167e+02 2.19654e+00 8.50484e-05 2.00990e-01 4 BetaY 1.35170e+01 4.65736e-01 2.05758e-04 -8.71181e-02 5 Waist 9.42344e-01 3.25642e-01 1.69247e-03 -4.44502e-02 chi2: 190.554

41. Logbook Entries for May 7 From operators logbook before change in σ z : “PEM was replaced SK5 power supply; it will not trim up after that, they are still trobleshooting the PS controller at the end of the shift” at 1000x1400mA ran into HER Tune problems again. Specific was in the yellow at 2.4. Grabbed SK5L, SK2, SK2L and SK3L and got Speific back into the green around 3.2. This fixed the HER tunes problems so far... After change in σ z : 1 Accessed to PEP zone 4 to to increase water flow to SK5 magnet: Found lower 2 coil had little or no flow. Connected water flow in parallel instead of series thru lower 2 coils. Flow thru those coil improved four fold after backflush.2 T474 experiments ended after 2hours into the shift.3 2-8,13-1 Thyratrons were replaced and other SML items were addressed