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Recent electron cloud studies at CESR David Rice Cornell University Laboratory for Elementary-Particle Physics.

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Presentation on theme: "Recent electron cloud studies at CESR David Rice Cornell University Laboratory for Elementary-Particle Physics."— Presentation transcript:

1 Recent electron cloud studies at CESR David Rice Cornell University Laboratory for Elementary-Particle Physics

2 Recent electron cloud studies at CESR David Rice Cornell University Laboratory for Elementary-Particle Physics A special thanks to Eugene Tanke and Jerry Codner for preparation of these slides.

3 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 3 Presentation Outline Measurements Performed at CESR Key Beam Diagnostics used Electron Cloud Experiments Other Phenomena

4 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 4 Measurements made at CESR Investigation of possible electron cloud effects –Look for vertical tune shift for positrons (coherent) –Look for positron beam size blow up (incoherent) –Check effects for electrons Other phenomena –Onset of instability in vertical beam size and vertical position –Tune split (betatron sideband) vertical and horizontal –Other effects on positrons and electrons

5 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 5 Machine conditions at CESR Machine conditions –electrostatic separators always off –bunch patterns one long train of 45 bunches, 14 ns spacing widely separated (280 ns) trains of 5 bunches (14 ns spacing) used in operation –bunch currents 0.25 to 1.5 mA per bunch in 45 bunch trains, 14 ns spacing 1.0 to 8.0 mA per bunch in widely separated bunch trains –beam energy: high (5.3 GeV) and low (~ 2 GeV) –12 wigglers on versus 6 wigglers on (low energy only) –Transverse feedback on and off –With and without low field solenoid in 15 meter straight section

6 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 6 Next topic Measurements Performed at CESR Key Beam Diagnostics used Electron Cloud Experiments Other Phenomena

7 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 7 Key beam diagnostics used (1) BSM (Beam Size Monitor) –shuttered, 32 channel linear PMT array looking at synchrotron light –one sample per channel per bunch on each turn –separate DAQ for each species samples up to 183 bunches –optics accommodate linear CCD array and TV camera BPM (Beam Position Monitor) –uses four beam buttons, four channels per beam –one sample per channel per bunch per species on each turn –one DAQ samples up to 183 bunches per species Major Differences –BPM is 2 beams per DAQ, 8 channels total (8k turns for 45 bunches) –BSM is 1 beam per DAQ, 32 channels –BSM requires much more data to be transferred –BSM requires much more sophisticated and CPU intensive analysis

8 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 8 Key beam diagnostics used (2) : Optics BSM synchrotron light optics line for positrons (optics line for electrons is similar) Adjustable Mirror Beryllium Mirror in Beam Pipe Quartz Vacuum Window UV Filter Adjustable Mirror Vertical Periscope Off-axis Parabolic Mirror, diameter 4.5”, f=445mm Eyepiece, f=63mm CCD 0.01 0.1 0.3 Neutral Density Filters TV CAMERA Ground Glass Grid 32 CHANNEL PMT ARRAY Expander Lens f=-50 mm Shutter Gauss Filter 500 ± 40 nm Splitter T/R=50/50 Optics Box Splitter T/R=50/50 Hamamatsu linear PMT array (H7260K) followed by a 72 MHz Digital Signal Processor

9 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 9 Key beam diagnostics used (1) BSM (Beam Size Monitor) –shuttered, 32 channel linear PMT array looking at synchrotron light –one sample per channel per bunch on each turn –separate DAQ for each species samples up to 183 bunches –optics accommodate linear CCD array and TV camera BPM (Beam Position Monitor) –uses four beam buttons, four channels per beam –one sample per channel per bunch per species on each turn –one DAQ samples up to 183 bunches per species Major Differences –BPM is 2 beams per DAQ, 8 channels total (8k turns for 45 bunches) –BSM is 1 beam per DAQ, 32 channels –BSM requires much more data to be transferred –BSM requires much more sophisticated and CPU intensive analysis

10 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 10 Key beam diagnostics used (3): DAQ DAQ is based on a 72 MHz Digital Signal Processor (DSP) capable of turn by turn and bunch by bunch data acquisition Similar architecture for BPM and BSM

11 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 11 Beam Diagnostics Time Line Beam diagnostics used in EC experiments evolved during 2006. Initial diagnostics were turn-by-turn beam position measurements for each bunch and measurements of vertical beam size averaged over all bunches. Turn-by-turn vertical beam size measurements for each bunch were added for electrons in June and for positrons in August.

12 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 12 Next topic Measurements Performed at CESR Key Beam Diagnostics used Electron Cloud Experiments Other Phenomena

13 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 13 Evidence of e+ beam size blow up found 0.5 mA 0.75 mA 1 mA 2 GeV vertical beam size for 1x45 pattern, positrons Notice advancing onset of beam size blow up as a function of bunch current 0.25 mA 0.35 mA

14 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 14 Theory and measurement of instability onset 0.35 mA Details were presented in Levi Schachter’s talk Qualitative comparison: if the transverse eigen-frequency becomes comparable with the corresponding betatron frequency ( x c), then the transverse motion becomes unstable. Need to take into account the horizontal motion as well.

15 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 15 Evidence of tune shift for positrons found 5.3 GeV vertical tune for 1x45 pattern, positrons 5.3 GeV vertical tune for 1x45 pattern, electrons 0.5 mA e+, 45 bunches 0.5 mA e-, 45 bunches 1.5 mA e+, 21 bunches (trailing bunches fell out) 1.5 mA e-, 45 bunches 2 kHz full scale Bunch # e- tune change is much smaller than for e+ (but there is an effect) (2 kHz  f ~ 0.005  Q)

16 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 16 Predictions of e- density (J. Crittenden, 3/9/2006) Electron densities modeled with ECLOUD and compared with measured tune shift in 45 bunch e+ train Assume simple tune shift model (Ohmi et al., APAC2001, p.445-447): Calculate e- densities in drifts (19%), bends (62%) and quads (9%) at 5.3 GeV. Average density of 4E11/m 3 produces 1 kHz (0.0025) tune shift with =30 m

17 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 17 Observations with 6t x 5b pattern, e+ 1 kHz vertical tune vs. bunch, I = 1 mA Bunch # (trains start at bunches 6,11,16, 21 and 26) Bunch # Vertical position Vertical beam size (mm) 5.3 GeV vertical tune for 6 trains x 5 bunch pattern, positrons Positive tune shift from first to fifth bunch in a train is 0.4 kHz See difference from first train to trailing trains of 0.1 kHz Beam size has bunch dependence Vertical beam position (mm)

18 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 18 Observations with 6t x 5b pattern, e- 5.3 GeV vertical tune for 6 trains x 5 bunch pattern electrons, 8 mA per bunch There is an effect on electrons similar to the electron cloud for positrons, but it is: 1. weaker (1 kHz for 8 mA) 2. vertically defocusing

19 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 19 Impact of wigglers on electron cloud effects, e+ Started with all 12 wigglers on and subsequently ramped down 6 wigglers with stored beam Notice no significant change in vertical tune vs. bunch (adjacent plot); E cloud in CESR is not dominated by the wigglers A rough estimate of photon flux from wigglers, using ECLOUD, predicts average electron densities of 3E12 for ~12 m by each of 2 wiggler clusters. We might expect 0.25 kHz change in tune shift from first to last bunch.

20 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 20 Next topic Measurements Performed at CESR Key Beam Diagnostics used Electron Cloud Experiments Other Phenomena

21 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 21 Impact of vacuum processing August 2006July 2006 Vertical Beam Size (mm) Impact of vacuum processing after a leak repair in June 2006 Electrons Onset of beam size growth as evidenced by averaged data Single Turn Onset of beam size growth as evidenced by averaged data

22 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 22 Compare 12 vs. 6 wigglers on, e+ Single Turn Distribution (dots) and Gaussian fit (red line) Started with all 12 wigglers on and subsequently ramped down 6 wigglers with stored beam, compensating for the 0.1 vertical tune shift per wiggler with local quadrupole changes. 2 GeV positrons, 0.5 mA/bunch for 1x45 Pattern PMT channel number Vertical Beam Size for 100 turn averaged data (left) and single turn data (right) Intensity (a.u.)

23 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 23 Compare 12 vs. 6 wigglers on, e- 100-turn averaged beam sizes (left) as compared to single turn beam sizes blown up by centroid motion (see movie at left bottom) 24-Aug-2006 data 2 GeV electrons, at 3 bunch currents 1x45 Pattern Distribution on PMT for bunch 30, bunch current 0.5 mA PMT channel number Intensity (a.u.)  Qy ~ 2kHz w/ 12 wigglers I = 0.8 and 0.9 mA/bunch  Qy ~ 0.6 kHz w/ 6 wigglers I = 0.6 mA/bunch (could be due to current difference)

24 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 24 Transverse feedback, 12 wigglers, e+  Qy ~ 4kHz @ I = 0.86mA/bunch Vertical bunch by bunch feedback reduces the coherent motion of the beam and reduces the beam size at the end of the train 2 GeV tunes, position and beam size for 1x45 pattern, positrons Multiple peaks and poor SNR for file 423 & 425

25 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 25 Vertical bunch by bunch feedback reduces the coherent motion of the beam and reduces the beam size at the end of the train Transverse feedback. 12 wigglers, e-  Qy ~ 0.25 kHz @ I = ~0.7 mA/bunch 2 GeV tunes, position and beam size for 1x45 pattern, electrons Multiple peaks and poor SNR for file 438

26 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 26 Tune split: 2 GeV, e+ example, 1t x 45b bunch 1, BPM FFT databunch 45, BPM FFT data 0.8 mA per bunch 0.3 mA per bunch horizontal spectra all bunches, spectrum analyzer vertical spectra horizontal spectra vertical spectra

27 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 27 Summary & Conclusions Effects seen: Electron cloud –See clear evidence in tune versus bunch for positrons vs. electrons –See clear evidence in beam size versus bunch No effects seen: 12 vs. 6 wigglers, solenoids –6 of 12 wigglers turned off, 3 in each straight section, W & E –Low current solenoid in straight section, < 2% of storage ring Other phenomena –Electron beam size blow up and instability (ions?) –Tune split, betratron sideband require explanation (KEK help) –Vertical tune vs. bunch dependence for electrons Next –Explore different bunch spacings –Distinguish impedance, ion effects from ECE –Compare with calculations

28 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 28 Acknowledgements M. Billing, G. Codner, J. Crittenden, M. Forster, M. Palmer, D. Rice, E. Tanke (Cornell) L. Schachter, Cornell visitor (Technion) R. Holtzapple, and J. Kern (Alfred University) B. Cerio (Colgate University) M. Watkins (CMU)

29 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 29 Bunch 1, e+ at 0.25 mA e+ Bunch 1 I=0.25m A/bunch 12 Wigglers On File 570 e+ Bunch 1 I=0.25mA/b unch 12 Wigglers On File 570

30 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 30 Bunch 3, e+ at 0.25 mA e+ Bunch 3 I=0.25mA/bu nch 12 Wigglers On File 570

31 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 31 Bunch 4, e+ at 0.25 mA e+ Bunch 4 I=0.25mA/b unch 12 Wigglers On File 570

32 Sept 27, 2006 ILC Damping Rings R&D Workshop at Cornell 32 Bunch 20, e+ at 0.25 mA e+ Bunch 20 I=0.25mA/bu nch 12 Wigglers On File 570

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