Electron cloud studies at CESR Mark Palmer Cornell University Laboratory for Elementary-Particle Physics

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) Comparison measurements taken with 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 Oct 31, 2006 ILC DR Electron Cloud and Impedance/Instabilites

Measurement conditions at CESR Beam Energy Bunch Patterns Wiggler States Feedback Bunch Currents Low: 2 GeV 1t x 45b 6t x 5b 8t x 3b 12 on vs. 6 on 12 on on/off on 0.25 to 1.5 mA 1.0 to 3.0 mA 0.5 to 4.0 mA High: 5.3 GeV 9t x 6b all off at high energy all on 1.0 to 8.0 mA 1.0 to 5.0 mA Single beam (either e+ or e-) Pretzel off (separators off) 14 ns bunch spacing, 280 ns train spacing Oct 31, 2006 ILC DR Electron Cloud and Impedance/Instabilites

ILC DR Electron Cloud and Impedance/Instabilites Primary Diagnostics BSM (Beam Size Monitor) shuttered, 32 channel linear PMT array looking at synchrotron light BPM (Beam Position Monitor) uses four beam buttons, four channels per beam BSM and BPM use similar DAQ DAQ is based on a 72 MHz Digital Signal Processor (DSP) turn by turn and bunch by bunch data acquisition Oct 31, 2006 ILC DR Electron Cloud and Impedance/Instabilites

Turn-by-Turn Beam Profiles : Optics BSM synchrotron light optics line for positrons (optics line for electrons is similar) Off-axis Parabolic Mirror, diameter 4.5” , f=445mm Neutral Density Filters 32 CHANNEL PMT ARRAY TV CAMERA Gauss Filter 500 ± 40 nm Ground Glass Grid 0.3 0.1 0.01 Splitter T/R=50/50 Eyepiece, f=63mm Shutter Expander Lens f=-50 mm Beryllium Mirror in Beam Pipe CCD Hamamatsu linear PMT array (H7260K) followed by a 72 MHz Digital Signal Processor Quartz Vacuum Window Splitter T/R=50/50 Optics Box UV Filter Adjustable Mirror Adjustable Mirror Vertical Periscope Oct 31, 2006 ILC DR Electron Cloud and Impedance/Instabilites

Evidence of beam blow-up for e+ 2 GeV vertical beam size for 1x45 pattern, positrons 0.25 mA 0.35 mA 1 mA Notice advancing onset of beam size blow up as a function of bunch current Qualitative comparison of theory and measurement of instability onset (L.Schachter) Oct 31, 2006 ILC DR Electron Cloud and Impedance/Instabilites

Evidence of tune shift for positrons found 5.3 GeV vertical tune for 1x45 pattern, positrons (2 kHz Df ~ 0.005 DQ) 1.5 mA e+, 21 bunches (trailing bunches fell out) 0.5 mA e+, 45 bunches 2 kHz full scale Bunch # Bunch # 5.3 GeV vertical tune for 1x45 pattern, electrons 0.5 mA e-, 45 bunches 1.5 mA e-, 45 bunches e- tune change is much smaller than for e+ (but there is an effect) Bunch # Bunch # Oct 31, 2006 ILC DR Electron Cloud and Impedance/Instabilites

Transverse feedback, 2 GeV,1t x 45b positrons position and beam size FB on 0.75mA FB off 0.75 mA FB off 0.25 mA Vertical bunch by bunch feedback reduces the coherent motion of the beam and reduces the beam size at the end of the train electrons position and beam size FB off, 0.25 mA FB on 0.25 mA FB on 0.75 mA Oct 31, 2006 ILC DR Electron Cloud and Impedance/Instabilites

Spectra 2 GeV, e+, 1t x 45b, 0.8 mA/bunch bunch 1, BPM FFT data bunch 45, BPM FFT data horizontal spectrum horizontal spectrum vertical spectrum vertical spectrum Tune split coincides with beam blow-up, complicates tune extraction Oct 31, 2006 ILC DR Electron Cloud and Impedance/Instabilites

ILC DR Electron Cloud and Impedance/Instabilites Summary 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 6 of 12 wigglers turned off Other phenomena Electron beam size blow up and instability (ions?) – conditioning dependent Tune splitting, betratron sideband require explanation Vertical tune vs. bunch dependence for electrons Oct 31, 2006 ILC DR Electron Cloud and Impedance/Instabilites

ILC DR Electron Cloud and Impedance/Instabilites Plans Next Explore different bunch spacings in trains Employ witness bunch trailing trains Distinguish impedance, ion effects from ECE Detailed comparisons with simulation (SLAC/LBNL/FNAL collaboration) May 2007 Down Install RFAs (APS design) in North IR straight Solenoid wound pipe Longer term Start to prepare special wiggler vacuum chambers Electrodes and grooved Segmented RFAs SLAC/LBNL collaboration Installation April 2008 outside of ring Oct 31, 2006 ILC DR Electron Cloud and Impedance/Instabilites