1 / 11

E-Cloud Effects in the Proposed CERN PS2 Synchrotron

This workshop at Cornell University presents the results of recent studies on e-cloud build-up and its effects on single-bunch instability in the proposed CERN PS2 synchrotron. The workshop discusses the motivations, outline, and parameters for e-cloud simulations, as well as the effects of e-cloud on beam stability. The conclusions suggest the need for mitigation measures to decrease the effective peak secondary to below 1.3.

rebekahs
Download Presentation

E-Cloud Effects in the Proposed CERN PS2 Synchrotron

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ECLOUD10 Workshshop, Oct. 8-12 Cornell University E-Cloud Effects in the Proposed CERN PS2 Synchrotron M. Venturini, M. Furman, and J-L Vay (LBNL) Work supported by the US DOE and LHC Acceleration Research Program (LARP)

  2. Motivations & Outline • One of the upgrade options considered for future LHC injector complex upgrades entails replacing PS with PS2. • Larger (1.34km circumference) • Higher energy (in@4GeV, extr@ 50GeV) • E-cloud identified as a possible factor limiting machine performance. • We present results of recent studies of • E-cloud build-up (POSINST) • Simulation of effect of e-cloud on single-bunch instability (WARP)

  3. Parameters for E-Cloud Build-up Simulations (POSINST)

  4. BUILD-UP IN FIELD-FREE REGION E-density vs. bunch population for various vacuum chamber sizes • Note roll-over of e-density with increasing bunch-population E-density vs. bunch population for various choices of max energy of yield curve BUILD-UP IN DIPOLE REGION

  5. E-density vs. peak secondary yield for various regions, train structures (extraction) E-density vs. peak secondary yield for various regions, train structures (injection)

  6. Summary of E-cloud Build-upStudies • Results obtained for 6D gaussian beams. Alternate bunch shape (parabolic transverse, flat longitudinal) yields build-up results 5-10% lower

  7. Effects of Ecloud on Beam • Focus on single-bunch e-cloud driven instability • Simulations carried out with WARP • Quasi-static approximation • Transversly uniform ecloud localized at finite no. of stations distributed along the ring (refreshed after each bunch passage) • Smooth approx. for lattice • 6D gaussian beam Selected parameters used in WARP simulations

  8. An fast head-tail like instability develops for sufficiently high e-cloud density • Detect instability by monitoring evolution of transverse emittances and amplitude of transverse centroid offset Vertical dipole moment a long the beam as the instability develops. Snapshots are taken for 5 successive bunch passage starting from turn no. 200 and 600 Evolution of vertical and horizontal emittances for three values of the e-cloud density

  9. Identify instability threshold by recording max. values of bunch emittances, & amplitude of centroid oscillations over 1000 turns (4.5ms). Start simulations with small initial transverse offset x0, y0. Bunch population: 5.9*1011. Negative chromaticities stabilize the motion (PS2 lattice has negative mom. compaction).

  10. To model electrons dynamics in dipoles use Warp option to pin electrons to vertical lines. • This suppresses instability in horizontal plane • Instability threshold in vertical plane somewhat higher (left Fig.) • Reducing bunch population is found to affect instability in vertical plane minimally while increasing stability in horizontal plane (middle Fig.) • At injection instability occurs at higher e-cloud densities (right Fig.)

  11. Conclusions • For vanishing chromaticities instability thresholds in terms of e-density are found to be about 0.4 in the vertical and 0.5 in the horizontal plane (units of 1012 m-3) • Chromaticities=-3 increase threshold by about 50% • Pinning electrons to vertical lines (dipoles) suppresses instability in the horizontal plane. Instability threshold in the vertical plane at re=0.8*1012m-3 • Above values lie in the mid-range of POSINST estimates of e-cloud build-up, suggesting that mitigation measures would have to be taken to decrease effective peak secondary to below 1.3

More Related