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Electron-Cloud R&D

Past and Ongoing Activities

  1. Assessed electron-cloud effects at PEP-II as a function of beam intensity and fill pattern, and SEY. Concluded that a low-emission coating was required to ameliorate the effect.
  2. Simulated the APS (when operated with positrons) and the PSR, and compared with retarding field analyzer (RFA) measurements at those storage rings, thereby validating the code POSINST. For the PSR, this work contributed to the definitive conclusion that the observed high-intensity instability is caused by electrons.
  3. Assessed the electron-cloud effect in the SNS, vis-a-vis longitudinal pulse profile and intensity. Contributed to decision to TiN-coat the chamber of the ring.
  4. Assessed of the electron-cloud intensity at the LHC and SPS, and their proposed upgrade options, as a function of bunch spacing and intensity. Established a ranking of the risk of the various upgrade options on operational performance, with special attention to cryogenic load from the electron cloud.
  5. Modeling and detailed simulations of grooved-surface vacuum chambers, aimed at mitigating the electron-cloud. Specified grooved parameters (angle, pitch, depth) for most effective improvement. Currently planning tests of such grooved chambers at the SPS, in collaboration with CERN.
  1. Assessment of electron-cloud for the MI as a function of bunch current and fill pattern, including a higher RF frequency. From comparisons with recent RFA measurements, estimated that the peak SEY value is ~1.3-1.4. From this, we predicted the threshold in bunch intensity. Assessed effect of various fill patterns, including a pattern with an RF frequency of 212 MHz (as opposed to the current 53 MHz). Concluded that 212 MHz is much more favorable vis-a-vis the electron-cloud density than 53 MHz for a given total beam intensity.
  2. Simulation and measurement of a microwave signal through an electron cloud in the PEP-II positron ring. Measurements are in agreement with expectations, thereby demonstrating usefulness of the technique.
  3. Begun to assess electron-cloud effect for ILC DR and CESR-TA wigglers.
  4. Discovered, via simulations, a new type of resonance effect in magnetic fields. At our suggestion, these effects were experimentally looked for in an electron-cloud test chicane at PEP-II, and recently found as predicted. Currently exploring possible ramifications in realistic situations for other field configurations.
  5. Code development/support activities: invented a new, efficient, algorithm applicable to relativistic beams that speeds up fully self-consistent calculations by several orders of magnitude compared with existing algorithms. Developed a new leapfrog pusher, necessary for relativistic particles. Carried out code-to-code comparisons for the SPS in the context of a multi-institution benchmarking effort led by CERN. Validated 2D simulations obtained with POSINST with 3D simulations obtained with WARP, when using a non-dynamical beam model. Generally provided support with electron-cloud simulations at other institutions, especially those using the code POSINST.