No. 63 (2014): Microbunching Instability

Issue Editors: I.S. Ko and J.-H. Han, Editor in Chief: W. Chou

The editor of this issue is Dr. In Soo Ko, a panel member and a senior scientist at PAL, Korea, and Dr. Jang-Hui Han, also from PAL. They collected 6 articles in the theme section “Microbunching Instability,” which were selected from a recent workshop at Pohang, Korea. These articles give a comprehensive review of this important beam dynamics topic in the study of high brightness electron beams.
The first article by A. H. Lumpkinoverviews experimental observations of microbunching instabilities. After discussing experimental results from LCLS, SCSS, SACLA, APS, and NLCTA, he claims that the instability detected through the generation of coherent optical transition radiation (COTR) occurs in various types of accelerators and electron guns. Some issues on the experimental side are summarized. S. Di Mitri reports the first experimental demonstration of control and suppression of microbunching instability by means of particles’ longitudinal phase mixing in a magnetic chicane. The article is extended to a discussion of applications of magnetic phase mixing to the generation of quasi-cold high-brightness ultra-relativistic electron beams. R. Warnock discusses the theory and evidence of coherent synchrotron radiation (CSR) in whispering gallery modes. Starting from Lord Rayleigh’s study on a whispering gallery phenomena at St. Paul’s Cathedral in London, he explains the theory and experimental observations in modern particle accelerators. J. Thangaraj reports coherent synchrotron radiation studies at the A0 emittance exchange (EEX) beamline of Fermi Lab. The measurements of CSR power as a function of bunch charge and length and the measurement of polarization of the CSR are shown. He then discusses a peak current increase with an energy-chirped beam. Finally, the latest developments in EEX configuration are described and two new configurations are proposed. The second article of A. H. Lumpkin shows mitigation plans for the microbunching instability related CORT at ASTA/FNAL. They plan to use the spectral differences between OTR and COTR, the scintillators in combination with bandpass filters, and temporal gating techniques to mitigate the diagnostics effects by a total factor of 100–1000. In the second contribution from S. Di Mitri, he shows how to cancel CSR kicks with optics balance. Cancellation of CSR kicks is extended to asymmetric optics. The theoretical model is first described in detail and then experimental results at FERMI@Elettra are compared with ELEGANT simulation.