Author: Yang, X.
Paper Title Page
THP107 Source of Microbunching at BNL NSLS Source Development Laboratory 2324
 
  • S. Seletskiy, Y. Hidaka, J.B. Murphy, B. Podobedov, H.J. Qian, Y. Shen, X.J. Wang, X. Yang
    BNL, Upton, Long Island, New York, USA
 
  We report experimental studies of the origins of electron beam microbunching instability at BNL Source Development Laboratory (SDL). We eliminated laser-induced microbunching by utilizing an ultra-short photocathode laser. The measurements of the resulting electron beam led us to conclude that, at SDL, microbunching arising from shot noise is not amplified to any significant level. Our results demonstrated that the only source of microbunching instability at SDL is the longitudinal modulation of the photocathode laser pulse. Our work shows that assuring a longitudinally smoothed photocathode laser pulse allows mitigating microbunching instability at a typical FEL injector with a moderate microbunching gain.  
 
THP134 Lifetime Measurement with Pseudo Moveable Septum in NSLS X-ray Ring 2375
 
  • G.M. Wang, J. Choi, R. Heese, S.L. Kramer, T.V. Shaftan, X. Yang
    BNL, Upton, Long Island, New York, USA
 
  Funding: Work supported by U.S. DOE, Contract No.DE-AC02-98CH10886
The National Synchrotron Light Source II (NSLS-II) is a state of the art 3 GeV third generation light source currently under construction at Brookhaven National Laboratory and starts to commission in 2014. The beam injection works with two septa and four fast kicker magnets in an injection section. To improve the injection stability and reproducibility, we plan to implement a slow local bump on top of the fast bump so that the fast kicker strength is reduced. This bump works as a pseudo movable septum. We can also use this ‘movable’ septum to measure the storage ring beam partial lifetime resulting from the septum edge and possibly increasing the lifetime by moving the stored beam orbit away from the edge. We demonstrate the feasibility of this idea, by implementing DC bump in NSLS X-ray ring. We report the results of beam lifetime measurements as a function of the amplitude of this bumped orbit relative to the septum and the idea of a slow bump that could reduce the fast bump magnet strengths.
 
 
THP148 Experimental Investigation of Superradiance in a Tapered Free-Electron Laser Amplifier 2396
 
  • Y. Hidaka, J.B. Murphy, B. Podobedov, S. Seletskiy, Y. Shen, X.J. Wang, X. Yang
    BNL, Upton, Long Island, New York, USA
 
  We report experimental studies of the effect of undulator tapering on superradiance in a single-pass high- gain free-electron laser (FEL) amplifier. The experiments were performed at the Source Development Laboratory (SDL) of National Synchrotron Light Source (NSLS). Efficiency was nearly tripled with tapering. Both the temporal and spectral properties of the superradiant FEL along the uniform and tapered undulator were experimentally characterized using frequency-resolved optical gating (FROG) images. Numerical studies predicted pulse broadening and spectral cleaning by undulator tapering Pulse broadening was experimentally verified. However, spectral cleanliness degraded with tapering.
* T. Watanabe et al, Phys. Rev. Lett. 98, 034802 (2007).
** X.J. Wang et al, Phys. Rev. Lett. 103, 154801 (2009).