JACoW is a publisher in Geneva, Switzerland that publishes the proceedings of accelerator conferences held around the world by an international collaboration of editors.
TY - UNPB AU - Zen, H. ED - McIntosh, Peter ED - Burt, Graeme ED - Apsimon, Robert ED - Schaa, Volker R.W. TI - High Extraction Efficiency Operation of Oscillator-Type Free Electron Laser Driven by a Normal Conducting Linac J2 - Proc. of LINAC2022, Liverpool, UK, 28 August-02 September 2022 CY - Liverpool, UK T2 - International Linear Accelerator Conference T3 - 31 LA - english AB - The highest extraction efficiency (9.4%) of a Free Electron Laser (FEL) oscillator has been achieved at the mid-infrared FEL facility of Kyoto University*. The FEL is driven by a normal conducting linac consisting of a thermionic/photocathode RF gun and a traveling wave accelerator tube. The dynamic cavity desynchronization method**,*** was used to achieve the high extraction efficiency with a short macro-pulse duration (7 micro-s). Because of the interaction between the electron beam and FEL electromagnetic field, a maximum electron energy decrease of 16% was observed. An FEL micro-pulse energy of ~100 micro-J with the micro-pulse duration of 150 fs at the wavelength of 11 micro-m was observed. The detailed structure of the FEL micro-pulse was measured using a fringe resolved autocorrelation with a phase retrieval algorithm. As a result, superradiance ringing (or Burnham Chiao ringing), i.e. generation of multiple sub-pulses and 180-degree phase jumps between those sub-pulses, was experimentally observed for the first time in an FEL oscillator. PB - JACoW Publishing CP - Geneva, Switzerland ER -