High extraction efficiency observed at the JAERI free-electron laser

N. Nishimori, R. Hajima, R. Nagai, E. J. Minehara

Research output: Contribution to journalConference article

16 Citations (Scopus)


A high power Free-Electron Laser (FEL) has lased at a wavelength of 22 μm at the Japan Atomic Energy Research Institute (JAERI). The maximum power on a macro-pulse average is 1.7 kW, and it corresponds to an FEL energy of 160 μJ/micro-pulse. Extraction efficiency from the electron beam to the FEL radiation was measured to be 5.3% by an energy analyzer, when the maximum FEL power was coupled out. The rms wavelength spread was measured to be 4.6% at the same time. The extraction efficiency, in general, has a maximum value near the zero detuning length of an optical cavity, where (in contrast) the single-pass gain becomes smallest. A high peak current and a long macro-pulse duration are therefore indispensable for realizing high efficiency. The electron beam energy is 16.5 MeV, and the average current is 5.3 mA at a micro-pulse repetition rate of 10.4 MHz. The macro-pulse duration is 500 μs (5000 micro-pulses), long enough to reach saturation near the zero detuning length. The width and the peak current of the electron bunch are 5 ps FWHM and 100 A, respectively, at the undulator.

Original languageEnglish
Pages (from-to)266-269
Number of pages4
JournalNuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Issue number1-3
Publication statusPublished - 2001 Nov 21
Event22nd International Free Electron Laser Conference (FEL 2000) - Durham, NC, United States
Duration: 2000 Aug 132000 Aug 18


  • Free-electron laser
  • High power
  • Superconducting linac

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Instrumentation

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