Analyses of superradiance and spiking-mode lasing observed at JAERI-FEL

(WE-1-03) Presenting Author: Ryoichi Hajima

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

Japan Atomic Energy Research Institute

JAERI-FEL has achieved quasi-CW lasing with averaged power over 1kW, the initial goal of the R&D program. The FEL conversion efficiency obtained completely exceeds the well-known limit for non-bunched beam, which is determined by the number of undulator periods. We have conducted numerical studies for the characterization of lasing dynamics observed at JAERI-FEL.

Cavity-length detuning curves numerically calculated shows good agreement with experimental results. Lasing behavior exhibits transition from single supermode regime to spiking-mode regime, as the cavity-length detuning approaches to zero. Broadening of lasing spectrum observed in the experiments is clearly explained by these lasing dynamics. The conversion efficiency becomes maximum at perfect synchronization of the cavity length, where the lasing starts up with self-similar spikes of superradiance and reaches to chaotic regime. We also compare these results with analytical theory previously reported.