Bunching phase evolution of short-pulse FEL oscillator system

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 445; no. 1; pp. 116 - 123
• Main Authors: Song, Su-Bin, June Hahn, Sang, Choi, Duk-In
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-05-2000
• Subjects: Bunching phase; Eikonal approximation; Electron detrapping; Bunching phase; Eikonal approximation; Electron detrapping; 41.60.Cr
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/S0168-9002(00)00125-X

We studied numerically the short-pulse FEL oscillator system using properly defined bunching phase
θ
B
and
Ψ
B
. In stable operation, we have found that the optical field “locks” the phase to π/2 at the trailing edge, which gives the maximum gain. Moreover, electrons can be detrapped from ponderomotive bucket due to the spatial variation of the optical field, and this detrapping effect is a major cause of the limit cycle oscillation of the system. The `bump’ of the output power during the amplification usually exists at the near-perfect cavity synchronism regime, which can be explained as the change of the matching condition between electron micropulse and optical pulse.