Anomalous free electron laser interaction

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 483; no. 1; pp. 482 - 487
• Main Authors: Einat, M., Jerby, E., Kesar, A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2002
• Subjects: Free electron laser; Free electron laser; 41.60 Cr
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/S0168-9002(02)00366-2

Free electron lasers (FELs) are considered, typically, as fast wave devices. The normal FEL interaction satisfies the tuning condition ω≅( k z + k W) V z , where ω and k z are the em-wave angular frequency and longitudinal wave number, respectively, V z is the electron axial speed, and k W is the wiggler periodicity. This paper presents an anomalous FEL interaction, which may occur in slow-wave FELs (i.e. loaded by dielectric or periodic structures). The anomalous FEL effect presented here satisfies the tuning condition ω≅( k z − k W) V z , and it resembles the anomalous effect in slow-wave cyclotron resonance masers. A necessary condition for the anomalous interaction is ω/ k z < V z (i.e., the em-wave phase velocity should be slower than the electron beam). The paper presents a preliminary experimental result demonstrating the anomalous FEL effect in a stripline dielectric-loaded FEL experiment. A linear Pierce equation is applied to describe both the anomalous and normal FELs in the same framework. The paper is concluded with a conceptual discussion.