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Dyunin, E.

Paper Title Page
MOPP017 Velocity Shot-Noise Contribution and Collective Effects in SASE-FEL Radiation
 
  • A. Gover, E. Dyunin
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
  
 

The conventional analytical descriptions SASE-FEL do not take into account the electron velocity noise and collective effects. We use the general gain-dispersion relation for pre-bunched FEL in the linear regime [1] to define the FEL transfer function response to density and velocity modulation (initial condition problem) allowing for possible collective effect. This is used to derive expressions for SASE radiation line to velocity noise (random velocity modulation which exists even in the cold beam regime), in addition to the conventional shot noise (random density modulation). We find out for the realizable SASE FEL parameters [2] that the contribution of the velocity noise is not negligible relative to the shot noise. Also unexpectedly, collective effects may not be negligible in FELs even at short (UV) wavelength because the high beam current is being used.

[1] I.Schnitzer, A.Gover Nucl.Inst&Meth. Vol.A237. n.1-2, pp.124-140, 1985. [2]. R.Treusch, J.Feldhaus Eur. Phys. J. D, 26 pp.119-122, 2003

  
   
TUPP049 Smith-Purcell Distributed Feedback Laser 328
 
  • D. Kipnis, E. Dyunin, A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
  
 

Smith-Purcell radiation is the emission of electromagnetic radiation by an electron beam passing next to an optical grating. Recently measurement of relatively intense power of such radiation was observed in the THz-regime [1]. To explain the high intensity and the super-linear dependence on current beyond a threshold it was suggested that the radiating device operated in the high gain regime, amplifying spontaneous emission (ASE) [1,2]. We contest this interpretation and suggest an alternative mechanism. According to our interpretation the device operates as a distributed feedback (DFB) laser oscillator, in which a forward going surface wave, excited by the beam on the grating surface, is coupled to a backward going surface wave by a second order Bragg reflection process. This feedback process produces a saturated oscillator. We present theoretical analysis of the proposed process, which fits the reported experimental results, and enables better design of the radiation device, operating as a Smith-Purcell DFB laser.

[1] A.Bakhtyari, J.E.Walsh, J.H.Brownell, Phys.Rev. ·1065 006503 (2002). [2] H.L. Andrews, C.A. Brau, Phys.Rev. ST-AB 7, 070701 (2004).