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Donohue, J.T.

Paper Title Page
TUPP007 Simulation of a Smith-Purcell FEL Using a Particle-in-Cell Code
 
  • J.T. Donohue
    CENBG, Gradignan
  • J. Gardelle
    CESTA, Le Barp
  
 

A simulation of the generation of Smith-Purcell (S-P) radiation at microwave frequencies is performed using the two-dimensional particle-in-cell code MAGIC. The simulation supposes that a continuous, thin (but infinitely wide), mono-energetic electron beam passes over a diffraction grating, while a strong axial magnetic field constrains the electrons to essentially one-dimensional motion. We find that the passage of the beam excites an evanescent electromagnetic wave in the proximity of the grating, which in turn leads to bunching of the initially continuous electron beam. The frequency and wave number of the bunching are determined, and found to be close to those proposed by Brau and co-workers in recent work [1]. This frequency is below the threshold for S-P radiation. However, the bunching is sufficiently strong that higher harmonics are clearly visible in the beam current. These harmonic frequencies correspond to allowed S-P radiation, and we see strong emission of such radiation at the appropriate angles in our simulation, again in agreement with Brau's predictions. The bunching displays exponential growth both in time and space; the imaginary parts of the frequency and wave number are studied as functions of beam current.

[1] H. L. Andrews and C. A. Brau, Phys. Rev. ST Accel. Beams 7, 070701 (2004)

  
   
TUPP008 Simulation of Smith-Purcell Terahertz Radiation Using a Particle-in-Cell Code 262
 
  • J.T. Donohue
    CENBG, Gradignan
  • J. Gardelle
    CESTA, Le Barp
  
 

A simulation of the generation of Smith-Purcell (S-P) radiation at terahertz frequencies is performed using the two-dimensional particle-in-cell code MAGIC. The simulation supposes that a continuous, thin (but infinitely wide), mono-energetic electron beam passes over a diffraction grating, while a strong axial magnetic field constrains the electrons to essentially one-dimensional motion. We simulate two configurations, one similar to the Dartmouth S-P FEL [1], with a low energy continuous beam, and the other similar to the recent MIT experiment which uses a pre-bunched 15 MeV beam [2].

[1] A Bakhtyari, J. E. Walsh, and J. H. Brownell, Phys. Rev. Lett. E 65, 066503 (2002). [2] S. E. Korbly, A. S. Kesar, J. R. Sirigiri, and R. J. Temkin, Phys. Rev. Lett. 94, 054803 (2005)