• N.S. Ginzburg, N.Yu. Peskov, A. Sergeev, V.Yu. Zaslavsky
  IAP/RAS, Nizhny Novgorod
• A.V. Arzhannikov, P.V. Kalinin, S.A. Kuznetsov, S.L. Sinitsky
  BINP SB RAS, Novosibirsk
• A.W. Cross, W. He, I.V. Konoplev, A. Phelps, C.W. Robertson, K. Ronald, C.G. Whyte
  USTRAT/SUPA, Glasgow
• V.B. Stepanov
  IHEP Protvino, Protvino, Moscow Region
• M. Thumm
  FZ Karlsruhe, Karlsruhe

For intense oversize relativistic electron beams with sheet and annular geometry the use of two-dimensional (2D) distributed feedback is beneficial for providing spatial coherence of the radiation and increasing the total radiation power [1]. Such feedback can be realized in planar and co-axial 2D Bragg resonators having double-periodic corrugations of the metallic side walls. High selectivity of such resonators has been demonstrated for large Fresnel parameters in the frame of coupled-wave model and in direct 3D simulations. Results of theoretical analysis are validated by data obtained in “cold” microwave measurements. Modeling of nonlinear dynamics of FEL with 2D distributed feedback also demonstrates advantages of novel feedback mechanism for production of spatial coherent radiation from large size electron beams. Simulation results are confirmed by recent experimental results where narrow frequency radiation was obtained at Ka-band co-axial and W-band planar 2D Bragg FELs which were realized at Strathclyde University [2] and Budker INP [3]. To advance 2D Bragg FEL in terahertz band the methods for extension of microwave systems over second transverse coordinate are discussed.

[1] N.S. Ginzburg, et al, Opt. Comm., 1993, v.96, p.254.
[2] I.V. Konoplev, et al, PRL, 2006, v.96, p.035002.
[3] A.V. Arzhannikov, et al, JETF Lett., 2008, v.87, p.715.

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