N.V.Agarin, A.V.Arzhannikov, V.B.Bobylev, A.V.Burdakov, N.S.Ginzburg*, E.V.Diankova**, V.G.Ivanenko, P.V.Kalinin, S.A.Kuznetsov, N.Yu.Peskov*, P.V.Petrov**, A.S.Sergeev*, S.L.Sinitsky, V.D.Stepanov
Budker Institute of Nuclear Physics, Novosibirsk, 630090, Russia;*Institute of Applied Physics, N.Novgorod, 603600, Russia; **RFNC-VNIITF, Snezhinsk, 456770, Russia
Millimetre wavelength planar FEL driven by sheet electron beam was studied in recent years in collaboration between BINP RAS and IAP RAS for achieving extremely high power at microsecond pulse duration. In a frame of this project two-dimensional distributed feedback has been proposed to provide spatial coherence of radiation from the large size sheet electron beam. The first operation of the FEL with novel feedback mechanism was reported at FEL'99. In this experiments a record energy of 100-J level was achieved in 4-mm 1-mcs pulses.
The present paper is devoted to progress in development of the novel scheme of FEL. It is shown that the 2-D Bragg resonator eigenmodes spectrum is depend on corrugation profile and several profiles were studied including ``chessboard grooves'' profile, which possess the mode spectrum similar to the ideal sin-corrugation. Absence of additional ``parasitic'' 1-D feedback circles, which took place on the corrugation used in previous experiments, allows narrowing radiation spectrum. The improved Bragg structures have been tested in ``cold'' measurements and corresponded well to simulations. The ``hot'' experiments are under progress currently. The goal of the present work is comparison of resonators of different geometry and the FEL efficiency enhancement.
