IAP/RAS, Nizhny Novgorod
Kanazawa University, Kanazawa
Periodical Bragg structures may be considered as an effective way of controlling the electromagnetic energy fluxes and provision of spatially coherent radiation in the free electron lasers with oversized interaction space. A new scheme of terahertz band FEL with hybrid Bragg resonator consisting of advanced input Bragg mirror and traditional output Bragg mirror is proposed. Advanced Bragg mirror exploits coupling between two counter-propagating waves and the quasi cutoff wave and provides mode selection over the transverse index. Main amplification of the synchronous wave by the electron beam takes place in the regular section of the resonator. Small reflections from the output traditional Bragg mirror are sufficient for the oscillator self-excitation. Results of simulation of nonlinear dynamics of the FEL with a hybrid Bragg resonator is presented and demonstrate its operability in the terahertz frequency band with high (megawatt level) radiation power. In difference with the existing terahertz band FELs [1-2], the above scheme would be driven by a long pulse (microsecond) electron beam from Induction linear accelerators or Electrostatic accelerators.
[1] V.P. Bolotin, et al., Nucl. Instr. & Meth. Phys. Res. A, 2005, v.543, p.81.
[2] Y.U. Jeong, et al., Nucl. Instr. & Meth. Phys. Res. A, 2004, v.528, p.88.
IAP/RAS, Nizhny Novgorod
BINP SB RAS, Novosibirsk
USTRAT/SUPA, Glasgow
IHEP Protvino, Protvino, Moscow Region
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.
