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Production of powerful coherent radiation in FEL based on two-dimensional distributed feedback

Production of powerful coherent radiation in FEL based on two-dimensional distributed feedback. Andrei Arzhannikov, Peter Kalinin, Stanislav Sinitsky, Budker Institute of Nuclear Physics, Russia, Novosibirsk. Naum Ginzburg , Nikolai Peskov, Alexander Sergeev, Vladislav Zaslavsky,

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Production of powerful coherent radiation in FEL based on two-dimensional distributed feedback

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  1. Production of powerful coherent radiation in FEL based on two-dimensional distributed feedback Andrei Arzhannikov, Peter Kalinin, Stanislav Sinitsky, Budker Institute of Nuclear Physics, Russia, Novosibirsk Naum Ginzburg, Nikolai Peskov, Alexander Sergeev, Vladislav Zaslavsky, Institute of Applied Physics RAS, Russia, Nizhny Novgorod Alan Phelps, Ivan Konoplev, Adrian Cross, SUPA, Department of Physics, University of Strathclyde, Glasgow Manfred Thumm.Forschungszentrum Karlsruhe, IHM, Germany

  2. A.V. Arzhannikov, Budker Institute of Nuclear Physics, Novosibirsk Transverse size is about 1.5m

  3. Using planar and coaxial 2D Bragg structures for synchronization of radiation in powerful FEM planar coaxial BINP, Novosibirsk U. of Strathclyde, Glasgow Fresnel parameter: Double-periodical corrugation of sidewalls: Ginzburg N.S., Peskov N.Yu., Sergeev A.S. // Opt.Comm.1993. V.96. N4–6. P.254; Opt.Comm.1994.V.112.P.151.

  4. Outline • 1. Planar FEM with 2D distributed feedback • a) Mode spectrum of planar 2D Bragg resonator • b) Cold microwave tests • c) Nonlinear dynamics of planar FEM with hybrid Braggresonator • d) Experimental studies of 75 GHz FEM at Budker Institute • 2. Coaxial FEM with 2D distributed feedback • a) Nonlinear dynamics of coaxial FEM with 2D Braggresonators • b) Experimental studies of 37 GHz FEM at Strathclyde University • 3. New schemes of oscillators with2D distributed feedback • a) Cherenkov masers • b) Advance to terahertz wave band • c) Optical lasers exploiting dielectric 2D Bragg structures

  5. 1. Planar FEM with 2D distributed feedback

  6. Coupled wave model of planar 2D Bragg resonator Cavity field: Diagram illustrating the scattering of the partial waves on the 2D Bragg grating:

  7. The coupled-wave equations (geometrical-optical approximation): Fresnel parameter : Diffraction is neglected

  8. Frequencies and Q-factors of the 2D Bragg resonator modes Modes located near the Bragg frequency: The analytical solution in the case: (1,0): II I I (1,1): (II) Mode located near the edge of the Bragg reflection band (1,1) : (I)

  9. Demonstration of high selectivity 2D Bragg resonator in 3D simulations(excitation of resonator by short microwave pulse) Short incidentmicrowave pulse 65 75 85 Incident pulse spectrum 3D electromagnetic code “CST Microwave Studio” • Symmetrical transverse distribution of the incident wave beam • Asymmetrical transverse distribution of the incident wave beam

  10. Asymmetrical incidentwave beam Symmetrical incident wave beam time (ns) time (ns) 0 0 10 10 18 18 Entire signal spectrum n=0 m=1 n=1 m=0 Final spectrum corresponds to excitation of fundamental mode at Bragg frequency 73.8 GHz 70 74 78 70 74 78 Fresnel parameter: 70 74 78 70 74 78 frequency (GHz) frequency (GHz) 3D simulation of fundamental mode excitation

  11. Partial waves structure of fundamental mode in geometrical-optical approximation and 3D simulations

  12. “Cold” tests of planar 2D Bragg structure 25 cm 25 cm 0.5 cm 2D sin corrugationdepth0.06 cmperioddz = dx = 0.5 cm(f ~ 60GHz) planar resonator (FZK)

  13. “Cold” tests of 2D Bragg structure measurement of transmission normal incidence inclined incidence l

  14. Results of “cold” measurements normal incidence of wave-beam f = 57.3 GHzQ = 600 f = 61.2 GHzQ = 500

  15. Results of “cold” measurements inclined incidence of wave-beam f = 59.75 GHzQ = 900

  16. Time–domain model of planar 2D Bragg FEM: x Amplification section z h h x h z h -gain parameter h h Sheet electron beam Diagram illustrating coupling of partial waves in 2D and 1D Bragg structures : 2D Bragg reflector Boundary conditions for 2D Bragg structure

  17. electron motion equations Boundary conditions: - phase of electrons to respect of synchronous wave - initial synchronism detuning -undulator period, Amplification section 1D Bragg reflector - RF electron current

  18. Simulation of nonlinear dynamics of planar FEM with hybrid Braggresonator 30 20 10 Time (ns) 0 0 40 80 120 160 200 Scaling: Spatial profile of partial waves in steady-state generation regime Establishment of steady-state generation regime Parameters of BINP FEM: L2D=18cm, L0=32cm, L1D=18cm, Lx=10cm, α2D= α1D =0.07cm-1, С=0.006

  19. Design of planar FEM with hybrid resonator consisting of upstream 2D Bragg mirror and downstream 1D Bragg mirrors. Beam width: 7 cm Scheme of 75 GHz planar FEM with hybrid resonator (BINP, Novosibirsk)

  20. Heterodyne diagnostic of radiation spectrum Frequency vs. electron synchronism detuning (nonlinear simulation) 76 Frequency (GHz) Частота (ГГц) 75 74 In experiments jumps between different longitudinal modes take place -2 -1.5 -1 -0.5 0 0.5 Experimental observation of single mode operation in planar 2D FEM (BINP) Arzhannikov et al. JETP. Lett. 2008.

  21. 1D Bragg reflector feedback loop Regular section Frequency (GHz) 2D Bragg reflector 76 Sheet electron beam 75 74 -1 -0.5 0 Stabilization of generation frequency in FEM with hybrid Bragg resonator by additional transverse feedback loop synchronism detuning

  22. 2. Coaxial FEM with 2D distributed feedback

  23. Coaxial FEM with hybrid resonator consisting of upstream 2D Bragg and downstream 1D Bragg mirrors 1 R 1 R 0.5 0.5 0 0 34 36 38 40 frequency (GHz) 2D Bragg mirror 1D Bragg mirror Reflection coefficient vs, frequency Azimuthal mode selection can be explained by the fact that overlapping of reflection zone takes place only for fundamental symmetric mode: m=0

  24. Zones of stationary generation regimes corresponding to excitation of modes with different number of azimuthal variation m Steady state generation with excitation nonsymmetrical mode m≠0 60 1000 50 800 40 1 3 2 600 30 Excitation fundamental symmetric mode m=0 20 400 10 200 0 -1.5 -1 -0.5 0 0.5 1 0 D (copper) Output power 95 % from radiation power Perimeter of high current beam100cm formed at High current institute ( Tomsk) Perimeter of Strathlylde FEM

  25. beam energy 0.5 MeV beam current 0.5 - 1 kA pulse duration 250 ns beam diameter 7 cm Experimental studies of co-axial 37 GHz FEM with 2D distributed feedback Department of Physics, University of Strathclyde Co-axial 2D Bragg structure I Konoplev et al. (TUPC86)

  26. Nonlinear modeling of longitudinal mode selection in 37 GHz FEM with hybrid Bragg resonator Parameters: L2D=10.4сm, L0=65сm, L1D=5.6сm, Lx=22сm, α2D=0.12сm-1 С≈4.6×10-3 efficiency 15 10 5 t 0 0 200 400 600 1 1 A+ 3 0.5 0.5 2 B+ A- 1 0 0 L 37 37 37.3 37.3 37.6 37.6 37.9 37.9 0 0 2 4 frequency (GHz) frequency (GHz)

  27. 37 GHz FEM Experiments with Hybrid Bragg Resonator 2D Bragg reflector 1D Bragg reflector 0 100 200 300 Radiation power 60 MW, efficiency ~6% Spectrum measurements by cut-off filters demonstrate azimuthal mode selection Heterodyne diagnostic of radiation spectrum demonstrate longitudinal mode selection Srf P (a.u.) 3 2 1 0 f (GHz)

  28. 3. New concepts

  29. abeam lz lx l2D a0 l0 - e l1D Slow-wave structure (b) Sheet electron beam 2D Bragg reflector 1D Bragg reflector Planar Smith- Purcell maser with 2D distributed feedback

  30. Towards terahertz wave band Traditional 1D Bragg reflector (coupling two counter propagating waves) 2D Bragg reflector Advanced 1D Bragg reflector (coupling propagating and cutoff modes) System extension over y-coordinate! Terahertz band FEL with advanced Bragg resonator (TUPC78)

  31. Optical lasers with 2D Bragg structure formed by dielectric film with chessboard corrugated surface active medium dielectric film

  32. Conclusion • 3D simulations and analytical models demonstrate high selectivity of planar and coaxial 2D Bragg structures for the large Fresnel parameters. Simulations correspond well to results of “cold” microwave tests and prove location of the most high-Q modes within forbidden band in the absence of lattice defects. • Modeling of nonlinear dynamics of planar and coaxial schemes of FEMs demonstrate possibility of using 2D distributed feedback for spatial synchronization radiation of sheet and hollow electron beams of width above 1000 wavelengths • Results of the theoretical analysis corroborated by modeling experiments carried out at Budker Institute (planar 75 GHz FEM) and Strathclyde University (coaxial 37 GHz FEM). • Combination of 2D and 1D Bragg structures provides large number of potentialities for manipulations of energy fluxes to expand interaction space in one or two transverse directions. • Concept of 2D distributed feedback can be applied to different types of radiation sources including lasers and solid-state devices.

  33. Formation of high-Q modes inside forbidden gap without defects of periodicity x Normal incidence z Inclined incidence Dependence reflection coefficient on incidence angle (degrees) 2D Bragg structures vs. photonic band gap (PBG) structures

  34. Eigenmode frequencies are located near • Eigenmode frequencies are located near I II Dispersion diagram for normal waves

  35. Microwave Pulse Mixed-envelope & Spectrum mV The trace of output RF pulse mixed with the signal from LO Undulator voltage 2.2kV(410-2T) Time (ns) The output RF pulse measured using crystal power detector • output spectrum from first 100 ns • output spectrum of last 100 ns • full spectrum Srf I~3.5kA V~500kV Frequency (GHz) Heterodyne diagnostic of radiation spectrum

  36. Spectrum of output signal from FEM based on 2D-1D two-mirror cavity Spectrum of the output signal from FEM based on 2D-2D two-mirror cavity Srf Srf f (GHz) f (GHz) Comparison of output RF pulses from FEM based on 2D-1D two mirror cavity and driven by the annular electron beams of currents: I  1.5 kA and I  3.5 kA I  1.5 kA I  3.5 kA Amplitude ar.un. In the case of high currents a faster rise time was observed however the total power as well as pulse duration were smaller Time(ns)

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