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Broadband source of coherent THz radiation based on compact LINAC

Broadband source of coherent THz radiation based on compact LINAC . Ivan Konoplev , A. Seryi JAI, Department of Physics, University of Oxford J. Urakawa, A. Aryshev , K. Lekomtsev , M. Shevelev High Energy Accelerator Research Organisation, 1-1 Oho Tsukuba, Ibaraki 305-0801, Japan .

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Broadband source of coherent THz radiation based on compact LINAC

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  1. Broadband source of coherent THz radiation based on compact LINAC Ivan Konoplev, A. Seryi JAI, Department of Physics, University of Oxford J. Urakawa, A. Aryshev, K. Lekomtsev, M. Shevelev High Energy Accelerator Research Organisation, 1-1 Oho Tsukuba, Ibaraki 305-0801, Japan

  2. Introduction • Requirements to the radiation • Broadband (from 0.1THz to 10s of THz), short-pulse (fs), high-field intensity • Tuneable, single mode, single frequency • Amplification at THz frequencies • Average Power??? • Requirements to source • Compact • Energy efficient and easy to run • Capable of operating at high-repetition rate • Environment requirement • Not sensitive to surrounding environment • No or low level of ionising radiation • Low DC Voltage

  3. Available THz sources (solid state, not LINAC based) • Solid State Oscillators (High frequency Gunn, IMPATT and TUNNET diodes produce 100 mW@100GHz but falls as 1/f2 and at 400 GHz is typically in the range 0.1 to 1 mW) • Gas and Quantum Cascade Lasers (typically up 100 mW operating in range from 0.3THz to 5THz , • low temperature, large magnetic fields are required for QCLs • CO2 laser is required to pump the THz Gas laser • Laser Driven THz Emitters (operating in 0.2THz to 2THz with average power from nano- to microwatts)

  4. Available THz sources (vacuum tubes, not RF LINAC based) • Vacuum electronics: • Gyrotrons (not tuneable, high >10T magnetic fields is required) • BWO (in frequency range from 30GHz till 1.2THz, • power up to 100 mW@1.2THz) • Orotrons(Planar Smith-Purcell oscillators up to • 1THz, power from 100mW@1THz to 1W@0.3THz)

  5. Available LINAC based sources • Coherent Synchrotron radiation sources • Free Electron Lasers • Coherent Smith-Purcell radiation (cSPr) • Coherent Diffraction and Transition radiation

  6. 10MeV LINAC THz sources - proposal Schematic cartoon of the LINAC based radiation source with cavity and undulator/grating Bunching of continuous beam inside cavity 10MeV Coherence is insured by either installing a cavity or via pre-bunching electron beam making dimensions of the bunches smaller as compared with operating wavelength. Coherent radiation Incoherent radiation

  7. Price of the 40MeV LINAC facilities X-band RF gun To produce THz coherent synchrotron radiation (CSR)

  8. Smith-Purcell radiation observer x  Dispersion relation links radiated wavelength and observation angle  e-bunch y z x0 1/ x0 is the distance between beam and the periodic structure 2/ e is the electron beam - EM wave coupling parameter 3/ further electron beam is away smaller energy transfer to EM wave 10MeV beam should be 0.1mm away to generate radiation at 10THz For small  and  such that ()<<1/

  9. Smith-Purcell radiationE203 experiment at FACET SLAC 500um grating Exponential growth of intensity with decrease of beam grating separation Beam energy 20GeV Number of electrons per bunch 1.8E10 (up to 3nC) Signal intensity Toward the beam 600mm Position (AU) 450mm Green markers - 1.5 mm grating - approx. range (0.1THz -1THz) Blue markers – 0.25mm grating - approx. range (5THz- 0.7THz) Red markers - 0.05 mm grating - approx. range (3THz-17THz) Radiation and its spectral distribution Frequency (THz)

  10. Directionality of cSPr PiC modelling of cSPr radiation from 500um planar grating Ez x Ez is parallel to electron beam trajectory and located in x-z plane X   Ey y z grating Y Schematic position of the bunch moving toward us The divergence angle 2(approx. 6) of the cSPr from planar 1D grating of 500um period. Future gratings can be designed to minimise the divergence i.e. simplify the optics required to collect the signal. y1.4mm

  11. Recipes to improve lasing efficiency

  12. Surface fields excitation on 1D and 2D cylindrical PSL by electron-beam Surface fields excitation of by an electron beam. The plots were taken at 0.55ns (first column), and 0.45ns, 0.4ns (second column Bz, Ez plots respectively). SF scattered waves ve he Dashed lines squares indicate the location of PSLs, white line shows the boundary of the beam SF scattered waves ve he (a)

  13. Source of coherent SP radiation • Electron bunch having the following parameters: • 0.8nc • Bunch length 800fs • Electron energy 8MeV Er Er Ez FFT(Er) Ez

  14. Source of coherent SP radiationconcept of experiment at LUCX (KEK, Japan) The 2Q/ time (EM field decay time inside the cavity) is less as compared with distance between two neighbouring bunches Cylindrical 1/ The (2Q/) time is controlled by additional feedback mirrors 2/ Timing between feedback loop and distance between bunches also can be controlled 3/ Tuning via frequency selection inside feedback loop Cylindrical

  15. Conclusion • Brief overview of THz radiation sources • Steps toward coherent THz radiation source • Concept of new THz source of coherent radiation based on cSPr

  16. Thank you

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