Coherent THz radiation source driven by prebunched electron
设计:李波 Coherent THz radiation source driven by pre-bunched electron beam H. Zhang, F. Bakkali Taheri, G. Doucas, I. V. Konoplev John Adams Institute, Department of Physics, Oxford University
Outline 设计:李波 Introduction Electron beam modulation Coherent THz radiation Summary and future work 11/5/2020 2
Introduction 设计:李波 Electromagnetic spectrum 30 um 11/5/2020 (10 THz - 0. 3 THz) 1 mm 3
Introduction 设计:李波 THz radiation sources Ø Solid-state electronic (Gun diodes, transistors, …) Ø Lasers (Gas, quantum cascade lasers, …) Ø Vacuum Electronic Terahertz Sources l Low power High power Compact sources with high mobility BWOs and their relatives, EIKs, TWTs (0. 1 -1. 0 THz and 103 -10 -3 W) l Compact gyrotrons with moderate mobility High magnetic field is required (0. 1 -1. 0 THz and 106 -10 -3 W ) l Stationary accelerator-based sources J. H. Booske et al, IEEE Trans. THz Sci. Technol. , 2011 11/5/2020 4
Introduction 设计:李波 THz radiation sources FEL Stationary accelerator-based sources FELs and beamline sources: CTR, CSR, CDR (0. 1 -10 THz and 10 -109 W) Free electron lasers (FEL) Coherent transition radiation sources (CTR) Coherent synchrotron radiation sources (CSR) Coherent diffraction radiation sources (CDR) CSR Advantage: tunability, high radiation power CDR 11/5/2020 5
Introduction 设计:李波 Coherent radiation enhancement For a bunch with Ne electrons: Incoherent radiation Coherence conditions: Coherent radiation Bunch length operating wavelength Bunch periodicity ≈ operating wavelength 11/5/2020 6
Electron beam modulation 设计:李波 Microbunch trains generation: plasma wakefield Self-modulation instability (SMI) W. Lu et al, PRL 2006 N. Kumar et al, PRL 2010 Electron beam modulation period equals to the plasma wavelength 11/5/2020 7
Electron beam modulation 设计:李波 Tunability of beam modulation Beam modulation after passing through a 5 cm capillary (by 3 D PIC code VSim) 0. 5 THz 1) 1. 0 THz 0. 5 THz 1. 5 mm 2) 1 THz 2. 0 THz 3) 1. 5 mm 2 THz 11/5/2020 1. 5 mm 8
Electron beam modulation 设计:李波 Beam modulation simulation • Beam parameters (based on ATF BNL) single particle energy - 50 Me. V; total bunch charge - 0. 5 n. C; bunch length - 1. 5 mm (5 ps); bunch transverse σr - 80 μm; bunch longitudinal profile - trapezoidal with equal rise and decay time (50 μm/0. 17 ps) 11/5/2020 9
Electron beam modulation 设计:李波 Bunch front 0. 5λp 1. 0λp Beam density distribution versus plasma density. (a) Initial beam distribution; (b)-(d) Beam density distribution after propagating 1. 8 cm in plasma with plasma density of 1. 24× 1016/cm 3, 2. 84× 1016/cm 3 and 11. 2× 1016/cm 3 respectively, the corresponding plasma wavelength is 300μm, 200μm and 100μm. 11/5/2020 10
Electron beam modulation λp=200 um 设计:李波 λp=100 um 0. 5λp The beam charge density on axis along the beam after different propagation distances 11/5/2020 11
THz coherent radiation 设计:李波 Smith-Purcell radiation Dispersion relation l : grating period (far-field region) n: harmonic order β: bunch velocity/c θ: observation angle 1/ x 0 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 11/5/2020 12
THz coherent radiation 设计:李波 Tunability of beam modulation SP signal spectrum from the beams with No modulation; 1 ps; 2 ps; 4 ps (500 m grating ) I(d. B) 11/5/2020 Frequency (GHz) 13
THz coherent radiation 设计:李波 THz Radiation from a micro-bunch train Bunch moving direction Electron bunch Grating Output pulse from the right port Current(A) Spectrum of the output pulse 9 micro-bunches were generated 11/5/2020 Peak at 1 THz Frequency(THz) 14
Conclusion 设计:李波 Ø A micro-bunch train can be generated when long picosecond electron beams propagate in plasma; Ø By changing the plasma density, the variation of microbunch train modulation frequency can be obtained; Ø Using such a pre-bunched beam, with well controlled periodicity, a tuneable coherent THz radiation can be generated and controlled by using periodic structures or dielectric material. 11/5/2020 15
Future work 设计:李波 Ø Analyse different THz radiation mechanisms Smith-Purcell radiation l Cherenkov radiation l Diffraction radiation l Ø Develop theory and simulation to Study of dispersion l Study of generation in case of finite ohmic and radiation losses in more details l Ø Design a novel periodic structure and build THz radiation source 11/5/2020 16
设计:李波 Acknowledgements This work was supported (in parts) by the: l UK Science and Technology Facilities Council (STFC) through grant ST/M 003590/1; l The Leverhulme Trust through the International Network Grant (IN-2015 -012).
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