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Register a new userMeasurements of Terahertz Radiation Generated using a Metallic, Corrugated Pipe
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A method for producing narrow-band THz radiation proposes passing an ultra-relativistic beam through a metallic pipe with small periodic corrugations. We present results of a measurement of such an arrangement at Brookhavens Accelerator Test Facility (ATF). Our pipe was copper and was 5 cm long; the aperture was cylindrically symmetric, with a 1 mm (radius) bore and a corrugation depth (peak-to-peak) of 60 um. In the experiment we measured both the effect on the beam of the structure wakefield and the spectral properties of the radiation excited by the beam. We began by injecting a relatively long beam compared to the wavelength of the radiation, but with short rise time, to excite the structure, and then used a downstream spectrometer to infer the radiation wavelength. This was followed by injecting a shorter bunch, and then using an interferometer (also downstream of the corrugated pipe) to measure the spectrum of the induced THz radiation. For the THz pulse we obtain and compare with calculations: the central frequency, the bandwidth, and the spectral power---compared to a diffraction radiation background signal.
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A method for producing narrow-band THz radiation proposes passing an ultra-relativistic beam through a metallic pipe with small periodic corrugations. We present results of a measurement of such an arrangement at Brookhavens Accelerator Test Facility (ATF). Our pipe was copper and was 5 cm long; the aperture was cylindrically symmetric, with a 1 mm (radius) bore and a corrugation depth (peak-to-peak) of 60 um. In the experiment we measured both the effect on the beam of the structure wakefield and the spectral properties of the radiation excited by the beam. We began by injecting a relatively long beam compared to the wavelength of the radiation to excite the structure, and then used a downstream spectrometer to infer the radiation wavelength. This was followed by injecting a shorter bunch, and then using an interferometer (also downstream of the corrugated pipe) to measure the spectrum of the induced THz radiation.
Dielectric structures driven by laser-generated terahertz (THz) pulses may hold the key to overcoming the technological limitations of conventional particle accelerators and with recent experimental demonstrations of acceleration, compression and streaking of low-energy (sub-100 keV) electron beams, operation at relativistic beam energies is now essential to realize the full potential of THz-driven structures. We present the first THz-driven linear acceleration of relativistic 35 MeV electron bunches, exploiting the collinear excitation of a dielectric-lined waveguide driven by the longitudinal electric field component of polarization-tailored, narrowband THz pulses. Our results pave the way to unprecedented control over relativistic electron beams, providing bunch compression for ultrafast electron diffraction, energy manipulation for bunch diagnostics, and ultimately delivering high-field gradients for compact THz-driven particle acceleration.
We consider electromagnetic radiation of a charged particle bunch moving uniformly along a corrugated planar metallic surface. It is assumed that the wavelengths under consideration are much larger than the period and the depth of corrugation. Using the method of the equivalent boundary conditions we obtain the Fourier-transform of the Hertz vector. It is demonstrated that the ultra-relativistic bunch excites the surface waves, whereas the volume radiation is absent. Fourier-transforms of the surface wave components and spectral density of energy losses are obtained and analyzed.
A problem of diffraction of a symmetrical transverse magnetic mode $ text{TM}_{0l} $ by an open-ended cylindrical waveguide corrugated inside is considered. A depth and a period of corrugations are supposed to be much less than the wavelength and the waveguide radius. Therefore a corrugated waveguide wall can be described in terms of equivalent boundary conditions, i.e. a corresponding impedance boundary condition can be applied. Both vacuum case and the case of uniform dielectric filling of the waveguide is considered. The diffraction problem is solved using the modified tayloring technique in Jones formulation. Solution of the Wiener-Hopf-Fock equation of the problem is used to obtain an infinite linear system for reflection coefficients, the latter can be solved numerically using the reduction technique.
We investigate radiation of a charged particle bunch moving through a corrugated planar conductive surface. It is assumed that the corrugation period and depth are much less than the wavelengths under consideration. In this case, the corrugated structure can be replaced with some smooth surface on which the so-called equivalent boundary conditions (EBC) are fulfilled. Using the EBC method we obtain expressions for the electromagnetic field of the bunch which are presented in form of spectral integrals. It is demonstrated that the bunch generates surface waves propagating along the corrugations with the light velocity. Also we present results of numerical calculations for electromagnetic field components of surface waves depending on coordinates and show that these dependences can be used for determination of the bunch size.
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