Sub-THz radiation from dielectric capillaries with reflectors

In this report we present experimental investigations of THz radiation generated from a corrugated and a non-corrugated capillary with reflectors, using a femtosecond electron beam of LUCX accelerator at KEK, Japan. We discuss measurements of radiation angular distributions and their comparison with Particle In Cell simulations, and also investigate an off-central propagation of the beam in the capillaries based on experimental measurements and simulations.Comment: 5 pages, 5 figure

Laserwire at the Accelerator Test Facility 2 with Sub-Micrometre Resolution

A laserwire transverse electron beam size measurement system has been developed and operated at the Accelerator Test Facility 2 (ATF2) at KEK. Special electron beam optics were developed to create an approximately 1 x 100 {\mu}m (vertical x horizontal) electron beam at the laserwire location, which was profiled using a 150 mJ, 71 ps laser pulse with a wavelength of 532 nm. The precise characterisation of the laser propagation allows the non-Gaussian transverse profiles of the electron beam caused by the laser divergence to be deconvolved. A minimum vertical electron beam size of 1.07 ${\pm}$ 0.06 (stat.) ${\pm}$ 0.05 (sys.) {\mu}m was measured. A vertically focussing quadrupole just before the laserwire was varied whilst making laserwire measurements and the projected vertical emittance was measured to be 82.56 ${\pm}$ 3.04 pm rad.Comment: 17 pages, 26 figures, submitted to Phys. Rev. ST Accel. Beam

Radiation of a Charge Exiting Open-Ended Waveguide with Dielectric Filling

We consider a semi-infinite open-ended cylindrical waveguide with uniform dielectric filling placed into collinear infinite vacuum waveguide with larger radius. Electromagnetic field produced by a point charge or Gaussian bunch moving along structure's axis from the dielectric waveguide into the vacuum one is investigated. We utilize the modified residue-calculus technique and obtain rigorous analytical solution of the problem by determining coefficients of mode excitation in each subarea of the structure. Numerical simulations in CST Particle Studio are also performed and an excellent agreement between analytical and simulated results is shown. The main attention is paid to analysis of Cherenkov radiation generated in the inner dielectric waveguide and penetrated into vacuum regions of the outer waveguide. The discussed structure can be used for generation of Terahertz radiation by modulated bunches (bunch trains) by means of high-order Cherenkov modes. In this case, numerical simulations becomes difficult while the developed analytical technique allows for efficient calculation of the radiation characteristics.Comment: 13 pages, 11 figure