Sokendai, Ibaraki, Japan
KEK, Ibaraki, Japan
LAL, Orsay, France
Waseda University, Tokyo, Japan
Laser-Compton scattering has become an important technique for beam diagnostics of the latest accelerators. In order to develop technologies for low emittance beams, an Accelerator Test facility (ATF) was built at KEK. It consists of an electron linac, a damping ring in which beam emittance is reduced, and an extraction line. For emittance measurement we are developing a new type of beam profile monitor which works on the principle of inverse Compton scattering between electron and laser light. In order to achieve effective collision of photon and electron, a pulsed and very thin size laser is required. Laser wire is one technique of measuring a small beam size. With green lasers, which are converted to second harmonics from IR pulsed laser, minimum beam waist is half of the beam waist obtained using infrared (IR) laser oscillator. Therefore, it is possible to obtain beam waist less than 5 μm using green laser pulse, which is required for effective photon-electron collision. First, pulsed IR seed laser is amplified with 1.5 meter long PCF based amplifier system. This pulsed IR laser is converted to second harmonics with a non-linear crystal. Pulsed green laser is injected inside four mirror optical cavity to obtain very small beam waist at interaction point (IP). Using a pulsed compact laser wire, we can measure 10 um electron beams in vertical directions. We report the development of the pulsed green laser and parameters of compact four mirror optical cavity for effective inverse Compton scattering.
AIST, Ibaraki, Japan
Waseda University, Tokyo, Japan
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
Diffraction radiation (DR), which is closely related to transition radiation, is emitted when an electron passes near an edge or interface between two media with different dielectric constants. Theoretical and experimental investigation of DR is widely performing for a non-intercepting electron beam diagnostic. We have developed an electron bunch length and a beam position monitor using a coherent diffraction radiation (CDR), which is in the range of sub-millimeter wavelength. The frequency spectrum of CDR depends on a form factor expressed as the Fourier transform of the longitudinal particle distribution. We have measured the spatial intensity distribution of CDR emitted from the metallic edge with a terahertz camera. Total intensity passing through band pass filters (BPFs) was decreased as the transmission frequency of BPFs is increased up to 6 THz. The result indicates that the bunch length is few hundreds of femtosecond. A detailed data analysis is now performing. On the other hand, we have measured the intensity distribution of CDR emitted from the metallic rectangular slit. Bow-tie intensity distribution, aligned along the perpendicular direction to the slit edge, was measured with the terahertz camera. Moreover, when the electron beam did not pass through the center of the slit, an asymmetrical intensity distribution appeared. This asymmetry is due to the pre-wave zone effect. In short, we can found the beam position to the slit by measuring the asymmetry. In this conference, we will present the experimental results.