Junji Urakawa

SR monitor for the ATF damping ring

The ATF Damping Ring (ATF DR) aims to demonstrate the technical feasibility of a low-energy part of next-generation electron-positron linear colliders by producing an electron bunch train with extremely small emittance. To diagnose the beam profile and radiation damping there, a synchrotron radiation (SR) monitor which uses visible light has been designed and built. This paper presents the system configuration of this SR monitor and the preliminary results from the initial beam commissioning.

Backward Compton scattering of picosecond CO/sub 2/ laser pulses using relativistic electron beam for the bright X-ray generation

Laser-Compton scattering can generate X-rays or γ-rays with high brightness by applying high-peak-power laser pulses to relativistic electron bunches. We have proposed laser-Compton scattering to generate polarized γ-rays which can induce pair-creation to produce polarized positrons for JLC (Japan Linear Collider) project. As a photon source of the Compton scattering, a picosecond CO/sub 2/ laser system is going to be applied for our experiment because of the higher scattering cross section than near-infrared solid-state lasers, laser power scalability, the laser efficiency and the possibility of high-repetition rated operation. In our experiment, CO/sub 2/ laser pulses with a pulsewidth of about 180 ps are generated by the optical semiconductor slicing method. The sliced CO/sub 2/ pulses are amplified up to 6 GW by a regenerative amplifier with a high-pressure TE CO/sub 2/ laser system.

Enhancement of laser-Compton X-ray by Crab crossing

Crab crossing of electron beam and laser pulse enables head-on collision in laser-Compton scattering. We will report prospects of crab crossing laser-Compton scattering and a suitable laser system based on a thin-disk regenerative amplifier.

Novel Approach to the Elimination of Background Radiation in a Single-Shot Longitudinal Beam Profile Monitor

It is proposed to use the polarization of coherent SmithPurcell radiation (cSPr) to distinguish between the cSPr signal and background radiation in a single-shot longitudinal bunch profile monitor. A preliminary measurement of the polarization has been carried out using a 1 mm periodic metallic grating installed at the 8 MeV electron accelerator LUCX, KEK (Japan). The measured degree of polarization at θ = 90° (300 GHz) is 72.6 ± 3.7%. To make a thorough test of the theoretical model, measurements of the degree of polarization must be taken at more emission angles equivalent to more frequencies.

Investigation of the Coherent Cherenkov Radiation Using Tilted Electron Bunch

Cherenkov radiation can be produced when the velocity of the charged particles are faster than the light in some medium. We investigated the coherent Cherenkov radiation using electron bunch tilting for matching the wave front of the Cherenkov radiation. The electron bunch was tilted by using rf transverse deflecting cavity. We tested several materials for the Cherenkov target which has enough transmittance at the wavelength of THz region. As a result, high peak power THz was achieved using this novel technique. We will report the principle of this technique, the experimental results and future prospects at the conference.

Development of the Laser System for the Proof-of-Principle Experiment of Crab Crossing Laser-Compton Scattering

An X-ray source via laser-Compton scattering has the advantage of small source, energy tunability and quasi-monochromaticity and is expected to be applied in a wide range of fields such as the industry and medical care. In laser-Compton scattering, the luminosity, which represents the collision frequency between the electrons and the photons, is very important. Increasing the luminosity is strongly required for increasing the scattered photon flux. One way to increase the luminosity is tilting electron bunches at the collision point, which is called crab crossing. It is the way to create the head-on collision artificially. The purpose of this study is the proof-of-principle of the crab crossing laser-Compton scattering. In this conference, we will report the design optimization and construction of the laser system for the collision and future prospects.