J. Urakawa

Efficient Propagation of Polarization from Laser Photons to Positrons through Compton Scattering and Electron-Positron Pair Creation

We have demonstrated for the first time the production of highly polarized short-pulse positrons with a finite energy spread in accordance with a new scheme that consists of two-quantum processes, such as inverse Compton scattering and electron-positron pair creation. Using a circularly polarized laser beam of 532 nm scattered off a high-quality, 1.28 GeV electron beam, we have obtained polarized positrons with an intensity of 2 x 10(4) e+ /bunch. The magnitude of positron polarization has been determined to be 73 +/- 15(stat) +/- 19(syst)% by means of a newly designed positron polarimeter.

Design of a polarized positron source for linear colliders

We propose a design of a polarized positron source for linear colliders. The design is based on electron–positron pair creation from polarized g-rays which are produced by Compton scattering of circularly polarized laser light off a highenergy electron beam. Polarized positrons are created from those g-rays incident on a thin conversion target. A future linear collider of the TeV-energy region requires an extraordinary large number of positrons (B1 � 10 10 positrons/ bunch) in a multi-bunch time structure. To meet these requirements, our design employs a high-current, low-emittance electron beam of 5:8 GeV; 10 CO2 lasers, and 200 laser–electron collision-points. At each collision point, a pair of specially designed parabolic mirrors is installed to achieve efficient head-on collisions. This system allows us to produce high-intensity polarized g-rays, which effectively generate high-intensity polarized positrons with the magnitude of polarization greater than 50%: r 2003 Elsevier Science B.V. All rights reserved.

Observation of High Intensity X-Rays in Inverse Compton Scattering Experiment

Abstract We report the first results of high-intensity X-ray generation using Inverse Laser Compton scattering. This experiment was carried out by a US–Japan collaboration at the Brookhaven National Laboratory (BNL) Accelerator Test Facility (ATF) in September 1999. The 3.5 ps X-ray pulse at 6.5 keV, containing 3×10 6 X-ray photons was generated by the interaction of 60 MeV, 0.5 nC electron bunches and CO 2 laser pulses of 600 MW peak power.

Feasibility of optical diffraction radiation for a non-invasive low-emittance beam diagnostics

Abstract A “proof-of-principle” experiment on the optical diffraction radiation (ODR) as a single-pulse beam profile monitor is planned using an electron beam extracted from the KEK-ATF damping ring. The main goals of this experiment are the following: (i) To measure the yield and the angular distributions of the optical diffraction radiation from a large-size target at different wavelengths, impact parameters and beam characteristics for a comparison with analogous characteristics of optical transition radiation from a foil with identical optical parameters and for a verification of the model assumption (perfectly conducting semi-infinite target). (ii) To investigate the ODR angular distributions from a tilted target with a slit for observing the interference effects. (iii) To compare the results obtained by simulations based on classical approaches, taking into account the optical characteristics of the equipment and the beam parameters. (iv) To estimate the prospects of using ODR as a new non-invasive tool for ultrarelativistic beams. We estimated that the ODR photon yield in 10% bandwidth for 500 nm is about 106 photons/bunch with an impact parameter of 100 μm . This indicates that the ODR monitor is a promising candidate for single-pulse beam-profile measurements, and that it will be an extremely useful instrument for future linear colliders (JLC, NLC, TESLA and CLIC).

Production of gamma rays by pulsed laser beam Compton scattering off GeV-electrons using a non-planar four-mirror optical cavity

As part of the positron source R&D for future e+−e− colliders and Compton based compact light sources, a high finesse non-planar four-mirror Fabry-Perot cavity has recently been installed at the ATF (KEK, Tsukuba, Japan) [1]. The first measurements of the gamma ray flux produced with a such cavity using a pulsed laser is presented here. We demonstrate the production of a flux of 2.7 ± 0.2 gamma rays per bunch crossing ( ~ 3 × 106 gammas per second) during the commissioning.

Polarized positron source for the linear collider, JLC

Abstract A comprehensive description of a polarized positron project is presented in terms of physics motivations for utilizing a polarized positron in electron–positron collider experiments, a proof-of-principle experiment and a conceptual design of a polarized positron source for the future linear collider JLC. In order to verify a proposed method of creating highly polarized positron beams via successive two fundamental processes, i.e. Compton scattering and pair creation, we have been performing basic experiments both at KEK and BNL. First observation of positrons was made at KEK using an electron beam of 1.26 GeV and a laser of 2.33 eV. High-intensity picosecond X-rays were also generated at BNL using a specially designed Compton chamber. In order to realize polarized positron beams of the JLC which have considerably high intensity, i.e. 0.7×10 10 e + / pulse and a complicated multi-bunch structure, we have achieved a possible scheme for the Compton scattering system and a positron capture section into an L-band linac.

Cavity beam position monitor system for the Accelerator Test Facility 2

The Accelerator Test Facility 2 (ATF2) is a scaled demonstrator system for final focus beam lines of linear high energy colliders. This paper describes the high resolution cavity beam position monitor (BPM) system, which is a part of the ATF2 diagnostics. Two types of cavity BPMs are used, C-band operating at 6.423 GHz, and S-band at 2.888 GHz with an increased beam aperture. The cavities, electronics, and digital processing are described. The resolution of the C-band system with attenuators was determined to be approximately 250 nm and 1 � m for the S-band system. Without attenuation the best recorded C-band cavity resolution was 27 nm.

Intrabeam scattering analysis of measurements at KEK’s Accelerator Test Facility damping ring

We derive a simple relation for estimating the relative emittance growth in

Intrabeam scattering analysis of ATF beam measurements

x

Impedance Analysis of Bunch Length Measurements at the ATF Damping Ring

and