Hirotaka Shimizu

Apparatus for a search for T-violating muon polarization in stopped-kaon decays

Abstract The detector built at KEK to search for T-violating transverse muon polarization in K + → π 0 μ + ν μ ( K μ 3 ) decay of stopped kaons is described. Sensitivity to the transverse polarization component is obtained from reconstruction of the decay plane by tracking the μ+ through a toroidal spectrometer and detecting the π0 in a segmented CsI(Tl) photon calorimeter. The muon polarization was obtained from the decay positron asymmetry of muons stopped in a polarimeter. The detector included features which minimized systematic errors while maintaining high acceptance.

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.

Photon generation by laser-Compton scattering at the KEK-ATF

We performed a photon generation experiment by laser-Compton scattering at the KEK-ATF,aiming to develop a Compton based polarized positron source for linear colliders. In the experiment, laser pulses with a 357 MHz repetition rate were accumulated and their power was enhanced by up to 250 times in the Fabry-Perot optical resonant cavity. We succeeded in synchronizing the laser pulses and colliding them with the 1.3 GeV electron beam in the ATF ring while maintaining the laser pulse accumulation in the cavity. As a result, we observed 26.0 +/- 0.1 photons per electron-laser pulse crossing, which corresponds to a yield of 10(8) photons in a second

Photon Generation by Laser-Compton Scattering Using an Optical Resonant Cavity at the KEK-ATF Electron Ring

We studied gamma-ray generation by the laser-Compton scattering using a Fabry-Perot optical resonant cavity at the KEK-ATF electron storage ring. The laser power was enhanced up to 388 W in the optical resonant cavity with an injection power of 7 W in the ATF operation environments. The yield of photons for a crossing of a laser pulse and an electron bunch was 3.3 +/- 0.6, which was consistent with a numerical estimate. In this paper, we report construction, installation and future prospect toward the polarized positron generation for the International Linear Collider.

Permanent Magnet System for PET Cyclotron

The recent paper is devoted to design, manufacturing and testing the permanent magnet system to be used for Positron Emission Tomography (PET) cyclotron. The using permanent magnet material instead of copper coils allows essential electric power savings during PET cyclotron operation, though it comes to some increasing construction cost. The main problem why until now permanent magnets were not used for PET cyclotron magnet system is huge magnetic force, making cyclotron assembling/disassembling and isochronous magnetic field adjustment very difficult. For presented magnet system that problem is solved by applying rotating system providing the magnetic field switch-off (reduction to practically zero level inside working aperture). It makes assembling and adjustment easy at force free conditions. The main parameters of permanent magnet system are as follows: the average field is 1.4 T, pole radius is 375 mm and weight is 900 kg. As it shown in paper the magnetic properties of constructed permanent magnet system does satisfy to specification for magnet system of typical 10 MeV cyclotron for PET radioisotope production.

High-precision magnetic field mapping with a three-dimensional Hall probe for a T-violation experiment in Kμ3 decay

Abstract High-precision magnetic-field mapping was performed for an experiment to search for a violation of time-reversal invariance in the K + → π 0 μ + ν μ decay at the KEK proton synchrotron. A commercially available three-dimensional Hall probe was used in conjunction with a specially designed mapping device and a goniometer system. Details concerning the measurement principle, calibration, actual measurements and analysis are described.

Development of optical resonant cavities for laser-Compton scattering

Abstract We have been developing optical resonant cavities for laser-Compton scattering experiment at the Accelerator Test Facility in KEK. The main subject of the R&D is to increase laser pulse energy by coherently accumulating the pulses in an optical resonant cavity. We report previous results, current status and future prospects, including a new idea of an optical resonant cavity.

Fabrication and Evaluation of Superconducting Single-Cell Cavities Manufactured Using Various Materials and Methods

Six cavities of the same type (TESLA-like shape) made from six different niobium sources or types were produced at KEK using various materials and fabrication methods. Throughout these sequential in-house fabrications, comparisons of the properties of the various materials for use in superconducting radio-frequency cavities were conducted. The advantages and disadvantages of these properties, together with different fabrication methods, were examined. The cavities were fabricated primarily using existing facilities within KEK to control the fabrication quality. Vertical tests to evaluate single-cell cavity performances were conducted at the Superconducting RF Test Facility in KEK. The technical details of each fabrication method and the obtained high-gradient test results are described and discussed.