Satoshi Hashimoto

Abstract The intensity and energy spatial distributions of collimated laser Compton scattering (LCS) γ-ray beams and of the associated bremsstrahlung beams have been investigated as functions of the electron beam energy, electron beam phase space distribution, laser optics conditions and laser polarization. We show that the beam halo is affected to different extents by variations in the above listed parameters. In the present work, we have used laser Compton scattering simulations performed with the eliLaBr code (https://github.com/dan-mihai-filipescu/eliLaBr) and real LCS and bremsstrahlung γ-ray beams produced at the NewSUBARU synchrotron radiation facility. A 500 μm MiniPIX X-ray camera was used as beamspot monitor in a wide γ-ray beam energy range between 1.73 MeV and 38.1 MeV.

An undulator generating a magnetic field whose longitudinal profile is arbitrarily varied has been developed, which is one of the key components in a number of proposed new concepts in free-electron lasers. The undulator is composed of magnet modules, each of which corresponds to a single undulator period, and is driven by a linear actuator to change the magnetic gap independently. To relax the requirement on the actuator, the mechanical load on each module due to magnetic force acting from opponent and adjacent modules is reduced by means of two kinds of spring systems. The performance of the constructed undulator has been successfully demonstrated by magnetic measurement and characterization of synchrotron radiation.

Current gamma-ray telescopes based on photon conversions to electron-positron pairs, such as Fermi, use tungsten converters. They suffer of limited angular resolution at low energies, and their sensitivity drops below 1 GeV. The low multiple scattering in a gaseous detector gives access to higher angular resolution in the MeV-GeV range, and to the linear polarisation of the photons through the azimuthal angle of the electron-positron pair. HARPO is an R&D programme to characterise the operation of a TPC (Time Projection Chamber) as a high angular-resolution and sensitivity telescope and polarimeter for gamma rays from cosmic sources. It represents a first step towards a future space instrument. A 30 cm cubic TPC demonstrator was built, and filled with 2 bar argon-based gas. It was put in a polarised gamma-ray beam at the NewSUBARU accelerator in Japan in November 2014. Data were taken at different photon energies from 1.7 MeV to 74 MeV, and with different polarisation configurations. The electronics setup is described, with an emphasis on the trigger system. The event reconstruction algorithm is quickly described, and preliminary measurements of the polarisation of 11 MeV photons are shown. (C) 2016 Elsevier B.V. All rights reserved.

© 2016 Atomic Energy Society of Japan. All rights reserved. We have proposed a new selective isotope transmutation method using photonuclear reactions with quasi-monochromatic γ-ray beams. This method is based on the fact that the particle threshold of a long-lived fission product (LLFP) such as 93Zr, 107Pd, or 79Se is lower than those of stable isotopes of the same chemical element. Therefore, this method has the excellent advantage that LLFPs cannot, in principle, be produced newly even if the target materials include stable isotopes in addition to LLFPs. Furthermore, this method is effective for 126Sn, 135, 137Cs, 90Sr, and 3H. The nuclear data involved and suitable γ-ray sources are discussed. Laser Compton scattering γ-ray sources and neutron capture γ-rays in nuclear reactors are candidates for this method.

Current gamma-ray telescopes suffer from a gap in sensitivity in the energy range between 100 keV and 100 MeV, and no polarisation measurement has ever been done on cosmic sources above 1 MeV. Past and present e(+)e(-) pair telescopes are limited at lower energies by the multiple scattering of electrons in passive tungsten converter plates. This results in low angular resolution, and, consequently, a drop in sensitivity to point sources below 1 GeV. The polarisation information, which is carried by the azimuthal angle of the conversion plane, is lost for the same reasons. HARPO (Hermetic ARgon POlarimeter) is an R&D program to characterise the operation of a gaseous detector (a Time Projection Chamber or TPC) as a high angular-resolution and sensitivity telescope and polarimeter for gamma rays from cosmic sources. It represents a first step towards a future space instrument in the MeV-GeV range. We built and characterised a 30cm cubic demonstrator [SPIE 91441M], and put it in a polarised gamma-ray beam at the NewSUBARU accelerator in Japan. Data were taken at photon energies from 1.74 MeV to 74 MeV and with different polarisation configurations. We describe the experimental setup in beam. We then describe the software we developed to reconstruct the photon conversion events, with special focus on low energies. We also describe the thorough simulation of the detector used to compare results. Finally we will present the performance of the detector as extracted from this analysis and preliminary measurements of the polarisation asymmetry. This beam-test qualification of a gas TPC prototype in a gamma-ray beam could open the way to high-performance gamma-ray astronomy and polarimetry in the MeV-GeV energy range in the near future.

We designed and built an experimental apparatus based on a time projection chamber, a novel scheme for high performance gamma-ray astronomy and polarimetry in the gamma -> e(+)e(-) regime. This presentation focuses on the electronics aspect of the detector and, in particular, on the versatile dedicated trigger system that we have developed which allowed us to take data on beam with a high gamma-conversion signal efficiency and a high rejection factor for single tracks and upstream conversion background events. Our scheme allows for the selective collection of gamma conversions in a high-background-rate environment, such as that which is present in orbit, with a fine 3D imaging of the events and very low (in particular electronics) background, at a mild cost in terms of the number of electronics channels and therefore of electrical power consumption.

Tunable and high-power terahertz radiation sources using relativistic electron beams from a compact linear accelerator (LEENA) are under development. Synchrotron radiation and Smith-Purcell radiation in the THz region were successfully measured. The coherent radiation power from an electron bunch shorter than 1 ps is estimated theoretically to be about 10(7) larger than the incoherent power. Recent experimental results on the generation of THz radiation and numerical results on high-power coherent radiation from a short electron bunch are reported. (C) 2016 Wiley Periodicals, Inc.

A time projection chamber (TPC) can be used to measure the polarization of gamma rays with excellent angular precision and sensitivity in the MeV-GeV energy range through the conversion of photons to e(+)e(-) pairs. The Hermetic ARgon POlarimeter (HARPO) prototype was built to demonstrate this concept. It was recently tested in the polarized photon beam at the NewSUBARU facility in Japan. We present this data-taking run, which demonstrated the excellent performance of the HARPO TPC.

The synchrotron radiation facility NewSUBARU with nine beam-lines is operated by the Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Japan. Gamma-ray beams are produced in the beam-line BL01 by laser Compton scattering (LCS) from 0.5–1.5 GeV electron beams in the NewSUBARU storage ring [1]. Lasers with different wavelengths are used to produce the LCS photon beam in the energy range from 0.5 MeV to 76 MeV: a Nd:YVO&lt inf&gt 4&lt /inf&gt laser (λ = 1064 and 532 nm), a CO&lt inf&gt 2&lt /inf&gt laser (λ = 10.59 μm), and an Er fiber laser (λ = 1540 nm). A new experimental hutch, GACKO (Gamma Collaboration Hutch of Konan University), was installed in the BL01 in March 2012.

Coherent synchrotron radiation (CSR) in Tera-Hz region was observed at NewSUBARU. Three types of CSR from three types of electron beam were detected in the storage ring. One was a radiation burst from a high-density single-bunched beam. The burst had a threshold current of 1.0 nC/bunch for the normal operation parameters. The second was a quasi-dc radiation from a low current and short-bunched beam. The ring was operated in a quasi-isochronous (low momentum compaction factor) mode, which could store the short-bunched beam stationary. The bunch charge was as low as 1 pC/bunch and the bunch length was as short as 4 ps FWHM. The third was a radiation pulse following injection. A short-bunched linac beam, with a base width of 20 ps and a charge of 50 pC/bunch, emitted short-pulsed CSR in the storage ring.

Coherent synchrotron radiation from a short electron bunch in a storage ring was observed at NewSUBARU. The ring was operated with energy of 1 GeV and qusi-isochronous mode. The linear momentum compaction factor was smaller than 2x10(-5) and the bunch length was shorter than 5 ps (FWHM). An extremely powerful radiation was observed from a low current beam, and power spectrum was measured by an interferometer.

A quasi-isochronus operation is one of the operation modes of NewSUBARU, a 1.5 GeV VUV storage ring. NewSUBARU has six invert bending magnets to control the momentum compaction factor, The aim of this research is to explore the extreme reduction of electron bunch length by reducing the momentum compaction factor, which is a conventional method. We experimentally reduced the momentum compaction factor from 0.0014 down to less than 10(-5), keeping the beam in the ring. The second-order momentum compaction factor was adjusted to almost zero, while keeping the third-order momentum compaction factor positive. The ring was operated at 1.0 GeV. Using a streak camera, the shortest bunch length we observed was 4 ps FWHM.

Negative alpha-p operation has been successfully performed at 1 GeV in the NewSUBARU storage ring. Microwave and fast head tail instabilities were measured in comparison with those in the positive alpha-p case. The fundamental mechanism is well understood by the established theory based on the positive alpha-p case, but the resultant behavior is very different.

Since beam commissioning the beam instability due to ion trapping phenomena has been occasionally observed in the 1.0-1.5GeV NewSUBARU electron storage ring. In this paper we summarize the photo stimulated desorption of gas molecular and the measurements of transverse instabilities related to trapped ions in the NewSUBARU ring.

The aims of the New SUBARU project are to promote industrial applications in the VUV and soft X-ray region and to develop research and development towards new light sources. The main facility of the New SUBARU project is the 1.5 GeV electron storage ring which is under construction at the SPring-8 site in Harima Science Garden City, Japan. The storage ring is quasi-isochronous and has variable momentum dispersion for the deep study of beam dynamics in very short bunches.

A new crowbarless power supply is to be installed at the New SUBARU storage ring. A high-power switching inverter unit eliminates the need for expensive and unstable crowbar circuits for the klystron power supply. It also realizes a very small voltage ripple in the low-frequency region. This is an important characteristic, especially in a quasi-isochronous storage ring such as New SUBARU.

The main facility of the New SUBARU project is the 1.5 GeV electron storage ring which is under construction at the SPring-8 site in Harima Science Garden City. The first beam commissioning from the SPring-8 LINAC is scheduled at the end of March, 1998. The aim of new SUBARU is to promote industrial activities in the local area (Hyogo prefecture) and to develop experimental investigations for new light sources.