橋本 智

The double differential cross-sections (DDXs) of photoneutron production via the photonuclear reaction on tantalum, tungsten, and bismuth for 13 and 17 MeV linearly polarized photon beams were measured using the time-of-flight method at the NewSUBARU-BL01 facility. Polarized photons were obtained by the Laser Compton backscattering (LCS) technique. Two distinct components were observed on the spectra: the lowenergy component up to 4 MeV and the high-energy above 4 MeV. The angular distribution of the low-energy component was isotropic, whereas the high-energy was distributed anisotropically and influenced by the angle between direction of photon polarization and neutron emission, especially for 17 MeV photon energy. These phenomena were similar to those of 197Au target observed in the previous studies. The low-energy neutron distributions at 13 and 17 MeV photon energies were almost identical for all three targets. The DDX energy integration was calculated and compared among the three targets for two-photon energies. Given the horizontal polarization (plane parallel to the x-axis) of the incident photons, the emission angles of 90° on the x-axis and y-axis recorded the maximum and minimum photoneutron yield, respectively. The differences between these two positions were minor for ¹⁸¹Ta and ^natW at 13 MeV photon energy and noticeable for other cases. An underestimation of the TENDL nuclear data library was observed on the photoneutron DDXs compared to the experimental results for ¹⁸¹Ta and ²⁰⁹Bi.

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.

Access to the photon polarisation in the 1-100 MeV energy range is a challenge for the next generation of space telescopes. The current telescopes in space are almost blind in this energy range, mainly due to the degradation of the angular resolution of e+e-pair and due to elastic scattering in the matter. Pair-conversion detector technologies as gaseous detectors are a promising alternative to the technologies based on tungsten-converter/thin-sensitive-layer stacks such as COS-B/EGRET/Fermi-LAT, firstly to improve the single-photon angular resolution and secondly for the polarisation information. The use of a time projection chamber (TPC) as a target and a tracking detector will improve by up to one order of magnitude the single-photon angular resolution (0.5°@100 MeV) with respect to the Fermi-LAT (5°@100 MeV), and by up to a factor of three with respect to what can be expected for silicon detectors (1.0-1.5°@100 MeV). With such a good angular resolution, a TPC can close the sensitivity gap at the level of 10-6 MeV/cm2.s) between 3 and 300 MeV despite having e lower sensitive mass. Furthermore, this good single-track angular resolution allows us to measure the linear polarisation fraction. The HARPO (Hermetic ARgon POlarimeter) detector prototype that we built is a high pressure (0.5-4 bar) low pile-up and low-diffusion gas detector. We will present the results of its high-statistics characterisation in the 1.7-74 MeV fully-polarised and non-polarised gamma-ray beam provided by the BL01 line at NewSUBARU. The excellent value of the polarisation asymmetry dilution factor that we measured opens the possibility of having a polarimeter in space working in the MeV-GeV energy range. In conclusion, we will present the design of a balloon-flight prototype ST3G (Self-Triggered Time projection chamber as a Gamma-ray Telescope) which is being developed. We will discuss its expected performance.

電子蓄積リングを用いたレーザー・コンプトン散乱ガンマ線源において、10-40MeVの直線偏光ガンマ線による光核反応中性子の発生分布を測定した。ガンマ線ビーム軸に対して、90度方向に発生する中性子の分布が、I=a+b・cos2φの強度分布を持つことは、金、ヨウ素、銅ターゲットを用いて実証し、既に報告した。ここで、φは、ガンマ線偏光方向に対する方位角である。今回は、銀およびイットリウムターゲットを用いて、同様な巨大核共鳴領域で測定した結果に加え、Be-9ターゲットを用いて、異なる共鳴エネルギーでの計測結果を報告する。

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.

Gamma-ray astronomy enables the exploration of the non-thermal emission and magnetic field configuration of objects such as active galactic nuclei (AGN), gamma ray bursts (GRB) and pulsars. Presently, there is a sensitivity gap between 1MeV and 100MeV. Additionally, there is no polarisation measurement above 1MeV, although such a measurement could shed light on emission processes. A gaseous detector can achieve a much better angular resolution in the MeV-GeV range than the current/past telescopes that use tungsten converters, thanks to the reduced multiple scattering of the electrons and positrons. This translates to a greatly improved point source sensitivity and gives access to the linear polarisation of the photons through the azimuthal angle of the pair. The HARPO time projection chamber (TPC) is a high angular resolution telescope for gamma-ray polarimetry. It was installed in a polarised gamma-ray beam at NewSUBARU in Japan in 2014. Data were taken at photon energies from 1.7MeV to 74MeV, and with different polarisation configurations. The experimental setup of the TPC and the photon beam are described. The first results from the beam campaign are shown.

An AC sextupole magnet system was developed and installed in the electron storage ring, NewSUBARU. This system is for a proof of principle experiment of a new suppression method of transverse beam instabilities. The magnet produces a modulation of the chromaticity with a synchrotron frequency, which creates a large tune spread and suppresses instabilities with Landau damping. The rating of the system is determined from the ring parameters and the yoke length is 150 mm, the bore radius is 80 mm, the maximum field is 36 T/m2 at 300 A and the operation frequency is 4-6 kHz. The coil conductor consists of an inner side half turn (closer to the magnet axis) and an outer side half turn for each pole. At the operation with peak current of 300 A, the power loss in the magnet was 900 W. The eddy current loss in the inner side coil conductor is the main part of this loss and is induced by the magnetic field excited by the outer coil current. It has no water-cooling system and the coil temperature was raised to higher than 70°C after 5 minutes operation and the interlock system is set to turn off the power at 80°C. However this is acceptable for the experiment in a short period. To drive the current of 300 A peak, an external capacitance is attached to the magnet, which forms the LC resonant circuit that is excited by a general-purpose AC power amplifier (DC-20 kHz, 170 V peak, 23 A peak). The Q-value of the circuit is 16.5 for 5 kHz. The resonant frequency is variable by remote switching of the several capacitances. With this magnet system, we successfully observed the suppression of beam instabilities. © 2008 IEEE.

Some topics of the operational characteristics and improvements in these two years, in particular, vacuum and orbit, are summarized. The top-up operation realizes the constant flux of synchrotron radiation light at 1 GeV, then many experiments or users become to need the stability of light in less than 1 % range. The orbit stability of the electron beam is the key for this. © 2007 American Institute of Physics.

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.

The 792-MHz HOM of the RF cavity can drive horizontal coupled bunch instability in the NewSUBARU electron storage ring. Detailed characteristics of this instability were investigated by changing the HOM frequency, betatron tune, chromaticity and magnitude of the stored current at the energy of 1 GeV. The experiments were performed under the condition that the only one mode can be excited and the stored current was limited as ∼ 3.4 mA/bunch to avoid catastrophic blow up. The measured results showed saw tooth oscillation and were compared with an analytical calculation using a rigid bunch model. The co-existence of the longitudinal modes l = 0 and l = ± 1 might produce complicated beam behaviour.

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 present status of the storage ring at the synchrotron radiation (SR) facility NewsSUBARU is described. The SR facility is a light source with 1.5 GeV electron storage ring designed to generate bright light in the soft X-ray region. Three insertion devices consisting of long undulator (LU), optical klystron free electron laser (OK-FEL) and short undulator were installed in the storage ring. Anlysis suggests that an increase of beam dose on-beam decreases pressure and improves the beam lifetime.

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.