S. Okuda

Measurement of far-infrared subpicosecond coherent radiation for pulse radiolysis

Abstract Using a magnetic bunch compression method, a 26.5 MeV subpicosecond electron single bunch was generated with the L-band linac of Osaka University. The coherent transition radiation emitted from the subpicosecond single bunch was observed at wavelengths from 100 to 700 μm. The intensity was 7.9×109 times higher than that of the incoherent transition radiation obtained by calculation. The length of the compressed electron bunch was evaluated to be roughly 50 fs (rms) from the analysis of the spectra of the transition radiation. The coherent transition radiation has high enough intensity to be applied to pulse radiolysis as a pulsed light source.

Enhancement of Hydrogen Evolution Yield from Water Dispersing Nanoparticles Irradiated with Gamma-Ray

Hydrogen gas evolution from water dispersing nanoparticles induced by 60Co γ-ray irradiation was studied. Nanoparticles of TiO2 and Al2O3 with average sizes of 7–33 nm supplied from several suppliers were examined. It was indicated that reactions enhancing the hydrogen evolution proceed on particles surface. It was implied that the yield depends on size of agglomerated particle regardless of their primary particle size and chemical species. Reactions that enhance the hydrogen yields were discussed, and radiolysis process was concluded dominant in the total enhancement mechanism.

Self-amplified spontaneous emission at wavelengths of 20 and 40 μm from single-bunch electron beams

Abstract The high-brightness single-bunch electron beams of a 38-MeV L-band linac have been used for free-electron laser amplifier experiments to investigate self-amplified spontaneous emission at wavelengths of 20 and 40 μm. At a charge of electrons in a bunch of 28 nC and a pulse length of about 30 ps the intensities of radiation measured have been 5 and 100 times those of the incoherent spontaneous emission estimated at wavelengths of 20 and 40 μm, respectively. The characteristics of the radiation are discussed for developing intense pulsed light-sources.

Magnetic flux loss of the permanent magnets used for the wigglers of FELs by the irradiation with high-energy electrons or X-rays

Abstract Study was made on the irradiation effects of the permanent magnets used for the wigglers of FELs with high-energy electrons and X-rays. Four kinds of Nd–Fe–B and one kind of Sm–Co samples were irradiated with 17xa0MeV electron beams or 60Co γ-rays. The magnetic flux loss of one kind of Nd–Fe–B samples irradiated with electrons at doses below 2.1×10 −3 C / cm 2 increased with the irradiation dose. For the electron irradiation at doses of about 1.4×10 −3 C / cm 2 , magnetic flux loss was apparent for two kinds of Nd–Fe–B samples. No flux loss was observed for γ-rays at absorbed doses higher than that of the electrons. The influence of the irradiation of electrons on the magnets of a wiggler in FEL experiments is discussed.

Single-bunch and multibunch electron beam generation for FEL experiments with the 38 MeV L-band linear accelerator at ISIR

Abstract The generation of multibunch electron beams used for FEL oscillation experiments with the 38 MeV L-band linear accelerator at The Institute of Scientific and Industrial Research has been studied. Originally, the components of the accelerator system have been optimized for generating a high-brightness single-bunch beam. The operational conditions of the system have been investigated for a multibunch beam. A multibunch beam with a macropulse length of 4 μs has been accelerated at energies of 17 to 19 MeV. The latter part of the pulsed beam with a length of 1.8 μs has an energy spread of 1.8%. The charge per bunch is 2 nC. The beam of this part has been successfully used for oscillation experiments at a wavelength of 32 to 40 μm.

Mirror reversal simply explained without recourse to psychological processes

This paper proposes a simple and definitive solution to the mirror reversal problem, “Why does a mirror reverse left and right but not up and down?” The solution is given by combining the inversion caused by the optical process of mirroring and the definition of the left-right axis. Thus the left-right reversal of mirror images essentially does not involve psychological processes, in contrast to the multiprocess hypothesis recently proposed by Takano.

Free-electron laser oscillation with a multibunch electron beam of the 38 MeV L-band linear accelerator at ISIR

Abstract Free-electron laser oscillation has been achieved with a multibunch electron beam generated with the 38 MeV L-band linear accelerator at The Institute of Scientific and Industrial Research in Osaka University. The wavelengths of the observed FEL are 32 to 40 μm for energies of the electron beams of 17 to 19 MeV. The macropulse length of the beam is 1.8 μs. The net FEL gain measured at a wavelength of 40 μm is 25%. The tuning range of the length of the optical cavity and the FEL spectra have also been measured. The total output FEL energy of 12 mJ has been obtained in the recent experiments at a wavelength of 40μm. The intracavity peak power of the FEL is estimated to be about 150 MW.

Higher harmonic generation observed in SASE in the far-infrared region

Abstract The self-amplified spontaneous emission (SASE) has been generated using the single bunch electron beam of 11.3xa0MeV energy with a peak current of ∼0.5xa0kA accelerated with an L-band linac and a 1.92xa0m long, 32 period wiggler, and the wavelength spectrum of SASE has been measured in the wide wavelength region from 50 to 200xa0μm using a grating monochromator. We have observed the second harmonic peak at 90xa0μm and the third harmonic peak at 60xa0μm in the spectrum as well as the fundamental peak of SASE at 180xa0μm. Spectral widths of the fundamental, the second and the third harmonics are measured to be 2.9%, 3.6%, 5.3%, respectively. The FEL parameter is 0.032, which is estimated from the spectral width of the fundamental peak. Absolute energies per optical pulse of the fundamental, the second and the third harmonics have been derived to be 2.75xa0nJ, 73xa0pJ, 182xa0pJ, respectively, by calibrating the measurement system with a blackbody radiator. The second and the third harmonic peaks are concluded to be produced by nonlinear harmonic generation of SASE.

Wavelength spectrum of self-amplified spontaneous emission in the far-infrared region

Abstract We are conducting experiments to generate self-amplified spontaneous emission (SASE) in the far-infrared region and to measure its characteristics, using a single bunch electron beam accelerated with the L-band linac at ISIR, Osaka University. We have measured the wavelength spectra of SASE in the wavelength region between 80 and 180xa0μm using a grating monochromator and a Gexa0:xa0Ga detector. The measured spectral widths of the fundamental peak are slightly larger than those predicted by the one-dimensional model. We have also observed the second harmonic peak of SASE.

New light source in a submillimeter to millimeter range using the coherent radiation from the single-bunch electron beam at ISIR

The coherent synchrotron radiation has a continuous spectrum in a submillimeter to millimeter range and is highly intense compared with the other far-infrared light sources. A new light source was established by using the coherent radiation from the intense single-bunch electron beam generated with the 38 MeV L-band linear accelerator at The Institute of Scientic and Industrial Research, Osaka University. In the experiments the beams at an energy of 27 MeV and a charge of electrons in a bunch of 30 nC were used. The intensity, stability and polarization of the coherent synchrotron radiation were measured at wavelengths of 0.7}1.4 mm. The absorption spectroscopy was carried out for N 2 O gas. The results agreed with those obtained by calculation. The application of the pulsed radiation which is synchronized with the electron bunch, to stroboscopic pulse-radiolysis experiments is under preparation. ( 2000 Elsevier Science B.V. All rights reserved. PACS: 41.60.-m; 41.75.Ht; 42.25.Kb; 52.75.Ms