Terunobu Nakajyo

Quantum Efficiencies of Mg Photocathode under Illumination with 3rd and 4th Harmonics Nd: LiYF4 Laser Light in RF Gun

A Mg photocathode for use in a radio-frequency gun was manufactured by a technique of hot isostatic pressing with diamond polishing and tested under a peak electric field of 57 MV/m. A laser cleaning process for the Mg cathode was developed. The quantum efficiency (QE) of the Mg cathode before and after the laser cleaning was measured under illumination with 262 nm and 349 nm laser light. A high QE of up to 1.0×10-3 was achieved under the 262 nm laser-light illumination. The QE of the Mg cathode under the 349 nm laser-light illumination was measured to be 2.2×10-5. The dependence of the QE on the electric field was measured and compared with a theoretical analysis including the Schottky effect.

INJECTOR STUDY FOR COMPACT HARD X-RAY SOURCE VIA LASER COMPTON SCATTERING

Compact hard X-ray source via laser Compton sattering has been developed in SHI and AIST. Our system has the injector and the linac and the high power laser system. The injector has a photo-cathode rf gun with a solenoid magnet. To enhance the X-ray yeild, we are planning to increase electron beam charge up to 5 nC/bunch and to make multi-bunch beam. The beam tracking simulation in the injector have been performed by changing laser spot size, laser pulse width, rf phase and solenoid field to optimize the distance between the injector and the linac for 5 nC/bunch high charge beam. In addition, high charge multi-bunch beam simulation in rf-gun cavity have been carried out to investigate the influence by the beam loading and the wake field.

Hybrid time-resolved spectroscopic system for evaluating laser material using a table-top-sized, low-jitter, 3-MeV picosecond electron-beam source with a photocathode

Hybrid time-resolved spectroscopy of laser media comparing electron-beam excitation and optically excited cases is performed using a newly developed, table-top-sized, low-jitter, 3-MeV picosecond electron-beam source with a photocathode. The properties of an electron-beam-pumped Ce3+:LiCaAlF6 (Ce:LiCAF) ultraviolet laser medium significant differ from those of an optically pumped medium.

A compact cyclotron based slow positron beam and a new positron pulsing system

Abstract A new positron pulsing system has been developed for the first time using an induction cavity. The slow positron beam is provided by using a compact cyclotron. In order to use the slow positron beam from the compact cyclotron for the analyses of material surfaces such as variable-energy positron lifetime spectroscopy, we have developed a new positron pulsing system. In the new system, slow positron beam bunching is performed by applying an induction cavity instead of a usual rf cavity. The induction cavity makes it possible to produce any kind of electric field change according to time. Hence the bunching efficiency of the induction cavity should be higher than that of rf cavity which can produce only sine curves electric field change according to time. In a preliminary slow positron beam bunching test using the induction cavity, a pulse width (FWHM) of about 1 ns has been achieved. A fine tuning for achieving a pulse width of 150 ps is in progress. Another new compact cyclotron and a new slow positron beam facility are also under construction next to the present ones. The design of the new facility will be also reported.

Development of high-brightness hard x-ray source by Laser-Compton scattering

Laser-Compton scattering is a promising method for generating high-brightness, ultrashort, energy-tunable X-rays. We have developed a compact X-ray source using laser-Compton scattering. Hard X-rays, ranging from 15 keV to 34 keV, were generated with a low-emittance, 38 MeV, 0.8 nC electron accelerator and a femtosecond 4TW Ti:sapphire laser. The created X-rays were composed of 2×106 (5×105) photons/pulse for interaction angles between an electron bunch and a laser pulse of 165° (90°). A highly accurate timing synchronization scheme was employed, and the fluctuation of the generated X-rays was suppressed to 11% (rms) for the 90° scattering. The spatial (angular) distributions for the intensity and the energy of the generated X-ray were measured, and agreed well with theoretical calculations. Thus, X-ray imaging has been demonstrated using a phase-contrast technique with the interference of an X-ray beam.

Laser microprobe and resonant laser ablation for depth profile measurements of hydrogen isotope atoms contained in graphite

We measured the depth profile of hydrogen atoms in graphite by laser microprobing combined with resonant laser ablation. Deuterium-implanted graphite was employed for the measurements. The sample was ablated by a tunable laser with a wavelength corresponding to the resonant wavelength of 1S-2S of deuterium with two-photon excitation. The ablated deuterium was ionized by a 2 + 1 resonant ionization process. The ions were analyzed by a time-of-flight mass spectrometer. The deuterium ions were detected clearly with the resonant ablation. The detection limit was estimated to be less than 10(16) atoms/cm(3) in our experiments. We determined the depth profile by considering the etching profile and the etching rate. The depth profile agreed well with Monte Carlo simulations to within a precision of 23 mum for the center position and 4-mum precision for distributions for three different implantation depths.

Two-Dimensional Measurements of X-ray Spectra Generated by Laser-Compton Scattering

Measurements of X-ray spectra generated by laser-Compton scattering are described. Basically, laser-Compton X-rays present distinctive characteristics, such as good-directivity, tunability, and a quasi-monochromatic X-ray spectrum. However, the actual X-ray spectrum is degraded by the effects of the broad spectrum of the laser pulse, and by the intrinsic spatial divergence of the electron bunch defined by the beam emittance. It is important to measure the spectral properties of laser-Compton X-rays for applications involving protein crystallography or mammography. The energy distribution in the forward direction can be observed using a front-illuminated deep-depletion X-ray charge-coupled device (CCD) detector. The spectral width of the measured X-rays within a detection angle of 4 mrad is estimated to be 5.0% (rms) for a CCD resolution of 2.6% (rms). These results can be accurately explained using a simple relationship between the electrons and the laser beam parameters.

The SHI slow positron beam pulsing system using an induction cavity

Abstract We have developed a new slow positron beam pulsing system for the first time using an induction cavity. In the new system, slow positron beam bunching is performed by applying an induction cavity instead of a usual rf cavity. The induction cavity makes it possible to produce any kind of electric field change according to time. Hence the bunching efficiency of the induction cavity should be higher than that of the rf cavity which can produce only sine curves electric field change according to time. Variable-energy positron lifetime spectroscopy with the new slow positron beam pulsing system has been arranged. By using the new system, the positron lifetime in Cz–Si has been measured. A difference in positron lifetime between proton-irradiated and unirradiated Cz–Si has been observed. Hence proton induced defects in Cz–Si have been detected by using our new system.

Performance of compact pulse radiolysis system using a photocathode RF gun

A compact pulse radiolysis system using a photocathode RF gun was installed at Sumitomo Heavy Industries. Some performance tests were conducted concerning the electron beam and the laser pulse. The energy and the per-pulse charge of the electron beam were measured to be 1.75 MeV max. and 1 nC. The fluctuation of the charge was restricted within 2%. The pulse widths of the electron pulse and the analyzing laser pulse were 20 ps and 15 ps, respectively. The timing jitter between electron pulse and the laser pulse was ±5.7 ps. Based on these measurements, the all-over time resolution can deduced to be about 25 ps.

A short-pulse hard x-ray source with compact electron linac via laser-Compton scattering for medical and industrial radiography

An intense, quasi-monochromatic hard X-ray beam has been generated via the laser-Compton scattering of an electron bunch with a laser pulse. An s-band linear accelerator of 40 MeV and Ti:sapphire femtosecond terawatt laser were used to generate X-rays. We plan to increase the X-ray intensity up to two-orders than the current one until FY2008. Specifications of the electron accelerator and the laser systems are presented, together with the developments and modifications being undergone.