[en] We have been developing a photocathode single-cell pillbox rf gun for future light sources since 1996 at SPring-8, to date having constantly achieved a very low dark current of 2.5 pC at the beam energy of 26 MeV with a chemical-etching processed cavity. For the last four years, we have been focusing on the development of a stable and highly qualified UV-laser source for the rf gun. The energy stability (rms) of the laser has been improved down to 0.2-0.3% at the fundamental and 0.7-1.4 % at the third harmonic generation. This stability has been held for five months (Flash lamp have to be changed every two months) continuously, 24 hours a day. The improvement is the result of being able to stabilize the laser system in a humidity-controlled clean room. In addition, the ideal spatial and temporal profiles of a shot-by-shot single laser pulse are essential to suppress the emittance growth of the electron beam from the rf gun. We prepared a deformable mirror for spatial shaping and an UV-pulse stacker for temporal shaping. In the first test of 3D-laser shaping, we obtained a minimum horizontal normalized emittance of 3.05 π mm mrad with a beam energy of 26 MeV, holding its net charge to 1.0 nC/bunch. We applied the Q-scan method to evaluate the emittance. The 3D shape of the laser was spatially top-hat (flattop) one with a diameter of 1.1 mm on the cathode and temporally a squarely stacked pulse with pulse with pulse duration of 10 ps (FWHM). In this study, we demonstrate 3D (both temporal (1D) and spatial (2D) short pulse (5-20 ps) laser beam) shaping as an ideal light source for stable generation of a low emittance electron beam at a high charge (1-2 nC/bunch). (author)

[en] A damped structure with circumferential slots for the higher order mode damping has been investigated aiming at a multi-cell accelerating structure of the JLC X-band linac. The damping characteristics of this periodic structure were studied in this paper. In order to evaluate the wakefield in the periodic structure, the dispersion relations of the higher order modes were calculated by using a computer code, MAFIA. The external Q values of the resonant mode with the same phase velocity as the beam were obtained by a simulation based on Slater's tuning method. The external Q values of the longitudinal higher order modes were also evaluated. A time domain simulation was performed and found consistent with that by Slater's tuning method. (author)

[en] Energy distributions of π⁺ electroproduced on ⁶Li, ⁹Be and ²⁸Si were measured at the electron energy of about 200 MeV. The photon difference method was applied to these (e,π⁺) spectra in order to extract the (γ,π⁺) cross sections. Present results and previously obtained data show considerable contribution from several discrete levels of the residual nuclei. The spin-isospin flip giant resonance in residual nuclei could be studied up to about 20 MeV residual excitation except in ⁶Li which showed a small quasi-free and/or continuum contribution. In ⁹Be and ²⁸Si, the present results show giant resonances in the residual nuclei with a width of about 15 MeV in the gross shape. (author)

No abstract available

[en] Precise polarization control of the probe laser for Electro-Optic (EO), which propagate through the entire optics system, is key essential to realize the EO based bunch charge distribution measurements with high resolution and extinction ratio in cross Nicole configuration. We promote a numerical analysis for the polarization propagation with realistic optical setups and improve actual optical component properties. (author)

[en] New enriched borated aluminum alloys manufactured by melting process are developed, which resulted in supplying structural basket materials for spent nuclear fuel packagings. In this process, the borated aluminum alloys were melted in a vacuum induction furnace at elevated temperature than that of ordinary aluminum melting processes. Boron dissolves into the matrix at the temperature of 1273 K or more, and fine aluminum diboride is precipitated and uniformly dispersed upon cooling rapidity. It is confirmed that boron is homogeneously dispersed with the fine particles of approximate 5 in average size in the product. Tensile strength and creep property at elevated temperature in 1 mass-%B 6061-T651 plate and 1 mass-%B 3004 extruded rectangular pipe as structural materials are examined. It is confirmed that the both of borated aluminum alloys have stable strength and creep properties that are similar to those of ordinary aluminum alloys. (authors)

[en] A photo cathode RF gun has been studied in SPring-8 in order to obtain high density, short pulse and low emittance beam. A simulation code has developed to compare beam characteristics with experiment results. In this report, we show results of emittance comparison between experiments and simulations. Then, using this simulation code, we discuss how to reduce beam emittance of our experiment set. (author)

No abstract available

[en] We developed high-precision digital control magnet power supplies aiming at next-generation light sources such as SPring-8-II. The control system consists of a high-precision ADC circuit and an FPGA that processes proportional-integral control and pulse-width modulation. Using the system, the current ripple and long-term stability (8 hours) of the power supply are controlled within 20 ppm. The power supply can be made to fit various magnets by readily adjusting feedback parameters. We also developed a function to synchronize the timing of multi-channel outputs such as three outputs for sextupole steering magnets. The newly developed power supplies have been introduced to the next-generation 3 GeV light source, NanoTerasu. (author)

[en] To reduce dark currents from the grided thermionic electron gun of SPring-8 Linear Accelerator, cathode assemblies with two kinds of newly-designed grids have been developed. The two were a molybdenum perforated grid with a titanium coating of 0.5 μm in thickness, and an electro-polished molybdenum perforated grid, respectively. Dark current from the two newly-developed cathode assemblies and the commercial cathode assembly (Y-845, Communications and Power Industries LLC) which has been employed as the electron emitter of the gun, was measured using a dedicated measuring chamber. The chamber had a movable copper anode disk facing a mounted cathode assembly and consequently realized the same electric field on the grid surface under ultra high vacuum as that of the real electron gun. Dark current from the cathode assembly with the electro-polished grid was not detected during initial five hours after electric field of 3 MV/m in magnitude was applied on the grid. However, once the dark current generated, the dark current increased monotonously up to 8.5 x 10"-"8A in 21 hours. Dark current from the cathode assembly with the titanium-coated grid was smaller after the elapse of seven hours than that from the cathode assembly with the electro-polished grid and that from the Y-845 cathode assembly. The experimental results show the effectiveness of electro-polishing of a grid surface for dark current suppression and the possibility of titanium-coating of a grid surface for the reduction of the growth of the dark current. Measurement of dependence of dark current on bias voltage revealed that dark current from the newly-developed cathode assemblies was emitted from their grids and that dark current from the Y-845 cathode assembly was leak current from the cathode. (author)