Masaru Sawamura

Diffraction of γ-rays with energies of 1.17 and 1.33 MeV by a flat Si crystal

Diffraction of γ-rays by a flat Si crystal has been demonstrated using a high flux 60Co source with an intensity of 2.3 TBq. The diffraction intensities of the γ-rays with energies of 1.17 and 1.33 MeV have been measured as a function of the rotation angle of the crystal. Three peaks corresponding to the Si(440) and Si(220) diffractions for 1.17 MeV and the Si(440) diffraction for 1.33 MeV have been measured. The heights and shapes of these three peaks are well reproduced by taking into account Braggs law and the experimental geometry.

Status of R&D efforts toward the ERL-based future light source in Japan

The energy recovery linac is a very promising synchrotron light source in future. We are contemplating to realize a ERL_based next generation light source in Japan, under a collaboration between KEK, JAEA, ISSP, and other SR institutes. To this end, we started R&D efforts on its key technologies, including a low-emittance photocathode gun and superconducting cavities. We also plan to assemble these technologies into a small test ERL, and to demonstrate their operations. We report our R&D status.

Quadrupole HOM damping with eccentric-fluted beam pipes

An eccentric-fluted beam pipe was proposed to damp quadrupole modes. The eccentric-flute acts as a mode converter from quadrupole to dipole. Optimized parameters permit to damp both degenerate modes of the quadrupole with the eccentric-flute. External Q-values measured with a low power model agreed well with those calculated with MAFIA.

Second Harmonic Generation in CdTe Plate by Free Electron Laser

The second harmonic generation (SHG) signal converted from the 22 µm input wavelength of free electron laser (FEL) is observed using a non-birefringent CdTe crystal. The conversion efficiency of SHG is experimentally obtained to be ~3×10-5%/(MWcm-2).

Fabrication of Superconducting Spoke Cavity for Compact Photon Source

We are developing electron beam drivers used for laser Compton scattered (LCS) photon sources. For realizing a wide use of LCS X-ray and uf067-ray sources in academic and industrial applications, we adopt the superconducting spoke cavity to electron beam drivers. The spoke cavity has advantages such as relative compactness in comparison with an elliptical cavity of the same frequency, robustness with respect to manufacturing inaccuracy due to its strong cell-to-cell coupling, the better packing in a linac to install couplers on outer conductor. On the other hand the spoke cavity has disadvantage of more complicated structure than an elliptical cavity. Though our proposal design for the photon source consists of the 325 MHz spoke cavities in 4K operation, we have begun to fabricate the half scale model of 650 MHz spoke cavity in order to accumulate our cavity production experience by effective utilization of our limited resources. We fabricated the die set, performed press forming test and measured the formed shape. In this paper, we present our fabrication status.

Enhanced diffraction of MeV γ-rays by mosaic crystals

The diffraction of γ-rays by mosaic Si crystals with thicknesses of 20, 40, and 80 mm and by a 2-mm-thick perfect Si crystal in a transmission Laue geometry was measured using a high-flux 60Co source with an intensity of 2.2 TBq. The measured diffraction intensities at 1.17 and 1.33 MeV using 40- and 80-mm-thick mosaic crystals were enhanced by a factor of approximately 8.6 compared with those of the perfect Si crystal. The integrated reflectivity is well described in statistical dynamical theory by taking into account γ-ray absorption inside the crystals.

Multipactor Simulations in 650 MHz Superconducting Spoke Cavity for an Electron Accelerator

To realize a compact industrial-use X-ray source with the laser-Compton scattering, a 325MHz superconducting spoke cavity for an electron accelerator operated at 4K is under development. Design-optimizations of the first prototype cavity were finished. Multipactor simulations were carried out as parts of optimization efforts. In this paper, procedures of multipactor simulations by using CST studio suite are briefly introduced. Then results of simulations and analyses to extract an optimum geometry are presented. A relation between a cavity geometry and an intensity of multipactor is also commented.

Design and Development of Superconducting Spoke Cavity for Compact Photon Source

The spoke cavity is expected to have advantages for compact ERL accelerator for X/uf067-ray source based on laser Compton scattering. We have been developing the spoke cavity under a research program of MEXT, Japan to establish the fabrication process. Since our designed shape of the spoke cavity is complicated due to optimization of the RF properties, we have been designing the mold including the process of press forming and the support parts for vacuum tolerance with the mechanical simulation. In this paper we present status of the spoke cavity fabrication.

Measurement of beam position monitor using HOM couplers of superconducting cavities

The offset beam from the axis induces the HOMs in the cavities. These HOMs in superconducting cavities are usually damped by HOM couplers to suppress the beam instability. The induced HOM field of dipole mode is proportional to the beam offset and can be used to measure the beam position inside the cavity. Measuring the HOM power by scanning the beam permits to estimate the beam position using a known function of the HOM power. The steering magnet was installed to the JAEA superconducting ERL-FEL to vary the beam position. The beam position in the cavity was estimated with the measured HOM power from the HOM coupler.