M. Oyamada

Coherent synchrotron radiation at submillimeter and millimeter wavelengths

Abstract To study the coherence effect of synchrotron radiation (SR), light emission from the Tohoku 300 MeV linac, whose energy and bunch length of electrons were 180 MeV and a few millimeters, was observed in the submillimeter and millimeter wavelength regions by using a grating spectrometer. The absolute intensity of ordinary SR in the visible region was also measured. In comparison with ordinary SR, the absolute intensity of SR in the millimeter wavelength region was enhanced by about a factor of 10 6 , which corresponded roughly to the number of electrons in one bunch. The intensity of enhanced SR showed the quadratic dependence on the beam current. The enhanced SR was strongly polarized in the electron orbital plane. The relation between the electron distribution in a bunch and the spectra of coherent SR is discussed.

Photo-production of neutral kaons on 12C in the threshold region

Abstract The kaon photo-production process on 12C has been studied by measuring neutral kaons in the photon energy range of 0.8–1.1 GeV. Neutral kaons were identified by the invariant mass constructed from two charged pions emitted in the K S 0 → π + π − decay channel. The differential and integrated cross sections in the threshold photon energy region were obtained. The obtained momentum spectra were compared with a Spectator model calculation using elementary amplitudes of kaon photo-production given by recent isobar models. The present results provide the first information on the n ( γ , K 0 ) Λ reaction, which is expected to play an important role in constructing models of strangeness production by electromagnetic interactions. The experimental results show that the cross section of C 12 ( γ , K 0 ) is of the same order as that of C 12 ( γ , K + ) and suggest that a slightly backward K 0 angular distribution is favored in the γ n → K 0 Λ process.

Resonance effects of transition radiation emitted from thin-foil stacks

Abstract Transmission of charged particles through a regular dielectric foil-stack intensifies transition radiation (TR) X rays owing to the intrafoil and the interfoil resonances. In order to study the effects of both resonances on energy spectra of TR, we measured the spectra for different sets of foil-stacks at several emission angles and compared them with the calculated ones. It was found that interfoil resonance modifies the energy of the peaks observed in the spectra depending on the emission angle but intrafoil resonance has little effect.

Electroexcitation of rotational bands in 25Mg

Abstract The electric quadrupole and hexadecapole excitations of 25 Mg have been investigated by inelastic electron scattering. The measured C2 and C4 form factors are compared with the strong-coupling model; good agreement is obtained.

A prebunched FEL based on coherent transition radiation in the far-infrared region

Abstract A short-bunch beam of electrons of 150 MeV is led to an open resonator of semi-confocal type. The wavepackets of coherent transition radiation (TR), emitted from bunched electrons passing through mirrors of the resonator, go back and forth in the resonator and superpose on the subsequent bunches to stimulate coherent TR. The main mode is assigned as TEM 01 , and the intensity depends on the square of the beam current. The output intensity of the resonator is compared with the coherent spontaneous TR generated within the resonator to show amplification of radiation due to the stimulated emission.

Resonance effects of transition radiation emitted from thin foil stacks using electron beam

Transition radiation (TR) X-rays are expected to be a highly brilliant X-ray source because the interference among TR X-rays emitted from many thin foils placed periodically in vacuum can increase their intensity and make them quasi-monochromatic. In order to study the interference (resonance) effects of TR, we measured the energy spectra of TR for several sets of thin foil stacks at various emission angles. It was found that the resonance effects of TR are classified into intrafoil and interfoil resonances and the intensity of TR X-rays increases nonlinearly with increasing foil number, attributed to the interfoil resonance. It became evident that the brilliance of TR is as high as that of SR.

K -shell ionization by relativistic electron impact

Abstract The K-shell X-ray production cross sections by 70,1500 and 270 MeV electron impact have been measured and compared with available theories. The scaling laws for the K-shell ionization cross section at relativistic energy range are discussed.

Construction and development of an UV free electron laser under the cooperation of Nihon U., KEK, PNC, ETL and Tohoku U.

Abstract The construction and the development of an UV free electron laser at Narashino Campus, Nihon U. have been started under the cooperation of Nihon U., KEK 1 , PNC 2 , ETL 3 and Tohoku U. The project requires a 125 MeV S-band electron linear accelerator to expand the oscillation of FEL to the UV region using fundamental mode. The injection system consists of a thermionic RF-gun with a LaB 6 cathode and a magnet for magnetic bunching. We are studying to reduce the back-bombarding electrons to realize the macropulse length of 20 μs. Electron beams, up to the energy of 125 MeV, are injected into the optical cavity. Changing the accelerating energy and/or undulator parameters, this system will cover the range from infrared to ultraviolet for the applications in the various fields.

Suppression of coherent synchrotron radiation in conducting boundaries

The intensity of coherent synchrotron radiation was measured in the presence of finite parallel plate metallic shields with a variable gap by using the Tohoku 300 MeV Linac. The results can be qualitatively explained by the theory of suppression effect obtained by Nodvick and Saxon.<<ETX>>

Spectrum of coherent synchrotron radiation

A spectrum of coherent synchrotron radiation was measured at wavelengths of from 0.16 to 3.5 mm. The experiment was carried out using the Tohoku 300-MeV linac, whose accelerating frequency was 2856 MHz. A bunch shape was estimated by Fourier analysis for this spectrum. This result agrees with that of simulation for the bunching process in the injector of the accelerator. The interference effects between radiation emitted by the successive bunches were observed by an interferometer. It was shown that every radiation had the same phase when it was emitted by a bunch.<<ETX>>