S. Urasawa

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.

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>>

Coherent Smith‐Purcell radiation in the far‐infrared region from a short‐bunched electron beam

Coherent Smith‐Purcell radiation, emitted from short‐bunched electrons passing by a lamellar‐type grating of aluminum, has been observed in the millimeter wave region. The energy of the electrons is either 42 MeV when they are accelerated by an L‐band linear accelerator or 150 MeV accelerated by an S‐band one. The intensity of the radiation is proportional to the square of the beam current. The radiation is linearly polarized, and the electric vector of the radiation is in the plane defined by the observing point and the beam trajectory. The intensity decreases with the beam height, i.e. the distance of the beam from the surface of the grating, in accordance with the modified Bessel function of zeroth order.

Suppression and enhancement of coherent synchrotron radiation in the presence of conducting boundaries

The suppression effect of coherent synchrotron radiation due to conducting boundaries has been studied using the Tohoku University 300‐MeV electron linac. It has been experimentally observed that emission of coherent synchrotron radiation is not only suppressed but also enhanced with nearby metallic plates. The variation of the relative intensity of coherent synchrotron radiation with the gap between the metallic plates is well explained by the theory of Nodvick and Saxon. The emission of coherent synchrotron radiation in the long‐wavelength region is suppressed more than predicted by the theory, which indicates that there may be other effects suppressing the emission.

Coherent radiation at submillimeter and millimeter wavelengths

The paper describes the experimental results on coherent synchrotron radiation (SR), coherent Cherenkov radiation (CR) and coherent transition radiation (TR) at submillimeter and millimeter wavelengths. Coherent radiation intensities vs. He gas pressure are shown at /spl lambda/=500 nm and 4 mm. Angular distributions of coherent CR and/or coherent TR were obtained in vacuum and at atmospheric pressure. Coherent TR spectra at different emission lengths were obtained at /spl lambda/=0.2/spl sim/5 mm.<<ETX>>