Unipolar Cherenkov and Diffraction Radiation of Relativistic Electrons

Abstract: For ordinary (bipolar) radiation, the integral of the electric-field strength in time is zero. The possibility of generating unipolar radiation was theoretically considered in (E.G. Bessonov. Preprint no. 76, Lebedev Physical Institute, Academy of Sciences of the Soviet Union, Moscow, 1990) for the first time. In this work, unipolar radiation is defined as radiation for which the integral of the electric-field strength in time differs significantly from zero. Later, a number of theoretical articles were devoted to this problem, mainly as applied to synchrotron radiation. However, there are still no experimental studies of this phenomenon. This paper presents the results of an experimental observation of unipolar Cherenkov and diffraction radiation generated by relativistic electrons in the millimeter wavelength range. For this, a detector was developed that is sensitive to the selected direction of electric-field strength. We observed coherent Cherenkov radiation and the backward diffraction radiation of a beam of relativistic electrons when electrons move close to targets. The effect of partial unipolarity is registered for Cherenkov radiation, and almost complete unipolarity is observed for backward diffraction radiation.