Spectrum and polarization of coherent and incoherent radiation and the LPM effect in oriented single crystal

The spectrum and the circular polarization of radiation from longitudinally polarized high-energy electrons in an oriented single crystal are considered using the method which permits inseparable consideration of both the coherent and the incoherent mechanisms of photon emission. The spectral and polarization properties of radiation are obtained and analyzed. It is found that in some part of the spectral distribution the influence of multiple scattering (the Landau-Pomeranchuk-Migdal (LPM) effect) attains the order of 7%. The same is true for the influence of multiple scattering on the polarization part of the radiation intensity. The degree of the circular polarization of the total intensity of radiation is found. It is shown that the influence of multiple scattering on the photon polarization is similar to the influence of the LPM effect on the total intensity of radiation: it appears only for relatively low energies of radiating electron and has the order of 1%, while at higher energies the crystal field action excludes the LPM effect.