PHOTON EMISSION BY ULTRA-RELATIVISTIC POSITRONS IN CRYSTALLINE UNDULATORS

摘要

We discuss a mechanism, initially proposed in [1, 2], for the generation of high-energy photons by means of planar channeling of ultra -relativistic positrons through a periodically bent crystal. In this system there appears, in addition to the well-known channeling radiation, an undulator type radiation due to the periodic motion of the channeling positrons which follow the bending of the crystallographic planes. The intensity and the characteristic frequencies of this undulator radiation can be easily varied by changing the positrons energy and the parameters of the crystal bending. The mechanism of the photon emission by means of the crystalline undulator is illustrated in Fig. 1. It is important to stress that we consider the case when the amplitude a of the bending is much larger than the interplanar spacing d (～10~(-8) cm) of the crystal (a ～ 10 d), and, simultaneously, is much less than the period λ of the bending (a ～ 10~(-5) ... 10~(-4) λ).