6 v 1 2 6 M ay 1 99 8 Coherent bremsstrahlung at the BEPC collider

Coherent bremsstrahlung (CBS) is a specified type of radiation at colliders with short bunches. In the present paper we calculate the main characteristics of CBS for the BEPC collider. At this collider dN γ ∼ 3 · 10 8 dE γ /E γ photons of CBS will be emitted for a single collision of the beams in the energy range E γ < ∼ 240 eV. It seems that CBS can be a potential tool for optimizing collisions and for measuring beam parameters. Indeed, the bunch length σ z can be found from the CBS spectrum because critical energy E c ∝ 1/σ z ; the horizontal transverse bunch size σ x is related to dN γ ∝ 1/σ 2 x. Besides, CBS may be very useful for a fast control over an impact parameter R between the colliding bunch axes because a dependence of dN γ on R has a very specific behavior. It seems quite interesting to investigate this type of radiation at the BEPC collider (for example, in the range of a visible light with the rate about 3 · 10 14 photons per second) and to apply it for the fast beam control. 1 Three types of radiation at colliders Let us speak, for definiteness, about emission by electrons moving through a positron bunch. If the photon energy is large enough, one deals with the ordinary (incoherent) bremsstrahlung. If the photon energy becomes sufficiently small, the radiation is determined by the interaction of the electron with the collective electromagnetic field of the positron bunch. It is known (see, e.g. §77 in Ref. [1]) that the properties of this coherent radiation are 1