  We consider the radiation of particles of one bunch in the collective field
of the oncoming bunch, called coherent bremsstrahlung (CBS). The main
characteristics of CBS for LHC (in the Pb-Pb mode) and for RHIC are calculated.
At LHC about $3.9 10^8 dE_\gamma/E_\gamma$ photons per second are expected for
photon energies $E_\gamma \stackrel{<} {\sim} E_c= 93 $ eV. It seems that CBS
can be a potential tool for optimizing collisions and for measuring beam
parameters. The bunch length can be found from the critical energy of the CBS
spectrum; the transverse bunch size is related to the photon rate. A specific
dependence of photon rate on the impact parameter between the beams allows for
a fast control over the beam displacement.
