Coherent bremsstrahlung at the HERA collider

We consider a new type of radiation at colliders with short bunches—coherent bremsstrahlung (CBS) which is the radiation of the first bunch particles caused by the collective electromagnetic field of the second bunch. The number of CBS photons for a single collision isdN _λ ≈N ₀ dE _λ /E _λ > in the energy rangeE _λ ?E _c = 4γ ₁ ² ?c/l ₂. Hereγ ₁=E ₁/m ₁ c ²;l ₂ is the length of the opposing (second) bunch andN ₀ is proportional toN ₁ N ₂ ² whereN _j is thej-th bunch population. For the HERA colliderN ₀=14,E _c =73 eV in the case when photons are emitted by protons andN ₀=6·10⁷,E _c =24 keV—when photons are emitted by electrons. Unusual properties of such a coherent bremsstrahlung and the possibility to use CBS for fast beam steering and for luminosity optimization are discussed.