  Circularly polarized colliding laser pulses can create abundant
electron-positron pair plasma [A. R. Bell and J. G. Kirk, Phys. Rev. Lett. 101,
200403 (2008)], which scattering the incoming electromagnetic waves can prevent
them from reaching the critical field of Quantum Electrodynamics causing vacuum
breakdown and polarization. It is shown that the effects of radiation friction
and the electron-positron avalanche development depend on the electromagnetic
wave polarization. For circularly polarized colliding pulses, which force the
electrons to move in circles, these effects dominate not only the particle
motion but also the evolution of the pulses. While for linearly polarized
pulses, where the electrons (positrons) oscillate along the electric field,
these effects are not as strong. There is an apparent analogy of these cases
with circular and linear electron accelerators with the corresponding
constraining and reduced roles of synchrotron radiation losses.
