The amplitude of Parametric X-ray radiation emitted coherently by a bunch of
electrons crossing a crystal (CPXR) is calculated. When the bunch density is
modulated with a longitudinal period close to the X-ray wavelenght,
constructive many-electron interferences enhance the intensity by Nb *
|F(K)|^2, where Nb is the number of electrons in the bunch, F(K) the bunch form
factor and K a specified wave vector. CPXR can be used to test the
microbunching in a X-ray free-electron laser.Comment: 6 pages, no figure. Presented at NATO Advanced Research Workshop on
Electron-Photon Interaction in Dense Media (Nor Hamberd, Armenia, 25-29 June,
2001
