1. G. Dattoli, P.L. Ottaviani, A. Segreto, A. Torre and H. Altobelli, J. Appl. Phys., to be published.
2. G. Dattoli, L. Giannessi, P.L. Ottaviani and A. Segreto, Phys. Plasmas, to be published.
3. Storage ring operation of the free-electron laser: The oscillator