SIMULATIONS OF APEX ACCELERATOR PERFORMANCE IN THE NEW NONTHERMALIZEDPHOTOINJECTOR REGIME

The Los Alamos accelerator FEL facility APEX is the first photoinjecto r-driven machine operating in the high-charge (greater than one nC), l ow-emittance (normalized rms emittances less than 5pi mm mrad) regime. Because the electron beam is accelerated quickly and does not have a chance to thermalize, surprising effects are seen. We will analyze and provide numerical examples showing the emittance degradation caused b y transverse wakefields and transverse quadrupole rotations. We will a lso show the formation of a virtual cathode as the injection phase is brought closer to the rf zero-crossing. FEL interaction simulations wi ll be included to differentiate emittance growth mechanisms that degra de FEL performance from those that are transparent to the lasing.