A linear integral-equation-based computer code for self-amplified spontaneous emission calculations of free-electron lasers

The linear integral-equation-based computer code “Roger Oleg Nikolai” (RON), which was recently developed at Argonne National Laboratory, was used to calculate the self-amplified spontaneous emission (SASE) performance of the free-electron laser (FEL) being built at Argonne. Signal growth calculations under different conditions were used to estimate tolerances of actual design parameters and to estimate optimal length of the break sections between undulator segments. Explicit calculation of the radiation field was added recently. The measured magnetic fields of five undulators were used to calculate the gain for the Argonne FEL. The result indicates that the real undulators for the Argonne FEL (the effect of magnetic field errors alone) will not significantly degrade the FEL performance. The capability to calculate the small-signal gain for an FEL-oscillator is also demonstrated.