• S. Krishnagopal, S.A. Samant
  BARC, Mumbai

Mode stability can restrict the tuning range of FEL oscillators. We investigate the stability of FEL oscillators as a function of wavelength as well as size of the coupling hole. We show that concentric configurations are preferred to confocal ones. We study mode-stability using multi-particle simulations, for both, symmetric as well as asymmetric modes.