  On the basis of an energy-recovery linac, a terahertz (THz) source with
kilowatts average power is proposed in Shanghai, which will serve as an
effective tool in material and biological sciences. In this paper, the physical
design of two free electron laser (FEL) oscillators, in the frequency range of
2~10THz and 0.5~2THz respectively, are presented. By using three dimensional,
time-dependent numerical modeling of GENESIS in combination with paraxial
optical propagation code (OPC), the THz oscillator performances, the detuning
effects, and the tolerance requirements on the electron beam, the undulator
filed and the cavity alignment are given.
