• H. Freund
  SAIC, McLean

Funding: Work supported by ONR, NAVSEA, and the JTO

Time-dependent FEL simulations use a variety of techniques. Most simulations use a slowly varying envelope approximation (SVEA). One such technique assumes that the envelope varies only in z combined with a field representation as an ensemble of discrete harmonics, which is equivalent to a time-dependent simulation [1] but is computationally prohibitive. A second technique uses an SVEA in both in z and t [2]. The particles and fields are advanced in z using the same process as in steady-state simulations and then the time derivative describing slippage is applied. This is used in wiggler-averaged codes such as GINGER [3] and GENESIS [4]. We describe the inclusion of this technique in the non-wiggler-averaged code MEDUSA [5], which is applied to amplifiers and oscillators. MEDUSA differs from GINGER and GENESIS also in the way the field is treated. GINGER and GENESIS use a field solver and must explicitly propagate the field outside the wiggler oscillators. This is computationally intensive. MEDUSA uses a Gaussian mode ensemble; hence, there is no need to propagate the fields outside the wiggler, and MEDUSA is able to simulate FEL oscillators in 3-D using relatively modest computational resources.

[1] N. Piovella, Phys. Plasmas 6, 3358 (1999). [2] R. Bonifacio et al., Phys. Rev. A 40, 4467 (1989). [3] W. Fawley, LBID-2141, CBP Tech Note-104, UC-414, 1995. [4] S. Reiche, NIMA 429, 243 (1999). [5] H.P. Freund et al., IEEE JQE 36, 275 (2000).