Comparison of the Livermore microwave FEL results at ELF with 2D numerical simulation
The experimental results of the ELF microwave free-electron laser experiment are compared with 2D numerical simulations using the LLNL code FRED. The data comprises (1) microwave power vs. wiggler magnetic field at fixed wiggler length, (2) microwave power vs. wiggler length at fixed wiggler field, and (3) relative power in the two waveguide modes that couple strongly to the electrons, vs. wiggler length. The code evolves the electrons' energies and ponderomotive phases according to the averaged single-particle equations derived by Kroll, Morton, and Rosenbluth, and the fields according to the paraxial wave equation with the source term as derived by Colson. The particle motion is fully three-dimensional. The field solver is two-dimensional, but because only the lowest mode is excited in the short waveguide dimension, the code is accurately three-dimensional for microwave simulations. Longitudinal space-charge forces reduce the gain and increase the synchrotron period of the electrons (after saturation of the amplifier) by roughly 20%. Space-charge forces have been included in the code approximately (so that the running time of the code is not significantly increased), and bring experiment and theory into excellent agreement. The approximation used to add space-charge forces is described. 12 refs., 5 figs.
- Research Organization:
- Lawrence Livermore National Lab., CA (USA)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6046368
- Report Number(s):
- UCRL-93457; CONF-850956-22; ON: DE86006534
- Resource Relation:
- Conference: 7. international free-electron laser conference, Tahoe City, CA, USA, 8 Sep 1985
- Country of Publication:
- United States
- Language:
- English
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