Emittance, Brightness, Free-Electron Laser Beam Quality, and the Scaled Thermal Velocity
We discuss the role of emittance, brightness, and other factors affecting the quality of beams in the free electron laser. Since the key parameters in the dynamics of the free electron laser interaction depend on the beam density and axial energy spread of the beam, the ratio of the current density to the relative axial energy spread is taken as a figure of merit for comparing the quality of electron beam sources as potential drivers of free electron lasers. The scaled thermal velocity is introduced as a parameter in estimating the effect of thermal spread in a high gain free electron laser. We find that the effective thermal spread regime can be made small near the cyclotron resonance in field immersed free electron lasers, and the unusual possibility that the efficiency of the fastest growing mode with warm beams can be higher than cold beams. A detailed dispersion relation for the free electron laser interaction where the beam energy distribution is determined by pitch angle scattering and the total beam energy is conserved is presented. Numerical solutions for the growth rate and efficiency are calculated which show a shift to lower phase velocity as a function of momentum spread and an increase in efficiency of the fastest growing mode.
KeywordsElectron Beam Beam Quality Thermal Velocity Energy Spread Free Electron Laser
Unable to display preview. Download preview PDF.
- Freund, H. P., and Ganguly, A. K., 1986, Phys. Rev, (to be published)Google Scholar
- Lau, Y. Y., 1985, “Effects of Cathode Surface Roughness on the Quality of Electron Beams,” Bull. Am. Phys. Soc.30, 1583. Also, J. Appl. Phys. (Jan 1987 issue)Google Scholar
- Lawson, J. D., 1977, The Physics of charged Particle Beams. (Oxford University Press, Oxford, UK) Chap. 4Google Scholar
- Lee, E. P. and Cooper, R. K., 1976, Particle Acc., 7:83Google Scholar
- Neil, V. K., 1979, SRI Tech. Rep. JSR-79–10Google Scholar
- Roberson, C. W., Pasour, J. A., Mako, F., Lucey, R. F. and Sprangle, P., 1983, Chapter 7, Infrared and Millimeter Waves 10, 361Google Scholar
- Sprangle, P., Tang, C. M. and Roberson, C. W., Nucl. Instr. and Methods, 1985, Phys. ResearchA239, 1; and Laser Handbook, Vol. 4, eds. M. Stitch and M. S. Bass, North Holland, Amsterdam (to be published)Google Scholar
- Yariv, A., 1976 Introduction to Optical Electronics (Holt, Rinehart, and Winston) Chap. 3Google Scholar