MOTUI1
ANL, Argonne, USA
Principles behind a free-electron laser (FEL) will be explained in terms of simple physics. Characteristics of several varieties of FEL devices–amplifier, oscillator, and harmonic generator–will be delineated. The high-performance frontier in short wavelength, time resolution, and coherence will be discussed. Wild speculation for the future will be entertained.
ANL, Argonne, USA
Fluctuations in highly bright, relativistic electron beam for free electron lasers (FELs) exhibit both collective as well as individual particle aspects[1]. If the collective part characterized by plasma oscillation dominate, then it might be feasible to suppress the shot noise[2]. To study these issues, we solve the 1-D coupled Poisson-Klimontovich equations by the Laplace transform technique. We find the density fluctuations to be a linear combination of the collective plasma oscillation and the random motion of Debye-screened dressed particles[3]. The relative magnitude ξ of the random to the collective part can be computed explicitly. For the LCLS case, we find that ξ is about unity for electron beams just prior to the λ = 1.5 Å FEL, and about 1% for the beam at 135 MeV at λ = 1 μm. The “position noise” (bunching factor) could be reduced to about ξ by a quarter of plasma oscillation. However, this leads to an increase in the “momentum noise”, which contributes significantly to the growth of the self-amplified spontaneous emission.
[1] D. Pines, D. Bohm, Phys. Rev.,85,338 (1952)
[2] A. Gover, E. Dyunin, Phys. Rev.Letters, 102,154801 (2009)
[3] S. Ichimaru, Basic Principles of Plasma Physics, The Benjamin/Cummins Pub. Co. (1973)