Coherence and linewidth studies of a 4 nm high power FEL

Abstract

Recently the SSRL/SLAC and its collaborators elsewhere have considered[1] the merits of a 2 to 4-nm high power FEL utilizing the SLAC linac electron beam. The FEL would be a single pass amplifier excited by spontaneous emission rather than an oscillator, in order to eliminate the need for a soft X-ray resonant cavity. We have used GINGER, a multifrequency 2D FEL simulation code, to study the expected linewidth and coherence properties of the FEL, in both the exponential and saturated gain regimes. We present results concerning the effective shot noise input power and mode shape, the expected sub-percent output line widths, photon flux, and the field temporal and spatial correlation functions. We also discuss the effects of tapering the wiggler upon the output power and line width.

Shot noise startup of the 6 nm SASE FEL at the TESLA test facility

“…GINGER can also treat any time dependent beam parameter variation over the electron/radiation pulses, like arbitrary beam current or energy distributions, and the initial shot noise over the electron phases. SASE startup is modeled adding random fluctuations to the particles longitudinal and transverse coordinates [7].…”

FEL Simulations for the LCLS

“…The analysis of startup from noise, saturation, as well as the temporal and spectral structure of the radiation pulse for the LCLS design uses the 2D, time-dependent simulation code GINGER [3,4], which models the interaction of the 3D motion of the electron beam with an axisymmetric, multi-frequency radiation field. SASE startup from shot noise is modeled by adding random fluctuations to the macro-particles' longitudinal and transverse coordinates [5]. Segment separations or lumped focusing are not implemented in GINGER.…”

Critical review of high-gain X-ray FEL experiments

“…The measurement was preliminary but indicated an effective input noise larger than that estimated from the theory [36]. A recent experiment at 47 microns may also have detected an input noise larger than the theoretical prediction Anticipating the success of these experiments, SLAC and DESY are currently carrying out detailed design reports for their x-ray SASE facilities.…”