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Figure 8
An electron bunch having peak current of order 300 Apk is switched into a transverse gradient undulator (TGU) in a bypass of a 2.2 km ring (left) to produce a 1.5 nm, 0.5 mJ self-amplified spontaneous emission (SASE) FEL pulse (Hettel et al., 2009BB22). The inherent electron energy spread and vertical lattice dispersion in the TGU produce an almost round electron beam with a linear energy distribution in the vertical plane that maintains lasing resonance at a single photon wavelength. Evolution of photon power along the TGU length, radiation spectral content, and single-mode coherent beam profile are shown on the right. The spent electron bunch is returned to the ring where its lasing-induced energy spread is damped before the bunch is ready for lasing again. Other damped bunches are switched into the bypass during this damping period, which is typically a few tens of milliseconds. Producing a high peak current bunch in the ring is challenging, potentially requiring a high-voltage (few hundred MV) high-frequency (∼1.5 GHz or more) RF system.

Journal logoJOURNAL OF
SYNCHROTRON
RADIATION
ISSN: 1600-5775
Volume 21| Part 5| August 2014| Pages 843-855
doi:10.1107/S1600577514011515
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