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XX International Linac Conference

MOB17 (Poster)

Presenter: Nicholas Sereno (ANL)
Status: Complete
FullText: ps.gz or pdf
Eprint: physics/0008116

Use of Coherent Transition Radiation to Set Up the APS RF Thermionic Gun to Produce High-Brightness Beams for SASE FEL Experiments*

N. S. Sereno, M. Borland, A. H. Lumpkin (ANL)

We describe use of the Advanced Photon Source (APS) rf thermionic gun, alpha magnet beamline, and linac[1] to produce a stable high-brightness beam in excess of 100 amperes peak current with normalized emittance of 10 pi mm-mrad. To obtain peak currents greater than 100 amperes, the rf gun system must be tuned to produce a FWHM bunch length on the order of 350 fs. Bunch lengths this short are measured using coherent transition radiation (CTR) produced when the rf gun beam, accelerated to 40 MeV, strikes a metal foil. The CTR is detected using a Golay detector attached to one arm of a Michelson interferometer. The alpha magnet current and gun rf phase are adjusted so as to maximize the CTR signal at the Golay detector, which corresponds to the minimum bunch length. The interferometer is used to measure the autocorrelation of the CTR radiation. The minimum phase approximation[2] is used to derive the bunch profile from the autocorrelation. The high-brightness beam is accelerated to 217 MeV and used to produce SASE in five APS undulators installed in the Low- Energy Undulator Test Line (LEUTL) experiment hall[3]. Initial optical measurements showed a gain length of 1.3 m at 530 nm.
[1] J. Lewellen et al., 'Operation of the APS RF Gun,' Proceedings of the 1998 Linac Conference, ANL-98/28, 863-865 (1999).
[2] R. Lai and J. Sievers, 'Determination of Bunch Asymmetry from Coherent Radiation in the Frequency Domain', AIP Vol. 367, 312-326 (1996).
[3] S.V. Milton et al., 'Observation of Self-Amplified Spontaneous Emission and Exponential Growth at 530 nm,' (submitted to Phys. Rev. Lett.).
* Work supported by U. S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

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