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Free-electron laser bunch lengthening on the ACO storage ring

Thesis/Dissertation ·
OSTI ID:5418868
Operation of a free-electron laser as part of a storage ring (SRFEL) will cause an increase in the nominal energy spread of the electron bunch in the ring if the optical phase of the electrons is uncorrelated from pass to pass. This increase in energy spread results in an enlargement of the bunch length. The increased bunch length and energy spread cause a reduction in gain and can lead to the saturation of the SRFEL for low gain systems. This FEL-induced bunch lengthening has been measured for the first time on the ACO storage ring at the LURE laboratory, Orsay, France using the NOEL permanent-magnet undulator and optical klystron. In order to measure this induced bunch lengthening from the FEL interaction, a frequency-domain technique has been developed which measures induced bunch-length changes to 1 part in 10/sup 3/ and absolute bunch lengths to a precision of 1% as established by data taken on stored electron beams. Comparisons are made with existent theory for the idealized SRFEL and with numerical simulation. At low current these results show good agreement with the theory in both amplitude of bunch lengthening and the functional dependence on the various machine parameters. At higher current, coherent modes are present in the electron bunch. Strong correlations between the coherent mode thresholds and anomalous behavior of the electron bunch in the presence of the laser have been observed. Bunch shortening oscillatory behavior, and multiple time constant phenomena were observed.
Research Organization:
Stanford Univ., CA (USA)
OSTI ID:
5418868
Country of Publication:
United States
Language:
English