Source challenges resulting of the first applications of a UV storage ring FEL on Super-ACO
- CEA/DSM/SPAM, Gif-sur-Yvette (France)
Since 1992, significant progresses were achieved on the Super-ACO (S-ACO) storage ring Free Electron Laser (FEL) in the UV. The operation at the nominal energy 800 MeV has several consequences: higher average power in the UV (25 mW at 60 mA and more recently 100 mW at 100 mA available for the users), 10 hours of lasing for the same injection of positrons, providing enough time for performing an user experiment, compatibility with the users of synchrotron radiation (SR) in the temporal structure mode for 120 mA with the possibility of closing the four insertion devices of S-ACO. The main difficulties to extend the FEL optical performances come from the small gain (2%), limiting a rapid extention of the spectral range (either in the laser mode or by coherent harmonic generation from the FEL itself in the undulator) or linewidth narrowing. The installation of a 500 MHz harmonic cavity for bunch length reduction and gain increase is under consideration{hor_ellipsis} The stability of the FEL temporal and spectral was systematically followed versus time, for various scales (from ns to half an hour) with different detectors. The stability of the laser source has been significantly improved with a longitudinal feedback system allowing the jitter of the 25 ps RMS laser micropulse to be reduced from 150-200 ps down to 10-20 ps. the intensity fluctuations to be damped down 1% and the spectral drift to be smaller than the resolution of the scanning Fabry-Perot (0.01{angstrom}) at perfect synchronism. The laser can work during more than 3 consecutive hours without readjustments. In addition, according to the ring current, the positron beam is submitted to coherent modes of synchrotron oscillations. Right now, a Pedersen type longitudinal feedback damps the dipolar modes of such oscillation. The quadrupolar modes in the 120-60 mA range leading to a rather unstable FEL are on the way to be damped with an additional feedback.
- Research Organization:
- Brookhaven National Lab., Upton, NY (United States)
- OSTI ID:
- 238716
- Report Number(s):
- BNL--61982-Absts.; CONF-9508156--Absts.; ON: DE96002729
- Country of Publication:
- United States
- Language:
- English
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