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Design Overview of a Highly Stable Infrared Free Electron Laser at LBL


An infrared free electron laser (IRFEL) is being designed for the Chemical Dynamics Research Laboratory (CDRL) at LBL. The FEL is based on a 50 MeV rf linac operating in synchronization to the Advanced Light Source (ALS), and will produce intense (100 micro Joule per micropulse), narrow bandwidth (narrower than 0.1%) radiation between 3 and 50 micrometers. In the design, we pay particular attention to the FEL stability issues and require that the fluctuations in electron beam energy and in timing be less than 0.05% and 0.1 picosec, respectively. The FEL spectrum can then be stabilized to about 0.001, or if grating is used, 0.0001. We discuss various sources of fluctuations in the gun, the bunchers and the accelerator sections, as well as the feedback and feedforward schemes to reduce these fluctuations. The accelerator structure is chosen to be the side-coupled, standing-wave type for easier control. The beam transport is made isochronous to avoid the coupling between the energy and timing fluctuations.

K.J. Kim, M. Berz, S. Chattopadhyay, C. Kim, J. Edighofer, R. Gough, C. Kim, A.H. Kung, W. Stein, M. Xie, Nuclear Instruments and Methods A304 (1991) 233-237


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