Developing an improved pulsed mode operation for Duke storage ring based FEL
The Duke FEL and High Intensity Gamma-ray Source (HIGS) facility is operated with an e-beam from 0.24 to 1.2 GeV and a photon beam from 190 to 1060 nm. Currently, the energy range of the gamma-ray beam is from 1 MeV to about 100 MeV, with the maximum total gamma-ray flux about 3E10 gammas per second around 10 MeV. The FEL is typically operated in quasi-CW mode. Some HIGS user experiments can benefit tremendously from a pulsed mode of FEL operation. For that purpose, a fast steering magnet was developed years ago [1] to modulate the FEL gain. This allows a build-up of a high peak power FEL pulse from a well-damped electron beam. However, the use of this gain modulator at low e-beam energies can dramatically limit e-beam current due to beam instability and poor injection. It also suffers from the problem of a significantly reduced ebeam lifetime. To overcome these shortcomings, we developed and successfully tested an RF frequency modulation technique to pulse the FEL beam. In this paper, we will describe this development, and report our preliminary results of this improved pulsed FEL operation.
