Use of Jefferson Lab´s high average power FEL as a Thomson backscatter X-ray source

Recently, workers from Berkeley have measured Thomson forward scattered X-rays at the ALS injector. The average power of their device was limited by, among other things, the repetition rate of the high power laser. In order to achieve high average power, it is natural to investigate the possibility of backscatter from the recirculating optical pulses in Jefferson Lab´s CW IRFEL, now under construction. Photon brightnesses of order 10⁷ photons/(sec mm² mrad²) will be produced at this facility, with a spectrum extending up to 7 keV in energy, in the present operating mode. A near-term upgrade to 75 MeV yields about 30 keV photons with similar brightness. In the longer term, the UV upgrade of our device could potentially produce 4 MeV photons with substantially higher brightness. Scaling laws for such configurations are given and these three cases are presented in detail