High current RF accelerator for FEL applications

The feasibility of basing free electron lasers in space depends upon reducing the size and weight of all system components to manageable levels. Two of the largest and most complex subsystems in any FEL concept are the accelerator and wiggler. Improvements in these two subsystems can provide a very high payoff. Only two types of accelerators hold promise for high power FELs: the induction linac and the rf accelerator. Both types can produce the high quality (i.e., high brightness and monoenergetic), high voltage (of order 100 to 200 MeV) electron beams needed to drive the FEL wigglers. Of these two, the induction linac concepts suffer size disadvantages because they are designed with relatively low accelerating field, real estate gradients and often use very heavy magnetic materials in acceleration cavities. Their advantage over most rf accelerator concepts is that they produce higher currents. These higher currents (of order a few kiloamps) can simplify the FEL wiggler subsystem by allowing it to operate as a single pass amplifier. At the lower currents typical of existing rf accelerator concepts, the wiggler must be configured as a master oscillator that requires a large and complex ring resonator and either grazing incidence optics or gas lenses. 1 ref., 4 figs