Improved High-Current Injector Design

"With the achievement of 2.1 kW CW I R operation and an upgrade to10 kW in progress, free-electron lasers (FEL) are now a serious option for high-power, military and commercial applications. As specifically identified in the recent "Department of DefenseLaser Master Plan", the key technology issue on the path to high-power FEL deployment is the demonstration of reliable, high-brightness, photocathode injector operation. A DC gun/superconducting accelerator combination provides the most promising and mostmature path to efficient, weapon-level electron beam power. One of the primary issues identified with this type of gun is beam quality degradation for operation at weapon system charge levels that approach 1 nC per bunch or higher. Longitudinal phasespace aberrations set in that can significantly reduce the lasing efficiency of the FEL. We are proposing to design a doubly resonant first accelerating cavity to both correct the development of this aberration and accelerate the electron beam for currentlevels that approach one ampere. The proposed design will represent a proof-of-principle demonstration. The discriminating attributes of FELs are their wide-band tunability, their implicit potential for very high-power operation and the intrinsicpicosecond pulse structure that promises superior performance for certain applications. Significant military FEL directed energy weapon (DEW), countermeasure and communication applications ex