A new high-brightness electron injector for free electron lasers driven by RF linacs

Abstract A free electron laser oscillator, driven by an RF linac, requires a train of electron bunches delivered to an undulator. The brightness requirement exceeds that from a conventional linac with rf bunchers. The demonstrated high brightness of laser-illuminated photoemitters indicates that the conventional buncher system might be eliminated entirely, thereby avoiding the usual large loss of brightness that occurs in bunchers. A photoemitter with a current density of about 200 A/cm 2 is placed on an end wall of an rf cavity to accelerate a 60 ps bunch of electrons to 1 MeV as rapidly as possible. Preliminary experimental work, simulation calculations, and discussions on emittance measurement techniques and positive ion motion in the rf gun are presented.