Strong focusing system of FELI 6-MeV electron injector used for ultraviolet range FEL oscillation

First lasings of free electron laser (FEL) at ultraviolet range were achieved by using an electron linac with a thermionic gun. The gun is driven by a 22.3125 MHz, 0.5 ns wide, 150 V grid pulser. A short-bunching and strong-focusing system of the injector and a stable 24 μs RF system allow lasing at 278 nm in spite of a small signal gain of 6%. The maximum focusing field is 0.11–0.12 T near the inlet of the buncher. The axial field distribution gives severe effect on lasing.