Performance of the accelerator driver of Jefferson Laboratory´s free-electron laser

The driver for Jefferson Lab´s kW-level infrared free-electron laser (FEL) is a superconducting, recirculating accelerator that recovers about 75% of the electron-beam power and converts it to radiofrequency power. In achieving first lasing, the accelerator operated “straight-ahead” to deliver 38 MeV, 1.1 mA cw current through the wiggler for lasing at wavelengths in the vicinity of 5 μm. Just prior to first lasing, measured rms beam properties at the wiggler were 7.5±1.5 mm-mr normalized transverse emittance, 26±7 keV-deg longitudinal emittance, and 0.4±0.1 ps bunch length which yielded a peak current of 60±15 A. The waste beam was then sent directly to a dump, bypassing the recirculation loop. Stable operation at up to 311 W cw was achieved in this mode. Commissioning the recirculation loop then proceeded. As of this Conference, the machine has recirculated cw average current up to 4 mA, and has lased cw with energy recovery up to 710 W