The Making of a High-Average-Power Free-Electron Laser: Snatching a Holy Grail

Courtlandt L. Bohn, Fermilab (formerly Jefferson Lab)

Abstract

Jefferson Laboratory's kW-level infrared free-electron laser comprises a superconducting linear accelerator that powers itself by recovering energy from the post-lasing electron beam. In achieving first lasing, the accelerator operated "straight ahead" to deliver 38-MeV, 1.1-mA cw current for lasing near 5 µm. The waste beam was sent directly to a dump during stable operation at up to 311 W. Using a recirculation loop to send the electron beam back to the accelerator for energy recovery, the accelerator now produces cw average currents up to 5 mA while lasing cw at wavelengths between 3-6 µm. It has produced up to 1720 W continuous output power at 3.1 µm. The machine is now a users' facility supporting a full slate of user experiments. In this talk I will highlight top-level design considerations and the commissioning process that led to this performance capability. I will also highlight beam-physics experiments concerning coherent synchrotron radiation and multipass beam breakup, as well as the production of incoherent x-rays by Thomson scattering during lasing.