Energy Recovered Light Source Technology at TJNAF

Energy-recovered linac/TJNAF Free Electron Laser
Developed at:
Thomas Jefferson National Accelerator Facility, Brookhaven National Laboratory
Developed in:
Result of NP research:
Application currently being supported by:
DOE NP, Defense Programs, U.S. Navy, U.S. Air Force
Impact/benefit to spin-off field:
Directed energy and materials processing applications; new technology for accelerators for basic energy sciences, nuclear and particle physics and defense applications

The Department of Energy's Jefferson Lab is the site of the world's most powerful tunable laser: the Jefferson Lab Free-Electron Laser. The FEL became operational in 1998 and has produced light tunable from the far-infrared (Terahertz light), through the infrared, visible and ultraviolet wavelengths of light at levels several orders of magnitude more powerful than any other tunable light source. The FEL is capable of producing an unprecedented 14.2 kW of infrared laser light at 1.6 microns. The FEL is built on the unique superconducting radiofrequency technology developed at Jefferson Lab for DOE's Nuclear Physics program. In the FEL, electrons are whipped up to high energies by an SRF linear accelerator. A wiggler, a device developed by DOE and DOD during the 1980s for powerful x-ray sources, produces magnetic fields to oscillate or “wiggle” the electrons, forcing them to release energy in the form of photons. As in a conventional laser, the photons bounce between two mirrors and are emitted as laser light. SRF technology allows high average-power electron beams to be produced and operated in a cost-effective manner. In the FEL, it allows the laser to stay on 100 percent of the time instead of only one or two percent. Cost savings are compounded by the design of the FEL's unique energy-recovering linear accelerator. Once electrons have exited the wiggler, they are steered back into the machine's linear accelerator, allowing the machine to recover more than 90 percent of the energy that is not converted to useful light in a single pass. The strength of an energy-recovered linear accelerator is the economic feasibility of using the beam “only once” while not wasting its power in a dump.

The energy-recovered FEL has seen wide application in the fields of medicine, materials science, photochemistry and biophysics. This pioneering demonstration of SRF energy-recovery technology is the basis for an entire new class of devices that are currently being designed for basic energy sciences, nuclear and particle physics and defense applications. The Free-Electron Laser program is supported in part by the Department of Defense’s Office of Naval Research, the Naval Sea Systems Command, the Air Force Research Laboratory and the Joint Technology Office; and by the Commonwealth of Virginia.

Image: harmonic light is produced in the visible when the FEL lases in the infrared. Here the colors are dispersed in an image of the output.