Wednesday, March 21, 2007

What Is an Energy Recovery Linac (ERL)?

An Energy Recovery Linac (ERL) x-ray source is a candidate next-generation x-ray source technology now under active development. ERLs are made possible by recent advances in superconducting linear accelerators and in high-brightness electron sources. ERLs have the potential to generate synchrotron radiation with brightness about 1000 times greater than that of today's storage rings, resulting in highly coherent x-radiation. ERL's are particularly well suited for the production of very fast x-ray pulses to examine the dynamics of materials on extremely rapid time scales and for intense x-ray nanoprobe beams to study nanoscopic matter. While both ERLs and XFELS will be able to produce very fast x-ray pulses, the two sources are quite distinct in the timing of these pulses: ERLs are being designed to produce pulses times up to a billion times a second whereas XFELs produce bigger pulses but at a far lower rate per second.

Image 1. Electrons are released from the injector at the lower left, and are accelerated in a long linear superconducting accelerator (main linac). After emerging from this linac, the electrons pass through undulators that wiggle the electron beam and produce the x-rays in the usual way. Electrons are continuously injected, make one trip around the ring, and return to the main linac where their energy is recovered. The spent beam is directed to the dump. (Courtesy: Cornell University)

1 comment:

Anonymous said...

Georg Hoffstaetter, Cornell University
The Energy Recovery Linac as a New X-ray Source
Physics Division Colloquium - 23 Mar 2007

Research toward a new type of x-ray source will be presented. This source is very different compared to a storage ring, where electrons are recycled for many turns in order not to lose their energy. An energy recovery linac (ERL) rather recycles energy by leading electrons that have created x-rays to a decelerating section where their energy is used to accelerate a new beam of electrons. Each x-ray beamline is thus continuously served by a newly accelerated electron beam.

After a review of how existing light-source storage-rings produce x-ray beams, their state-of-the-art limits are pointed out. It is shown how an ERL could produce improved x-ray parameters by providing beams with reduced cross section, reduced energy spread, and reduced bunch length.

At Cornell University's Center for Accelerator Sciences and Education (CLASSE) work is under way to verify the principles on which these improvements rely. An electron source and a superconducting accelerating section is currently being built and effects that can degrade beam properties are being studied. An ERL is planned as an extension to the existing CESR storage ring by implementing a 5-GeV superconducting c.w. linac. This planned upgrade illustrates how other existing storage rings could be upgraded as ERL light sources with significantly improved beam qualities and with limited dark time for x-ray users.