Energy recovery linac (ERL) coherent hard x-ray sources

Energy recovery linacs (ERLs) have the potential to be superb coherent hard x-ray sources. ERLs are described with reference to a 5 GeV ERL design being studied at Cornell University. The properties of this ERL, and the x-ray beams that may be produced, are described and spectral curves are calculated and compared to other existing and future x-ray sources. It is shown that ERL and x-ray free electron laser (X-FEL) sources are complementary in terms of the experiments they may optimally serve. ERLs will be especially advantageous in a variety of coherent and nanobeam experiments where the sample must be repetitively probed and in cases where the samples are unique and the requisite scattering information cannot be obtained with a single X-FEL pulse. ERL strengths are elaborated relating to the very high coherent flux, inherently round beams, flexibility and quasi-continuous time structure of the sources. Examples are given where these x-ray characteristics will facilitate advancement of important 'big challenge' areas of science.