Short-Period RF Undulator for a SASE Nanometer Source

For future compact light sources for discovery science and medical diagnostics, it would be beneficial to reduce the energy of the electron beam constituting the source. For nanometer wavelength radiation, the radiation would be Self-Amplified Spontaneous Emission (SASE), originating when the beam undulates in a periodic transverse magnetic field. For a given radiation wavelength, reducing the undulator period allows a concomitant reduction in the beam energy. But practical limits prevent arbitrary reductions in the period for a static undulator. However, an electromagnetic undulator does not encounter those limits. This project is aimed at design that uses cavities energized with high-power 34-GHz radiation to create an undulator with a period less than 1 cm, with an undulator parameter of the order of unity, and with an aperture (or gap) greater than 2.25 mm. Cavities are to be devised that can support the strong electromagnetic fields needed for this application, and which lend themselves to cascading for realizing an undulator several meters in length. Commercial applications and other benefits: Present light sources that generate nanometer-scale radiation are large, expensive, and located at only a few national laboratories in the US. If such sources were made less expensive and smaller, by reduction in the energy of the electron beam needed through use of an undulator developed in this project, it could make it possible to install the sources at regional centers where they would be more widely available than at present. Medical and industrial uses for these nanometer light sources could generate an annual market of many millions of dollars that in turn would create a large demand for the new undulators.