Development of a Superconducting Transverse-Gradient Undulator for Laser-Wakefield Accelerators

Relativistic electrons with small energy spread propagating through undulators produce monochromatic radiation with high spectral intensity. The working principle of undulators requires a small energy spread of the electron beam in the order of
$\Delta E/E \sim 0.1\%$
. Laser-wakefield accelerators can produce electron bunches with an energy of several 100 MeV within a few millimeters acceleration length, but with a relatively large energy spread
$(\Delta E/E \sim 1{-}10\%)$
. In order to produce monochromatic undulator radiation with these electrons, a novel scheme involving transverse-gradient superconducting undulators was proposed in an earlier work. This paper reports on the design-optimization and construction of an iron-free cylindrical superconducting undulator tailored to the particular beam properties of the laser-wakefield electron accelerator at the University of Jena, Germany.