Design, measurement and correction of a pair of novel focusing undulators for the ALPHA-X project

ALPHA-X is a UK collaboration to develop and build a prototype laser-plasma accelerator. The ALPHA-X beam line generates an electron bunch with energy 0.1–1 GeV; this is injected into a pair of permanent magnet undulators to generate a short pulse of radiation. The design of the undulators is detailed in this paper.The undulators have a requirement to focus the beam along their length. Several focusing schemes were analysed. The scheme used involved magnet blocks with a 5×1 mm slot cut into the top to provide a sextupole-type field.The undulators were built and tested at STFC's Daresbury Laboratory. Some block swapping was carried out for each one to reduce the overall field integrals and optimise the beam transport. The first field integral was reduced using this technique to less than 0.1 T mm for both undulators.