Contact: Ben Shepherd
Undulators are magnetic devices consisting of an array of alternating magnets. They are usually installed on the straight sections of storage ring based light sources. When an electron beam passes through an undulator, it moves in a ‘wiggle’ shaped trajectory, emitting an intense beam of light.
Most undulators installed on light sources use permanent magnets. A novel type of undulator using superconducting wires to generate the magnetic fields has been developed by the MaRS group in collaboration with engineers and scientists at the Rutherford Appleton Laboratory’s Technology Department. The eventual aim of this project is to construct and install a 2m long superconducting undulator at Diamond Light Source.
A superconducting undulator has several advantages over conventional undulator technology. It can reach higher fields and use shorter periods, meaning that it can produce extremely intense beams of light at very short wavelengths. However, the technology required to build such a device is far from straightforward. In order for the wire to become superconducting, the undulator must be cooled to a temperature of 4.2K (-269°C) using liquid helium. To further enhance the field, it is planned to operate the undulator at an even lower temperature of 1.8K (-271°C). The superconducting wires are wound around a steel former to concentrate the field. This steel structure also presents some engineering challenges. In order to provide the highest quality magnetic field, the steel poles must be machined to a flatness of less than 20µm (0.02mm). Similar tolerances apply to the pitch (the distance between the poles) and to the alignment between formers.
The team at RAL, led by Tim Hayler and Tom Bradshaw, have been working on a short prototype of this undulator, using four 30 cm long steel formers. The superconducting wire has been painstakingly wound around these formers in a helical pattern to produce the undulator’s alternating magnetic field. This undulator prototype will be measured at RAL and then brought to Daresbury in 2018. We plan to install it on CLARA with some photon diagnostics to measure the quality of the light beam produced. This will give valuable insights into any improvements in manufacturing we can apply to the next version of the undulator.