SwissFEL ready for assembly
Researchers from PSI have spent the last four years developing key technologies for the X-ray laser SwissFEL and subjecting them to the acid test in the injector test facility. Now that the development programme has drawn to a close, the installation of the new large research facility is due to get underway in early 2015.
The X-ray free-electron laser SwissFEL will produce very short pulses of X-ray light with laser-like properties at a high intensity. This is done by generating electrons, which are then brought to a high energy level with the aid of a linear accelerator. After being accelerated the electrons are send on a slalom course using undulators, a special arrangement of magnets. While they zigzag, the electrons emit light, which intensifies itself strongly and culminates in the brilliant flash of X-ray light that is used for the experiments on SwissFEL.
High technological demands
Roughly 570 metres of the 740-metre-long facility are used to generate X-ray light in SwissFEL. The compact structure of the Paul Scherrer Institute´s new large research facility necessitated numerous technological refinements and new developments. Once completed, SwissFEL will be one of five X-ray free-electron lasers in the world. Compared to the other facilities, however, it will work with a considerably lower beam energy level.
In order to produce SwissFEL X-ray light at this low electron energy, an electron beam of extreme high quality is required.
It needs to be perfect from the beginning, explains Thomas Schietinger, head of the Accelerator Concepts Section at PSI. Consequently, a development programme was launched at PSI four years ago, which concentrated on the initial part of the facility that generates the electrons, gives them their first acceleration thrust and focuses them: the injector.
Tests under realistic conditions
In the injector test facility, feasibility studies were conducted and key technologies developed, tested and optimised. In doing so, the researchers ventured into unchartered technological territory:
We had to demonstrate that the electron beam required could actually be generated and characterised, stresses Marco Pedrozzi, head of the injector test facility.
Once this had been achieved, the PSI research team headed by Schietinger worked hard to optimise the beam quality and make sure that it could be sustained over the entire accelerator course. The electron beam was put to an initial acid test after the installation of an undulator prototype:
The results of operating the beam with an undulator lived up to our expectations – we managed to produce the first free-electron laser beam in Switzerland, says a delighted Schietinger.
The last few months in operation were devoted to testing the electron source that will generate the electrons in SwissFEL. It is to be moved to the SwissFEL building in mid-2015, where the two-year installation of the facility is due to get underway at the beginning of 2015. Pedrozzi reflects on a successful development programme:
Thanks to our tests under realistic conditions, we were able to make a key contribution to its successful realisation.
Text: Paul Scherrer Institute/Martina Gröschl