Flashes of X-ray laser light

A straight line, not a ring

Unlike the Swiss Light Source, SwissFEL is straight. The facility is about 740 metres long and has four parts: an injector with an electron source, a linear accelerator, a series of undulators and the experimental stations.

It lies in the forest on the Würenlingen side of the river Aare, next to the rest of PSI. The injector, the accelerator tunnel and the undulator hall are built underground on a gravel base, with walls thick enough for radiation protection; power supplies and control equipment sit in five technical buildings on top of the tunnel.

How the flashes are made

A flash of laser light knocks electrons out of a metal plate. The linear accelerator then gives them an energy equivalent to crossing a voltage of 6 billion volts. The electrons pass through 12 undulators, each with 1,060 magnets, over a total of 60 metres. The magnets force them onto a wavy path, and the X-rays they emit build up in an avalanche-like amplification.

The result is a flash lasting between 1 and 60 femtoseconds. A femtosecond is a millionth of a billionth of a second.

Films of chemistry

Because the flashes are so short, researchers can take snapshots of the intermediate steps of a chemical reaction: a reaction is started with a laser and then imaged at different moments, frame by frame. PSI also names the structure of large biological molecules, which matters for new medicines, and the link between electronic and atomic structure in materials as uses of SwissFEL.

Aramis and Athos

The SwissFEL site was approved in 2011, the foundation stone was laid in 2013 and the facility was inaugurated in 2016. The experimental halls serve two beamlines, Aramis and Athos, and have room for up to six. Aramis, the first, began regular operation in January 2019.