The best accelerator in the world.

PETRA IV will be built according to an innovative design which will allow us to produce X-rays that are more than 100 times more focused than those generated by PETRA III.

The main components of the accelerator – the magnets that keep the electrons in the storage ring travelling along their circular path – are entirely new. “We are installing significantly more magnets in PETRA IV than in its predecessor, more than 4000 in total,” explains Bartolini. “They will guide and focuss the electrons in the ring in a much tighter way compared to PETRA III.” A positive effect of this is that the electron bunches will be more tightly bundled, thus emitting much narrower, high-intensity X-rays – which makes it possible to image and analyse a wide variety of materials and samples with far greater precision than before.

“Many magnets will be using permanent magnetic material,” Bartolini announces. “They allow a more compact design and consume less electrical power than an equivalent machine that uses electromagnets.” In addition to the 2.3-kilometre-long PETRA ring itself, the pre-accelerators and the transfer lines will also have to be entirely rebuilt.

Constructing the metal supports on which all the machine components will be mounted in groups, poses yet another challenge. The supports take the shape of five-metre-long blocks, which are to be completely fitted with the magnets and vacuum chambers before installation and then inserted into the ring as a whole. “The supports need to be as light as possible and at the same time extremely stable,” Bartolini explains. “Because of this, a lot of effort is going into their desing, optimisation and construction.”

Furthermore, the experts want to design the accelerator such that the electron bunches can orbit stably inside the ring over very different time scales from milliseconds to many hours at a time, without being disturbed by ground vibrations or other type of perturbations. “We are developing a control and feedback system to keep the electron and the photon beams precisely in position at all times,” reports the Machine project leader. “In all these technical challenges we are having to push the envelope of the current technology.”

And how is the design work coming along at the moment? “In terms of the machine itself, we are well on our way,” Bartolini replies. “The current design is in place and has not changed significantly for many months. We believe the project is feasible and will deliver the desired properties.” To put it another way: the basic plans have been finalised and DESY’s experts are essentially ready to go. Once they receive the go-ahead, they will be able to quickly get started on building this innovative accelerator.