Japan and Europe make further progress with LIPAc

The Linear IFMIF Prototype Accelerator (LIPAc) is entering a new chapter towards achieving a high-power continuous wave. Developed by Europe and Japan as part of the Broader Approach agreement, LIPAc aims to validate the design of an ion accelerator to test materials for future fusion machines like DEMO.

This June, the teams from Fusion for Energy (F4E) and National Institutes for Quantum Science and Technology (QST) gathered in-person and online in Rokkasho, Japan, to celebrate the wrap-up of another successful round of operations. But many were already eyeing the next phase with excitement, as the accelerator will break new ground by reaching its final configuration.

In a nutshell, LIPAc consists of a chain of high-technology sections that generate, shape and accelerate a deuteron beam. You can think of it as a 36-m gun firing particles on a beam dump. In future material testing facilities like IFMIF-DONES, the accelerated particles will hit on a lithium target, generating a shower of neutrons, equivalent to the irradiation that materials inside a fusion reactor must withstand. But, to create these conditions, experts must demonstrate with the LIPAc prototype that such an accelerator can meet the requirements in terms of energy, current, duty cycle and duration.

Naturally, this could not be achieved in a one-shot experiment. Europe and Japan chose a stagewise approach, adding sections to the beam line as they commission the accelerator and validate the technologies. From the first low-intensity bursts seven years ago, LIPAc is now capable of producing higher energy beam with longer pulses. During its latter phase, it operated at a beam current of around 118mA, producing an energy of 5 MeV at 8.75% of duty cycle. This was reached thanks to components like the Radio Frequency Quadrupole (RFQ), with an unprecedented length of 9.8 m.

Now, the accelerator will hold fire for nearly two years, as the teams prepare it for its ultimate configuration. Experts are already working to assemble and integrate the Superconducting Radio Frequency (SRF) linear accelerator, the component that will raise the energy of the deuteron beam up to 9 MeV.

With these developments, LIPAc is venturing into unchartered territory. “We are moving to current levels and duty cycles that have not been reached yet anywhere in the world,” claims Yann Carin, Project Leader of IFMIF/EVEDA. However, despite the degree of risk, the know-how gained so far gives the team confidence. “As a prototype, LIPAc is already providing great value, even at this stage when it’s not yet completed. The vast amount of data obtained is helping us characterise the beam and identify improvements in the design of many sub-systems, paving the way for the final phases with continuous wave beam operations,” he explains.

The progresses in LIPAc are testimony of the complementary efforts by the European and Japanese teams. On one side, F4E provided most of the prototype’s sub-systems, in collaboration with research institutes like CEA (France), INFN (Italy), CIEMAT (Spain) and SCK CEN (Belgium), together with EUROfusion. On the other side, QST have been in charge of the facility, providing the buildings that host the accelerator in Rokkasho (Japan), as well as some sub-components. Engineers and scientists from both parties have worked hand in hand in the commissioning and operation of the machine onsite, with some supporting remotely from halfway across the world.  “The integrated project team has proved resourceful and cooperative. This spirit is essential to steer the IFMIF/EVEDA project through unprecedented conditions in accelerator technologies”, celebrates Hervé Dzitko, Programme Manager of the EU Home Team and head of the IFMIF group at F4E.

As a demonstrator for future fusion neutron sources, the plans for LIPAc go beyond the upcoming phases of operations. In fact, F4E has recently launched a call to supply an upgraded injector, the initial stage of the accelerator, with a view to improving the reliability and availability of LIPAc technologies. All-in-all, the joint efforts are proving to be solid groundwork for the facilities where Europe and Japan will study materials for fusion reactors.

For further context, watch the technical tour of the IFMIF/EVEDA project