The ESS installation is comprised of a linear proton accelerator, a tungsten target and instruments arranged around the target. The neutrons are produced by accelerating the protons onto the target (i.e., by spallation). The diagnostics provided by IRFU relate to the low-energy transport line where different types of ions extracted from the source still coexist. At higher energy, only the protons are accelerated.

Although these ions have identical energy, their masses, and therefore their velocities, differ. An optical diagnostic collecting the light emitted during the neutralization of ions makes it possible to measure the Doppler shifts associated with such speed variations and, therefore, to determine the purity of the ion beam. The purity expected, on the order of 80%, was measured on the source developed for ESS in Catania, Italy.

The other beam parameter to be checked is the vergence (whether convergence or divergence), which is measured using an emittance-meter. The device developed by IRFU and CEA-LITEN was also successfully tested in Catania.

The success of the acceptance tests completed in January 2017, as well as the delivery of the diagnostics in Lund, is the official completion of two contracts between CEA and ESS.