Poster Summaries Part H: The EUROnu Neutrino Oscillation Super Beam

Nikolaos Vassilopoulos on behalf of EUROnu WP2 group: The EUROnu Neutrino Oscillation Super Beam

In the framework of the EUROnu design study, a new design for the CERN to Fréjus neutrino beam based on CERN Superconducting Proton Linac has been achieved. This Super Beam is able to discover a CP violation in the leptonic sector over a significant fraction of deltaCP parameter by using a 4-MW proton beam of 4.5 GeV/c, a baseline of 130 km and the future Water Cherenkov MEMPHYS detector (0.5 Mton fiducial mass). The neutrino mass hierarchy can also be discovered by combining atmospheric neutrino data. After discovering that the last neutrino oscillation angle theta13 was large, it came out that working on the second oscillation maximum is even more promising. Thus, using the same parameters than for CERN to Fréjus, CERN to Canfranc with a baseline of 650 km has even more physics potentialities.

This study is the first that presents a clear and complete conceptual design for a very challenging facility, capable of delivering a low energy neutrino beam with a 4 MW 4.5 GeV/c proton driver. We have presented a novel design for the target, using both a split proton beam to divide the power on each device by a factor four and a pebble bed target. The latter allows the coolant to dissipate in a very efficient way the heat, flowing through the innermost part of the target. The structure of the Ti spheres is such that they will stand the static and dynamic stresses. Preliminary calculations show that this target will be able to stand not only 1 MW per device, as originally required, but probably a higher power. This feature makes it a very attractive solution also for other facilities and in particular it could serve as the target of a neutrino factory. The focusing device, a magnetic horn, based on a conventional design, has been optimized for our needs on the basis of new approach that allow to study a large parameter space, defined by its geometry, material thickness, current and the decay tunnel characteristics. This optimization has allowed to maintain the excellent physics performances while offering a realistic design. Preliminary study conclude that the lifetime of each device will be sufficient for a routine operation with high reliability. A difficult but key component is the power supply, subject to an unusual high repetition rate of 50 Hz for a peak current of 350 kA.

We have studied most of the system features, starting from the proton beam exiting from the accumulator up to the beam dump. This has required a diverse array of complementary competences and studies which are only briefly summarized here. Our main conclusion is that this project is feasible by adopting the novel approach that we have introduced and developed here. We have fully studied the shielding and activation issues, to comply with existing radiological regulations, and found that the shielding type and thicknesses, while sizeable, are not excessive neither in terms of engineering nor of cost. In general, while some of the problems that we had in front of us at the start of the project were particularly challenging, we have found no show-stopper and are confident that this project could be built. Of course, this study, developed within the context of EUROnu, was limited to the engineering and simulations levels. Some of the devices considered here are novel and would require an extensive phase of R/D to assess their performances and validate with a prototype their use in this context.

The following left figure shows the fraction of deltaCP for CERN to Fréjus (SPL1) and to Canfranc (SPL2) and other future neutrino beams. Right figure shows the mass hierarchy performance without taking into account atmospheric data for SPL.