Target, magnetic horn and safety studies for the CERN to Fréjus Super Beam

The summary of the recent target and horn studies for the CERN to Fréjus neutrino beam is presented in this paper. The main design and the physics reach of the Super Beam project are described in [physicsopt]. The optimization procedure for the horn shape and layout-geometry to achieve optimum physics, the study of a target able to withstand a multi-MW proton-beam power, multi-physics simulation to investigate heat transfer, cooling and mechanical stress for the horn and safety aspects are discussed here.

A 4-MW proton-beam from CERN’s SPL is foreseen to be separated by a series of kicker magnets into four beam lines. Then each beam will be focused by a series of quadruples and correctors to a four horn/target assembly (figure LABEL:fig:_4horn). In this way, each horn/target assembly is able to accommodate better the multi-MW power and thus increasing its lifetime [protondriver].

A 0.25 mm thick beryllium beam window has been studied as the interface between each 1 MW proton-beam line and each horn/target assembly. Maximum temperatures as high as 180 ${}^{\circ }$C and (109 ${}^{\circ }$C) and Von Mises stresses as high as 50 MPa and (39 MPa) are developed respectively for water and helium cooling: these are well below the beryllium strength limit.

A packed-bed target with Ti6Al4V-spheres and helium transverse cooling has been chosen as the baseline target option [designreport, densham]. It is placed inside the upstream part of horn’s inner conductor. The advantages of the packed-bed target are among others a$)$ large surface area for heat transfer with coolant able to access areas with highest energy deposition b$)$ minimal thermo-mechanical and inertial stresses and c$)$ potential heat removal rates at the hundreds kilowatt level with high helium flow rate. Advantages of the helium transverse cooling are a$)$ almost beam neutral b$)$ no generation of stress wave in coolant and c$)$ low activation of coolant with no corrosion problems.

Alternatively, a pencil-like geometry of solid beryllium has been studied [designreport]. This pencil-like geometry gives steady-state thermal stress within acceptable range for Beryllium. Pressurized helium cooling appears feasible but center proton-beam effects could be problematic because of the stress induced: this point needs further thermo-mechanical studies.