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One of the future options to produce high intensity neutrino beams has been investigated in the framework of the EUROnu Collaboration[1]. These facility considers a 130 km baseline between the neutrino source located at CERN and the LSM (Laboratoire Souterrain de Modane) where the MEMPHYS Cherenkov detector will be installed with a fiducial mass of 0.5 MegaTons. The source will use a primary proton beam with 4-5 GeV and a power of several MegaWatts. The technological challenge will be to build a target station able to work under theses extreme conditions.
Neutrino beam production
This superbeam will benefit for the CERN developments made for the SPL (Superconducting Proton Linac)[2]. The proton beam at the end of the accumulator will have an energy range between 4-5 GeV with 4MW beam power running at 50 Hz frequency.
In order to minimise the power dissipation and limiting the radiation damages, the proton beam will be shared over four independent targets with 1MW for each target running at 12.5 Hz frequency. The secondary particle due the interaction inside the target will be focused by four magnetic horns in the tunnel producing the neutrino by decay in flight.
Beam Switchyard
A beam switchyard will distribute the protons onto the 4-targets horn system. It consists of a pair of dipoles, 4 compensating dipoles and 12 quadrupoles to route and focus the beam onto the targets at a repetition rate of 50 Hz (12.5 Hz per beam line). The length of this switchyard system is estimated to be 29.9 m [4].
Target Station
The four horn system is foreseen to work with a high intensity (350 kA) pulsed current at 12.5 Hz frequency. A 20 kW power will be dissipated by the structure. In case of one horn is damage, the beam will be shared over the others. Hence, each horn has to work under a 1.3 MW beam power.
Target
The target contains titanium spheres in a cylinder with holes. A jet of Helium at a 10 bar pressure will circulate permanently inside allowing to cool the target. This geometry allows to increase the surface with the gas and minimize the mechanical constraints due to the impact of the protons inside the target.
Magnetic horn
The body of the horn is made of aluminium alloy Al 6061 T6 which offers a good compromise between mechanical stress, good resistance to corrosion and good electrical conductivity. The wall thickness has to be as thin as possible to ensure optimal physics performances and to limit the energy deposition inside from the secondary particles escaping the target. The mechanical constraints, due to magnetic pressure has been calculated with a finite element based model. The lifetime of the horn reaches a maximum for a stress less than 30 MPa and an uniform temperature of 60°C. In order to maintain a constant temperature of the horns, water jets around their body are foreseen. The water flow inside each horn will be 60 to 120 l/min.
Power Station
The current is supplied to the horn thanks to an electrical transmission lines 33 m long and eight aluminium conductors with a rectangular section 60 cm x 2 cm. These geometrical dimensions have been calculated in order to reduce the resistivity and the inductance. The power station will be located in a special room 180m2 which will be able to support a specific weight of 1 ton/m2. The electrical consumption of 1.3 MW with a total dissipated power of 243 kW by water cooling and 280 kW by air.
Building
The building concept will include the target station consisting of the four magnetic horns equipped with their target. The decay tunnel length reach 25 m. A special hot cell able to manipulate highly radioactive material is foreseen for repairing or replacement of horn with a specific equipment.
References:
[1] EUROnu WP2 Website
[2] Conceptual design of the SPL II : A high-power superconducting H− linac at CERN : CERN-2006-006
[3] The SPL Neutrino Super Beam arXiv:1212.0732
[4] Preliminary Design of a 4 MW Proton Beam Switchyard for a Neutrino Super Beam Production Facility, E. Bouquerel et al., Conference: C13-05-12, TUPWO004, IPAC2013 Proceedings, 2013.