[Paper Review] The SPL-based Neutrino Super Beam

E. Baussan, J Bielski+26 more|arXiv (Cornell University)|Dec 4, 2012

Neutrino Physics Research17 citations

TL;DR

This paper presents a conceptual design for a high-intensity neutrino super beam at CERN using the SPL accelerator, delivering a 4 MW, 4.5 GeV proton beam to a solid titanium pebble bed target and a single magnetic horn for focusing pions. The optimized design achieves enhanced neutrino fluxes—particularly at 500 MeV and near the oscillation maximum at 260 MeV—improving CP violation discovery potential by over 30% compared to previous mercury-jet-based designs, with no show-stoppers identified in shielding or component lifetime.

ABSTRACT

The EUROnu Super Beam work package has studied a neutrino beam based on SPL at CERN and aimed at MEMPHYS, a large water Cherenkov detector, proposed for the Laboratoire Souterrain de Modane (Fréjus tunnel, France), with a baseline of 130 km. The aim of this proposed experiment is to study the CP violation in the neutrino sector. In the study reported here, we have developed the conceptual design of the neutrino beam, especially the target and the magnetic focusing device. Indeed, this beam present several unprecedented challenges, like the high primary proton beam power (4 MW), the high repetition rate (50 Hz) and the low energy of the protons (4.5 GeV). The design is completed by a study of all the main component of the system, starting from the transport system to guide the beam to the target up to the beam dump.

Motivation & Objective

• To develop a feasible, high-intensity neutrino super beam facility based on the SPL accelerator at CERN for CP violation studies.
• To address the challenges of high proton beam power (4 MW), high repetition rate (50 Hz), and low proton energy (4.5 GeV) in a novel target and horn system.
• To replace the complex mercury jet target and dual-horn system with a simpler, more robust solid titanium pebble bed target and single horn design.
• To optimize neutrino fluxes and physics performance for the MEMPHYS detector at 130 km baseline, focusing on CP violation discovery potential.
• To ensure radiological safety by thoroughly analyzing activation, shielding, and component lifetime under extreme conditions.

Proposed method

• Utilizes the SPL superconducting linac and accumulator ring to deliver 4 MW of 4.5 GeV protons at 50 Hz to the target station.
• Employs a split proton beam configuration to distribute 1 MW per beamline, reducing thermal load per device.
• Designs a packed-bed target of titanium spheres with helium coolant to efficiently remove up to 1 MW of thermal power per unit.
• Optimizes a single electromagnetic horn with pulsed current (300–350 kA) for focusing pions, using finite element modeling and transient stress analysis.
• Applies Monte Carlo simulations (FLUKA and GEANT4) to model hadronic interactions, activation, and dose rates in shielding components.
• Uses reweighting of FLUKA simulations with HARP data to improve hadro-production cross-section accuracy for flux prediction.

Experimental results

Research questions

• RQ1 Can a solid titanium pebble bed target efficiently handle 1 MW of thermal power per beamline while maintaining mechanical integrity under thermal and dynamic loads?
• RQ2 How does the performance of a single optimized magnetic horn compare to the previous dual-horn mercury-jet system in terms of neutrino flux and CP violation sensitivity?
• RQ3 What shielding thickness and configuration are required to meet radiological safety regulations for a 4 MW proton beam facility?
• RQ4 What is the predicted lifetime of the horn and target components under 50 Hz operation and high neutron fluence?
• RQ5 To what extent does the new design improve the discovery potential for CP violation in the neutrino sector compared to previous designs?

Key findings

• The titanium pebble bed target design demonstrates sufficient thermal and mechanical robustness to handle 1 MW per beamline, with preliminary analysis indicating potential for higher power operation.
• The optimized single horn design increases the νμ flux by up to 30% around 500 MeV and enhances the flux near the oscillation maximum at 260 MeV, while reducing the wrong-CP component (ν̄e, ν̄μ) by over a factor of two.
• The CP violation discovery potential at 3σ exceeds previous mercury-based designs, with the new limits (using FLUKA and HARP-reweighted models) showing improved sensitivity across the (sin²2θ₁₃, δCP) parameter space.
• Shielding requirements are substantial but feasible, with iron-lined tunnels and beam dump shielding designed to meet radiological safety standards without excessive cost or engineering complexity.
• Preliminary fatigue and neutron irradiation analysis indicate that the horn and target components are expected to survive routine 50 Hz operation for the required duration.
• The new design eliminates the need for complex mercury jet containment and dual-horn power supplies, significantly reducing technical risk and engineering complexity.