Optimising the Target and Capture Sections of the Neutrino Factory

Abstract

The Neutrino Factory is designed to produce an intense high energy neutrino beam from stored muons. The majority of the muons are obtained from the decay of pions, produced by a proton beam impinging on a free-flowing mercury-jet target and captured by a high magnetic field. It is important to capture a large fraction of the produced pions to maximize the intensity of the neutrino beam. Various optimisation studies have been performed with the aim of maximising the muon influx to the accelerator and thus the neutrino beam intensity. The optimisation studies were performed with the use of Monte Carlo simulation tools. The production of secondary particles, by interactions between the incoming proton beam and the mercury target, was optimised by varying the proton beam impact position and impact angles on the target. The proton beam and target interaction region was studied and showed to be off the central axis of the capture section in the baseline configuration. The off-centred interaction region resulted in off-centred secondary particles. A new proton beam definition was introduced to bring the secondary particle back on the central axis. The path length was increased by varying the proton beam impact position and impact angles on the target while keeping the production of secondary particles centred. The optimisations increased the muon influx to the accelerator. In addition shape fluctuations of the free-flowing mercury jet target was introduced and studied. The study showed only a small performance decrease. The capture efficiency of the capture and tapering sections was studied by using alternative solenoid magnet geometries, alternative solenoid magnet configurations and therefore alternative magnetic field tapering variants to the baseline configuration. In addition an alternative shielding layout was proposed. The optimised capture and tapering sections increases the capture efficiency by using a simple three solenoid magnet configuration and a rapidly tapered magnetic field. The Muon Ionisation Cooling Experiment (MICE) is an on-going proof of principle experiment. The MICE cooling channel is designed according to a feasibility study which assumes an incoming muon beam with symmetric momentum distribution. The MICE beam line delivers a muon beam with a skewed momentum distribution to the experiment. Therefore the MICE beam line was tuned by varying the magnetic field strength in the first dipole to provide a symmetrical momentum distribution to MICE. Both Monte Carlo simulations and data from MICE were used in the study. In addition the pion contamination levels of the MICE muon beams were studied by using results from Monte Carlo simulations.