Exploring the Focusing Mechanism of the NuMI Horn Magnets

TL;DR

This paper investigates the focusing mechanism of NuMI horn magnets at Fermilab, revealing that they generate primarily linear dipole and quadrupole fields, with muon beam profiles accurately reflecting horn current variations.

Contribution

It provides a detailed analysis of the NuMI horn focusing mechanism using muon beam profiles, highlighting the linear optics nature of the horn magnet fields.

Findings

Horn magnets produce dipole and quadrupole fields for pion focusing.

Muon beam profile detects horn current with 0.05% accuracy.

Optics of horn magnets are predominantly linear.

Abstract

Neutrinos at the Main Injector (NuMI) is a project at Fermilab that provides an intense beam of neutrinos used by a number of experiments. NuMI creates a beam of pions that decay into neutrinos, muons, and other particles. Muons are registered by the muon monitors. Magnetic horns are the key elements of the NuMI beam line. This paper uses the muon beam profile observed at the muon monitors to study the NuMI horn focusing mechanism. It is found that the horn magnet generates dipole and quadrupole fields to focus pions. This suggests that the optics of the horn magnet are predominantly linear. Our study shows that the muon beam profile accurately detects the horn current within 0.05%.