Magnetic Field Imaging by Cosmic-ray Muon (Magic-µ) – concept and overview –

Cosmic-ray muon radiography, also called muography, includes two main techniques: the absorption and scattering methods. The absorption method, first proposed by Alvarez in 1970 to search for hidden chambers in pyramids, has been applied in recent times to various large targets to inspect their density distribution or inner structure. The scattering method, invented by Borozdin in 2003, allows to also identify nuclides, especially heavy ones such as uranium or plutonium. This study proposes a new approach, which aims at measuring magnetic fields. We call the project Magic-µ, which is short for MAGnetic field Imaging by Cosmic-ray MUons. When passing through a magnetic field, charged particles are deflected and change their trajectories without losing kinetic energies. The charge of the muons, positive or negative, determines in which direction the trajectory is shifted. Given a magnetic flux density and a trajectory length in the magnetic field, by measuring the shift in trajectory we can uniquely determine the magnetic flux density along the trajectory. We propose a muography set-up with sensitivity to magnetic fields, and data analysis methods to estimate a 3-dimensional magnetic flux density. In the present paper, we outline the key points of the Magic-µ project and its prospects.