The advanced equipment used by particle physicists to search for charged particles such as neutrinos and cosmic rays picks up extremely faint light bursts that are released when incident particles interact with a medium. The most popular of these devices, known as Cherenkov detectors, use photomultiplier tubes to collect as much of this light as they can. This gives rise to a significant signal that can be used to extract details about the source particle. However, the Earth’s magnetic field causes them to lose efficiency.
Sara Rodriguez Cabo of the University of Oviedo, Spain, and her colleagues have now shown in a study published in EPJ P how particular configurations of wire coils that transport current around huge cylindrical detectors can make up for natural magnetic disturbances and shield photodetectors from them.
External magnetic fields, particularly that of the Earth, impact the paths of low-energy electrons in a photomultiplier tube. When the field direction is perpendicular to the tube axis, it creates sensitivity fluctuations in the anode that collects the electrons, lowering photon-collection efficiency. Placing current-carrying wire coils near Cherenkov-type detectors can aid by creating another field that compensates for the Earth’s.
Cabo and her colleagues investigated the impact of several characteristics on this compensation. They examined how the coil-generated magnetic field intensity and direction varied with detector size, distance between coils, and current strength in a series of simulations.
They discovered that by adding coils with highly specific geometry and position to the basic arrangement, they were able to address magnetic fields in parts of the detector that would normally be difficult to control.
According to the researchers, 99.5% of the photomultiplier tubes in their simulations have an efficiency loss of less than 1% due to magnetic fields. They believe that careful consideration of coil design and position can help to conceal sensitive parts of the detector.
Cabo, S. R., et al. (2023) Magnetic shielding simulation for particle detection. The European Physical Journal Plus. doi:10.1140/epjp/s13360-023-04520-1