Confinement of intense proton beams by an applied axial magnetic field in large-scale plasma

Stable and efficient transport of particle beams through plasma is a frequent topic in particle-matter interactions. In plasma, intense ion beams can focus and flap because of the self-generated electromagnetic fields and soon diverge if no restrictions are imposed. In this study, the transport of a slab beam in large-scale plasma with a uniform applied axial magnetic field is simulated and analyzed using a newly developed kinetic particle-in-cell code. The simulation results show that the applied axial magnetic field intensifies the Lorentz force acting on the beams and is effective at preventing ion-beam divergence. This confinement effect from the external magnetic field influences the beam flapping more than it does the focusing, and with increasing applied magnetic field, more beam particles converge and more energy is transferred into the transverse direction in the flapping region. In the present scenario, the beam behavior is affected synthetically by both the self-generated electromagnetic field and the external axial magnetic field. Also shown is that the applied field exerts little control over the total beam energy, which the present theoretical analysis explains well. Beam confinement by an external magnetic field is likely to have a major impact on nuclear fusion, astrophysics, and beam control.