Studies on the characteristics of dipole magnetic field-confined plasmas and their interaction with charged particle beams are critical to the near-Earth magnetospheric plasma research. In this paper, a fully relativistic electromagnetic Particle-in-Cell (PIC) method, implemented with the open-source code Smilei, is used to perform three-dimensional kinetic simulations on the evolution of electron beams injected into the dipole magnetic field confined plasmas. The simulation adopts a uniform grid with 256 cells in each spatial direction, neglects collisional effects, and considers a plasma consisting only of electrons and ions. The initial plasma is configured as a rectangular toroidal structure with a square cross-section, a number density of 1×10¹² m^-3. An externally prescribed dipole magnetic field is applied in the simulation domain, generated by an ideal current loop centered in the x-y plane of the grid (the loop radius is 1/8 of the grid length, and the current magnitude is 4000 A), with a maximum magnetic field strength of 6000 G. Under these conditions, the ratio of electron plasma frequency to gyrofrequency ranges from 5.3×10^-4 to 3.2, and the plasma beta varies from 2.24×10^-10 to 8×10^-3. The grid cell size is set to 0.05 times of the electron Debye length, and the time step is 0.95 times of the CFL time step. The simulation is run for a total of 20000 steps to ensure the achievement of a quasi-steady state. The electron beams with a temperature of 10 eV and a drift velocity of 1×10⁷ m/s are injected from the x-min boundary of the grid with different angles (0°, 30°, 60°) relative to the positive x-axis, to explore the impact of electron beams with varying injection angles on the dipole magnetic field confined plasma.
The simulation results illustrate the spatiotemporal evolution and behavior of the electron beam and plasma. Specifically, the plasma confined by a dipole magnetic field forms a crescent-shaped shell structure aligned with magnetic field lines, with toroidal currents of opposite directions generated inside and outside the shell. When the electron beam is injected at incident angles of 0° and 30°, drift effects cause most beam particles to concentrate along a specific magnetic field line on the x=y plane. Additionally, the drift current induced by electron beam injection alters the distribution of the central toroidal current in the main plasma, resulting in localized enhancement and attenuation of the toroidal current. In contrast, at an injection angle of 60°, the overwhelming majority of beam particles are scattered by the dipole magnetic field and fail to reach the central region for interaction with the main plasma. Simulation findings further indicate that when the electron beam’s injection angle relative to the magnetic field direction exceeds 20° and its drift velocity is misaligned with the dipole field center, most beam particles scatter and are ejected from the simulation domain, precluding interaction with the dipole-confined plasma. For future experimental devices investigating the interactions between electron beam and plasma in dipole magnetic field confinement systems, selecting an appropriate beam injection direction is critical to ensure the electrons can access the core region of the dipole field and interact with the confined plasma. This study yields valuable insights into the dynamic behavior of plasma in dipole magnetic fields, and is helpful for enabling China’s space plasma research facilities to achieve their designed scientific goals.