Three-dimensional particle-in-cell simulations of the spoke-like activity in a Penning discharge

Hall plasmas, confined by crossed fields (E×B) with magnetized electrons and unmagnetized ions, exhibit high plasma density at low pressures and have been employed in advanced plasma sources for industry, such as for Hall thrusters, magnetrons and Penning discharges. In certain applications, such as Penning discharges of particular interest in this study, the spoke-like activity refers to the widely reported azimuthally rotating structure with increased plasma density. However, the underlying mechanism responsible for the formation of this structure has not been studied numerically in a 3D kinetic sense. Therefore, in this study, we aim to investigate the spoke-like activity within a Penning discharge by employing the LTP-PIC (Low Temperature Plasma Particle-In-Cell) code. Our simulations reveal that, at steady state, the plasmas behave as a rigid body experiencing low-frequency precession with a tilt angle along the axis, resembling the structure of a spoke. Analysis indicates that the initial displacements of electron and ion centroids are caused by the electron-hose instability. A centroid theory that incorporates both electron and ion motions is proposed to predict the rotation frequency.