Simulation of Alpha Particles in Rotating Plasma Interacting With a Stationary Ripple

Abstract—Superthermal E ×B rotation can provide magne-tohydrodynamic stability and enhanced confinement to axisym-metric mirrors. However, the rotation speed has been limited by phenomena at end electrodes. A new prediction is that rotation might instead be produced using a magnetic ripple and alpha particle kinetic energy, in an extension of the alpha channeling concept. The interaction of alpha particles with the ripple results in visually interesting and practically useful orbits. Index Terms—Magnetic confinement, plasma devices, plasma simulation, plasma waves. AXISYMMETRIC mirrors have many potential advantagesas fusion reactors including high beta, steady-state op-eration, and a simple coil configuration [1]. The major issues that must be overcome by axisymmetric mirrors are magneto-hydrodynamic (MHD) stability and excessive parallel energy loss. Both of these may be addressed by inducing superthermal E ×B rotation, which provides MHD stability through veloc-ity shear and increases axial confinement by the centrifugal force [2]–[4]. In past experiments, the rotation has been pro-duced by electrodes in the mirror throat, and these electrodes limited the rotation speed to the Alfven critical ionization velocity (CIV) [2], [5], [6]. However, rotation might best be produced by waves rather than electrodes, allowing the CIV limit to be overcome [7]. The method of driving rotation with waves is an extension of the alpha channeling effect in tokamaks [8]. In alpha channel-ing, waves are injected which create a diffusion path connecting the hot core of the plasma to the cold edge. That is, there is coupled diffusion in energy and position. As alpha particles interact with the wave, they diffuse radially and may eventually exit at the outer edge. Because the radial diffusion is related to diffusion in energy by the wave properties, alpha particles can be made to exit at low energy, transferring their energy to the wave. The wave energy can then be used for heating ions or other purposes [9]