Structure and dynamics of a magnetic neutral loop discharge plasma described using electron motion in a quadrupole magnetic field

Abstract

Electron motion in a CF4 magnetic neutral loop discharge (NLD) plasma was simulated using a Monte Carlo method. The spatial distribution of electrons illustrated the fundamental structure of the NLD plasma, and its dynamics were depicted from the distributions of the mean electron energy, the electron energy gain and the azimuthal electron flux. The peak of mean electron energy appeared at the neutral loop (NL), which confirmed that electrons gain energy near this loop. High mean electron energy was observed not only near the NL but also along the separatrices of the quadrupole magnetic field. Energetic electrons were transported along the separatrices and induced ionization at those locations. However, the electron distribution had valleys along the separatrices, because electrons accelerated near the NL were likely to leave this region where the binding of the magnetic field is weak. The azimuthal electron flux representing the loop plasma current showed that the electron conduction path around the NL, which has conventionally been modelled as a ring conductor, has a particular directionality due to the rectification effect of antiparallel magnetic fields composing the quadrupole magnetic field. The directionality in the upper and lower regions of the quadrupole magnetic field was opposite to that in the inner and outer regions.