Dual-Species Plasmas Illustrate MHD Flows

Plasma loops created in the laboratory strongly resemble structures observed in the solar corona. For example, both solar coronal loops and experimental loops exhibit remarkably uniform axial cross sections. A magnetohydrodynamic theory that was proposed to explain this phenomenon predicts that a plasma loop whose axial magnetic field is constricted at both footpoints will experience bulk flows into the loop from both ends. To test this theory, dual-species plasma loops were formed by supplying a different neutral gas to each of the two footpoints. Optical filters were then used to separately image the motion of different sections of the plasma. Bulk flows were, in fact, observed.