Magnetic field structure at the diamagnetic cavity boundary (numerical simulations)

A three-dimensional adaptive grid MHD simulation of the solar wind interact ion with comet Halley shows that the boundary of the diamagnetic cavity is a closed, well defined surface. On this surface magnetic field neutral poin ts should exist, and indeed, two O-type neutral points were found at the ca vity boundary. In addition, the transition from closed magnetic field lines around the diamagnetic cavity to open field lines in the comet tail requir es the formation of at least one X-type neutral point. Such a neutral point was also found in the simulated cometary ionosphere downstream from the ca vity. The results of numerical simulations show that the plasma density nea r the neutral points increases significantly. This increase seems to be ind icative of plasma escape from the diamagnetic cavity in the neighborhood of the neutral points, resulting in plasma jets.