STRUCTURE OF THE MAGNETOTAIL CURRENT SHEET

An orbit tracing technique was used to generate current sheets for thr ee magnetotail models, Groups of ions were followed to calculate the r esulting cross-tail current. Several groups then were combined to prod uce a current sheet. The goal is a model in which the ions and associa ted electrons carry the electric current distribution needed to genera te the magnetic field B in which ion orbits were traced. The region -2 0 R(E) < x < -14 R(E) in geocentric solar magnetospheric coordinates w as studied, Emphasis was placed on identifying the categories of ion o rbits which contribute most to the cross-tail current and on gaining p hysical insight into the manner by which the ions carry the observed c urrent distribution, Ions that were trapped near z = 0, ions that magn etically mirrored throughout the current sheet, and ions that mirrored near the Earth all were needed. The current sheet structure was deter mined primarily by ion magnetization currents, Electrons of the observ ed energies carried relatively little cross-tail current in these quie t time current sheets, Distribution functions were generated and integ rated to evaluate fluid parameters. An earlier model in which B depend ed only on z produced a consistent current sheet, but it did not provi de a realistic representation of the Earth's middle magnetotail, In th e present study, B changed substantially in the x and z directions but only weakly in the y direction within our region of interest. Plasmas with three characteristic particle energies were used with each of th e magnetic field models. A plasma was found for each model in which th e density, average energy, cross-tail current, and bulk Bow velocity a greed well with satellite observations.