EFFECT OF MAGNETIC TURBULENCE ON THE ION DYNAMICS IN THE DISTANT MAGNETOTAIL

The ion dynamics in the distant Earth's magnetotail is studied in the case that a cross tail, electric field Eo and reconnection-driven magn etic turbulence are present in the neutral sheet. The magnetic turbule nce observed by the Geotail spacecraft is modeled numerically by a pow er law magnetic fluctuation spectrum. The magnetic fluctuations have t he tearing mode parity with respect to the neutral sheet and are super imposed on a modified Harris sheet. A test particle simulation is perf ormed for the ions, and the particle-density, current density, bulk ve locity, temperature, pressure, and heat flux are obtained for every po int in the distant tail and as a function of the magnetic fluctuation level, delta B/B-0. It appears that the magnetic. turbulence is very e ffective in maintaining the stationary structure of the current sheet and in changing the ion acceleration due to the electric field to ther mal motion. Also, magnetic turbulence can inflate the current carrying region up to a thick current sheet, in contrast with the often assume d thin current sheet. The values obtained for the ion temperature are consistent with those observed in the distant tail by the Geotail spac ecraft. The main results are the following: (1) the thickness of the c urrent sheet increases with the level of fluctuations. The thickness l ambda corresponding to the average magnetic field current profile is o btained for delta B/B-0 similar or equal to 0.3. (2) The magnetic pres sure outside the current sheet is balanced by particle pressure for de lta B/B-0 similar or equal to 0.3. This is obtained mostly by an incre ase in the temperature, while the density profile is not much peaked i n the neutral sheet. (3) For low fluctuation levels, heating is anisot ropic, most heating going into the y direction; increasing delta B/B-0 and making reference to the local magnetic held, more heating goes in the parallel rather than in the perpendicular direction, in agreement with part of the observations. (4) A possible splitting of the bulk v elocity and of the current density in two sheets is obtained for delta B/B-0, 0.2. In general, a relevant level of magnetic turbulence, like delta B/B-0 similar or equal to 0.3, appears to be a basic ingredient of the distant magnetotail equilibrium structure.