HYBRID SIMULATIONS OF THIN CURRENT SHEETS

A one-dimensional, hybrid simulation code is used to study current sheets with a nonzero normal magnetic field B(z) and a dawn-to-dusk electric field E(y). Such configurations are dependent upon only two parameters: we use the normalized normal magnetic field B(z) = B(z)/(4pin(b)v(T)2)1/2 and normalized electric field v(D) = (1/v(T)) (cE(y)/B(z)), where v(T) is the thermal velocity of ions prior to their interaction with the current sheet and nb is the number density outside the current sheet (at the simulation boundary). A third parameter that is relevant to the motion of particles in current sheets is kappa(A), the value of kappa = (R(min)/rho(max))1/2 for particles of average energy. We find that if either B(z) is close to or greater than 1, or if kappa(A) is close to 1, a rotational mode develops in which the z = 0 current rotates with the ion sense about the normal magnetic field, while for small values of both B(z) or kappa(A), the configuration is quasi-steady. To achieve values of kappa(A) of the order of or larger than 1, we decrease the value of v(D) uniformly. We find that the magnetic field fluctuations and particle distribution functions are similar in many respects to what was observed in the day 240, 1986, AMPTE/CCE current disruption event (Takahashi et al., 1987), an event that appears to be located at the site of initiation of current disruption and related particle energization (Lui et al., 1992).