PARTICLE ORBITS IN MODEL CURRENT SHEETS WITH A NONZERO BY-COMPONENT

The problem of charged particle motions in magnetotaillike model current sheets (Speiser, 1965) is revisited with the inclusion of a nonzero dawn-dusk magnetic field component B(y). In a zero B(y) current sheet, particle orbits in the phase space (z', z) are symmetric about the z = 0 plane for most models as long as B(z) is z-independent and antisymmetry of B(x) about z = 0 is assumed, i.e., B(x)(z) = -B(x)(-z). This can be clearly seen from the fact that the equations of motion for charged particles are unchanged when z is changed to -z. In a nonzero B(z) current sheet, this symmetric character in the phase space does not exist. Assuming a small B(y) (same order as B(z)), three cases are examined in this paper: case 1: B(x) not-equal 0, B(y) not-equal 0, B(z) = 0, and E(y) = 0; case 2: B(x) not-equal 0, B(y) not-equal 0, B(z) = 0, and E(y) not-equal 0 for ''trapped'' particles; and case 3: B(x) not-equal 0, B(y) not-equal 0, B(z) not-equal 0, and E(y) not-equal 0 for ''escaped'' particles. Our study shows that a nonzero B(y) component can disturb particle orbits, change their bounce frequency, and destroy the symmetry of the orbits about the z = 0 plane. For the escaped particles, acceleration and ejection of particles from the current sheet are mainly controlled by the zero B(y) current sheet system. However, with the injection of low energy particles, positively (negatively) charged particles, after acceleration by the current sheet, tend to be ejected toward the northern (southern) boundary of the current sheet for a positive B(y) component (i.e., dawn to dusk), and toward the opposite direction for a negative B(y) component. We present several examples of test particle computations for a parabolic model.