ARE PARTICLES DETRAPPED BY CONSTANT B-Y IN STATIC MAGNETIC REVERSALS

Single-particle dynamics in simple models for the static reversing mag netic field of the geotail current sheet have been extensively studied in the case where the reversing field B-x(z) varies, the linking fiel d B-z is constant, and the crosstail field B-y is zero (and some gener alization to include time dependence has been achieved). More recently , numerically integrated trajectories in static reversals which includ e a constant shear B-y component have suggested some differences in th e nature of the dynamics in this and the B-y = 0 case. The invariant o f the z cross-sheet motion for the B-y = 0 case is well known, here we find its equivalent for systems with constant B-y. Our results hold f or reversals with general z dependence and arbitrary constant B-y. The form of this invariant suggests that it is still conserved for trappe d particles, but for certain values of energy, B-y and B-z, the invari ant is destroyed and particles are detrapped. This corresponds to an i ncrease in the volume in phase space available to current carrying par ticles that transit the sheet. For typical magnetotail parameters, bot h protons and electrons in an average 1 R-E thick sheet will be detrap ped, but in a thin similar to 100 km sheet protons will not.