Chaotic Scattering of Pitch Angles in the Current Sheet of the Magnetotail
Abstract
The process of pitch angle scattering by a current sheet is studied using the modified Harris field model. The relationship between the incoming asymptotic pitch angle α_{in} and the outgoing asymptotic pitch angle α_{out} is studied from first principles by numerically integrating the equation of motion. We give evidence that charged particles undergo chaotic scattering by the current sheet. For fixed α_{in}, it is shown that α_{out} exhibits sensitive dependence on the energy parameter Ĥ in certain energy ranges. For fixed Ĥ in the same energy ranges, α_{out} sensitively depends on α_{in}. For other energy values, α_{out} does not show sensitive dependence on α_{in} for most phase angles. The latter energy values occur at the resonance values given by the previously identified relationship Ĥ^{1/4}~N+0.6. Thus α_{out} exhibits no significant sensitivity near these resonance energies. This conclusion applies to a range of α_{in} centered at α_{in}=0 (i.e., field aligned in the asymptotic region). A distribution of α_{in} is mapped from the asymptotic region to the midplane, and it is found that the resulting particle distribution should have beam structures with wellcollimated pitch angles near each resonance energy value. Implications for the particle distribution functions in the Earth's magnetotail are discussed.
 Publication:

Journal of Geophysical Research
 Pub Date:
 May 1992
 DOI:
 10.1029/91JA03020
 Bibcode:
 1992JGR....97.6479B
 Keywords:

 Chaos;
 Charged Particles;
 Current Sheets;
 Geomagnetic Tail;
 Pitch (Inclination);
 Scattering;
 Distribution Functions;
 Equations Of Motion;
 Mathematical Models;
 Numerical Integration;
 Particle Beams;
 Geophysics;
 Magnetospheric Physics: Magnetotail;
 Space Plasma Physics: Charged particle motion and acceleration;
 Space Plasma Physics: Nonlinear phenomena