Under and over-adiabatic electrons through a perpendicular collisionless shock: theory versus simulations
Test particle simulations are performed in order to analyze in detail the dynamics of transmitted electrons through a supercritical, strictly perpendicular, collisionless shock. In addition to adiabatic particles, two distinct nonadiabatic populations are observed surprisingly: (i) first, an <...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2005-12-01
|
| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/23/3685/2005/angeo-23-3685-2005.pdf |
| Summary: | Test particle simulations are performed in order to analyze in detail the
dynamics of transmitted electrons through a supercritical, strictly
perpendicular, collisionless shock. In addition to adiabatic particles, two
distinct nonadiabatic populations are observed surprisingly: (i) first, an
<I>over-adiabatic</I> population characterized by an increase in the gyrating
velocity higher than that expected from the conservation of the magnetic
moment µ, and <I>(ii)</I> second, an <I>under-adiabatic</I> population
characterized by a decrease in this velocity. Results show that both
nonadiabatic populations have their pitch angle more aligned along the magnetic
field
than the adiabatic one at the time these hit the shock front. The formation of
"<I>under</I>" and "<I>over-adiabatic</I>" particles strongly depends on
their local injection conditions through the large amplitude cross-shock
potential present
within the shock front.
A simplified theoretical model validates these results and points out the
important role of the electric field as seen by the electrons. A classification
shows that both nonadiabatic electrons are issued from the core part of the
upstream distributionÊ function. In contrast, suprathermal and tail electrons
only contribute to the adiabatic population; nevertheless, the core part of the
upstream distribution contributes at a lower percentage to the adiabatic
electrons. <I>Under-adiabatic</I> electrons are characterized by small
injection angles θ<sub><i>inj</i></sub>≤90°, whereas
"<I>over-adiabatic</I>" particles have high injection angles
θ<sub><i>inj</i></sub>>90° (where θ<sub><i>inj</i></sub> is the angle between the local gyrating
velocity vector and the shock normal). |
|---|---|
| ISSN: | 0992-7689 1432-0576 |