Energization of charged particles to high energies by an induced substorm electric field within the magnetotail
Observations have shown that electrons and protons are energized up to at least 1 MeV in the magnetotail during substorms. This magnitude cannot be explained by the cross-tail electrostatic field, which typically has a modest potential difference of only 50 kV. A rotational electric field induced by a time-dependent magnetic field does not have such a limitation. In order to evaluate its capabilities a simple model of a localized, growing disturbance in the neutral sheet current was used to calculate perturbation magnetic and electric fields; the model includes the formation of X and O type neutral lines. Plasma sheet test particles were followed in these time-dependent fields by using the full relativistic equation of motion. The most efficient energizing mechanism is a two-step process, with an initial linear acceleration along a neutral line up to moderate energies, followed by betatron acceleration. The former imparts a large magnetic moment ..mu..=W/sub perpendicular//B to the particle as it begins to gyrate and drift in the magnetic field, W/sub perpendicular/ being the transverse kinetic energy. During this drift into regions of stronger magnetic field there is a large increase in W/sub perpendicular/, the relativistic invariant ..gamma mu.. remaining constant. Because of the rotational property of the induced electric field it is possible for a particle to gain energy even when the drift motion by itself would cause a loss. The model also includes acceleration along magnetic field lines in the plasma sheet, with moderate energy gain. A cyclic pattern of electron and proton precipitation is predicted, such as is observed during auroral breakup.
- Research Organization:
- Division of Geomagnetism, Finnish Meteorological Institute, SF-00101 Helsinki 10, Finland
- OSTI ID:
- 6779511
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 83:A4
- Country of Publication:
- United States
- Language:
- English
Similar Records
Numerical modeling of proton and electron bursts in a realistic magnetotail
Multiple crossings of a very thin plasma sheet in the earth's magnetotail
Related Subjects
GENERAL PHYSICS
MAGNETOTAIL
PLASMA ACCELERATION
ELECTRIC FIELDS
ELECTRON PRECIPITATION
KINETIC ENERGY
MAGNETIC BAYS
MAGNETIC MOMENTS
PLASMA SHEET
PROTON PRECIPITATION
ACCELERATION
CHARGED-PARTICLE PRECIPITATION
ENERGY
640203* - Atmospheric Physics- Magnetospheric Phenomena- (-1987)