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A magnetized plasma is one in which the ambient magnetic field
is strong enough to significantly alter particle
trajectories. In particular,
magnetized plasmas are anisotropic, responding differently to
forces which are parallel and perpendicular to the direction
of . Note that a magnetized plasma moving with
mean velocity contains an electric field
which is not affected
by Debye shielding. Of course, in the rest frame of the plasma the electric
field is essentially zero.
As is well-known, charged particles respond to the Lorentz force,
by freely streaming in the direction of , whilst executing
circular Larmor orbits, or gyro-orbits, in the plane perpendicular to .
As the field-strength increases, the resulting helical orbits become more
tightly wound, effectively tying particles to magnetic field-lines.
The typical Larmor radius, or gyroradius, of a charged particle
gyrating in a
magnetic field is given by
is the cyclotron frequency, or gyrofrequency, associated with the
gyration. As usual, there is a distinct gyroradius for each species.
When species temperatures are comparable, the electron gyroradius is
distinctly smaller than the ion gyroradius:
A plasma system, or process, is said to be magnetized if its
characteristic length-scale is large compared to the gyroradius.
In the opposite limit, , charged particles have essentially
straight-line trajectories. Thus, the ability of the magnetic field to
significantly affect particle trajectories is measured by the
There are some cases of interest in which the electrons are magnetized, but the
ions are not. However, a ``magnetized'' plasma conventionally refers to
one in which both species are magnetized. This state is generally achieved
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