Collisions in gaseous plasmas are fundamentally different from collisions in neutral gases because a charged particle interacts simultaneously with many others via the Coulomb potential. This difference is not as intuitive for students as the billiard ball like collisions of neutral particles. We present trajectories of electrons in a weakly coupled plasma obtained from particle simulations. The trajectories illustrate the concept of distant collisions and the variation of the free path with energy, which has major consequences in plasma physics.
REFERENCES
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Lyman
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More details of the -body techniques for plasma simulations can be found in
A.
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Particles moving faster than the thermal ions can only be shielded by electrons; particles moving faster than the thermal electrons are not shielded at all and produce Langmuir waves. In the absence of equilibrium and/or for dimensions different from three, the shielding may be very different from the conventional one. See, for example,
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For collisions between electrons the calculation must be done in the center-of-mass frame, and the mean free path for change in the velocity direction is greater by a factor of about 2.
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See
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Adapted from
N.
Meyer-Vernet
, Basics of the Solar Wind
(Cambridge U.P.
, Cambridge
, 2007
).© 2008 American Association of Physics Teachers.
2008
American Association of Physics Teachers
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