Energetic Ion Beam-Plasma Interactions.
Final rept. 1 Mar 81-28 Feb 83,
PRINCETON UNIV N J PLASMA PHYSICS LAB
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The main effort was to understand the physics of a very energetic ion beam propagating through a magnetized plasma roughly perpendicular to the magnetic field. It has been appreciated for several years that the central problem is the charge neutralization of this beam. For conditions where ion beam number density is comparable or larger than plasma number density, the motion of the electrons is quite complicated being controlled by the self fields produced by their motion. Thus, to solve this problem it was necessary to construct a rather complex computer code. During the first year of work the general nature of the electron motion was elucidated and a 2-D model for the problem was constructed that was sufficiently realistic to answer the charge neutralization question in general. A rough indication of the necessary amount of charge neutralization, defined as the ratio of the difference of electron and ion number densities in the beam to the ion beam density, obtained and shown to be vc if the beam divergence is small enough. Also it was shown that the beam would move along a circular orbit with radius equal to the cyclotron radius of an individual beam ion. It was shown that the required axial variation to attain desired charge neutralization were easy to achieve in practice. Thus, it appears entirely possible to propagate an energetic ion beam a long distance through a plasma and to hold it together radially against expansional forces.
- Plasma Physics and Magnetohydrodynamics