"Adlam and Allen and Davis, Lust, and Schluter have studied nonlinear plane-waves, propagating normal to the magnetic field, in a cold plasma. One solution of particular interest is a solitary wave, or single pulse. We present a method for solving the analogous problem for a plasma with finite temperature, in the limiting case where the amplitude of the wave is small and where, consequently, the width of the waver is very large."

Both in magnetohydrodynamic shocks and in accelerated partially ionized gas flow across a magnetic field, space charge separation occurs that establishes very large electric fields in the direction of motion. The width of the current layers associated with the acceleration is never less than the electron Larmor radius with no collisions and is broadened by electron collisions to a width solely determined by the effective resistivity. The electrons gain an energy regardless of collisions equal to the electric potential difference across the layer. This potential corresponds to the change in kinetic energy of mass motion per ion. For slightly ionized gases, the additional stress of neutral ion collisions within the layer can make the electric potential and hence gain in electron energy very large for only modest changes in mass velocity. Hence ionization may occur when the change in kinetic energy of the ions is small compared to the ionization potential.

In choosing a model to describe the behavior of a plasma, a balance must be maintained between the simplicity of a macroscopic description and the detail in a microscopic description. In an ordinary gas, the criterion for behavior as a continuum is that the mean-free-path be small. In a plasma there is a similar criterion; other lengths (Debye, Larmor) may complicate the macroscopic equations but will not destroy their validity. An entirely different criterion (in a collisionless plasma) is that the Larmor radius be small. A consistent treatment of just the lowest order guiding-center particle motion is sufficient to yield, with a minimum of computation, both a microscopic theory (guiding-center gas) and a macroscopic continuum theory (guiding-center fluid). A comparison shows why certain types of arguments conventionally phrased in microscopic terms are exactly equivalent to a potentially less exact macroscopic analysis. (auth)

This is the monthly report for the Hanford Laboratories Operation, February 1961. Metallurgy, reactor fuels, chemistry, dosimetry, separation processes, reactor technology, financial activities, visits, biology operation, physics and instrumentation research, and employee relations are discussed.