Abstract
The direct measurement of the velocity space transport of ions in a plasma is reported. Measured diffusion and convection coefficients are compared to the calculated Fokker–Planck coefficients for a fully ionized plasma. The measurements were made in a Q-machine barium plasma (Ti=Te= 0.17 eV, 5×108≤n≤8×109 cm−3) with both high and low fluctuation levels. At low fluctuation levels the measured coefficients agree with classical collision theory. Coefficients measured in the presence of large amplitude fluctuations generally are larger and have different velocity dependences. Test particle distributions are created and interrogated using the technique of optical tagging. The short-time (≪90° collision time) relaxation of the test particle distribution function was measured as a function of density and temperature of the background plasma and as a function of the velocity of the test particle distribution. The values of the convection and diffusion coefficients were extracted from these measurements. Longer time relaxations (∼90° time) also were measured.
Highlights
This paper develops the previously reported results I of the direct measurement of the velocity space transport coefficients made in a fully ionized barium plasma, under conditions close to equilibrium, in a Q-machine.2 Measurements were made by documenting the evolution of the velocity distribution of a group of test particles along the static confining magnetic field
One way to reference the relevant time scales is to use Eqs. (13) and (14) to calculate times for the tagged particle distributions to reach halfway to equilibrium. These equations were calculated for the short-time scale regime they will give an initial rate at which the test particle distribution approaches equilibrium
This work has described the direct measurement of the velocity space transport coefficients for a fully ionized ionelectron plasma
Summary
This paper develops the previously reported results I of the direct measurement of the velocity space transport coefficients made in a fully ionized barium plasma, under conditions close to equilibrium, in a Q-machine. Measurements were made by documenting the evolution of the velocity distribution of a group of test particles along the static confining magnetic field. This paper develops the previously reported results I of the direct measurement of the velocity space transport coefficients made in a fully ionized barium plasma, under conditions close to equilibrium, in a Q-machine.. Optical tagging has been used to make several transport measurements Among these are: spatial cross field ion transport in both and quiet turbulent plasmas, spatial ion transport resulting from stochastic wave-particle interaction,IO ion phase space orbits in the presence of ion-acoustic waves, II and the effects of neutral 'lpresent address: Naval Research Laboratory, Plasma Physics Division, Code 6756, Washington, D.C., 20375. The result is a low temperature, fully ionized (very few barium neutrals remain in the plasma in the area of the measurements) plasma column with equal ion and electron temperatures of the order of 0.2 eV, with minimum inherent fluctuations.
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