Spatial Ion Transport
(Quiet, Turbulent, Magnetized, Unmagnetized Plasmas)

Experiments at Irvine study the diffusion and convection of plasma ions across space. We have done experiments where the classical, Coulomb collisions are dominant ("Quiet Plasmas" discussed below). Other experiments have studied plasmas with sufficient electrostatic turbulence that the diffusion is no longer classical ("Turbulent Plasmas" below). These experiments have been done and are being performed in plasmas which are magnetized or unmagnetized. The issue of ion magnetization is simple: are ion motions essentially Larmor orbits with occasional collisions or is the ion collision frequency high enough so ion motion between collisions is best described by rectilinear motion? Is the effective diffusive collision frequency greater or less than the ion gyro frequency? Archived journal references on the experiments described below are at Lab Publications.

Quiet Plasmas:

Our magnetized quiet plasma ion diffusion results are summarized in the figures below. The experiments showed agreement of observed ion diffusion with the classical test particle predictions without any normalization.

Test ion diffusion versus plasma density; classical prediction is linear dependence shown by Dii. Bohm and turbulent predictions shown also.	Ion diffusion versus confining magnetic field. Again, the classical prediction is Dii.

Turbulent Plasmas:

Turbulent diffusion in a magnetized plasma has been studied by varying the background electrostatic fluctuation level. Via parametric decay of lower hybrid waves into electrostatic ion cyclotron waves, the ion-perturbing fluctuation level could be controlled by the experimenter. The resulting dependence of ion diffusion on fluctuation level is shown at right. A clearly linear dependence of D on fluctuations was observed over the range of fluctuations studied. The lower left point on the graph is the classical diffusion level observed with a small amount of incipient fluctuations. Figure shows: Cross-Field ion diffusion versus low-frequency ion density fluctuation level. Dashed line, theory; solid line, linear least-squares fit to data.

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