DTIC ADP012537: Shear Limited Test Particle Diffusion pdf

DTIC ADP012537: Shear Limited Test Particle Diffusion

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Measurements of test-particle diffusion in pure ion plasmas show 2D enhancements over the 3D rates, limited by shear in the plasma rotation omega epsilon (r). The diffusion is due to “long-range” ion-ion collisions in the quiescent, steady-state Mg+ plasma. For short plasma length Lp and low shear S (equivalent to) r partial derivative omega epsilon/partial derivative r, thermal ions bounce axially many times before shear separates them in theta, so the ions move in (r, theta) as bounce averaged “rods” of charge (i.e. 2D point vortices). Experimentally, we vary the number of bounces over the range 0.2 </= N(sub b) </= 10,000. For long plasmas with N (sub b) </= 1, we observe diffusion in quantitative agreement with the 3D theory of long-range E x B drift collisions. For shorter plasmas or lower shear, with N(sub b) > 1, we measure diffusion rates enhanced by up to 100X.

For exceedingly small shear, i.e. N(sub b) >/= 1000, we observe diffusion rates consistent with the Taylor-McNamara estimates for a shear-free thermal plasma. Overall, the data shows fair agreement with Dubin’s new theory of 2D diffusion in shear, which predicts an enhancement of D(sup 2D)/D( sup 3D) N(sub b) ^ N(sub b) up to the Taylor-McNamara limit

• Creator/s: Defense Technical Information Center
• Date: 6/24/2002
• Year: 2002
• Book Topics/Themes: DTIC Archive, Anderegg, Francois, Driscoll, C.. F., Dubin, Daniel H., CALIFORNIA UNIV SAN DIEGO LA JOLLA, *SHEAR PROPERTIES, *TWO DIMENSIONAL, *PLASMAS(PHYSICS), THERMAL PROPERTIES, MAGNESIUM, SYMPOSIA, PURITY, DIFFUSION, RODS, PARTICLE COLLISIONS, ION ION INTERACTIONS

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