We report a further advance in the bulk purification of nitric acid-treated single-walled carbon nanotubes (SWNTs) by use of high-speed centrifugation. We have already shown that low-speed centrifugation is effective in removing amorphous carbon (AC). In these earlier experiments, the AC preferentially suspends in aqueous dispersions on low-speed centrifugation (2000g), leaving the SWNTs in the sediment. In a surprising reversal, we now show that high-speed centrifugation (20000g) of well-dispersed preparations is effective in sedimenting carbon nanoparticles (CNP), while leaving the SWNTs suspended in aqueous media. Taken together, these two techniques allow the bulk scale (10 g) purification of SWNTs by efficiently separating the two main contaminants, in an industrially viable process. We show that the mechanism of these separations is based on the differential charging (zeta-potential) of the AC, CNPs, and SWNTs that comes about during the chemical processing. Due to their more robust structure, nitric acid oxidation leaves the CNPs with a surface charge density lower than that of the SWNTs, and thus the CNPs do not form stable dispersions in aqueous media during high-speed centrifugation. The efficiency of the process was confirmed by the high purification recovery factor (PRF = 90%), which is a measure of the fractional quantity of the product recovered after the purification. We demonstrate that the purity of SWNTs significantly affects their mechanical and electrical properties.

Knudsen layer losses of tail fuel ions can significantly reduce the fusion reactivity of multi-keV DT in capsules with small fuel ρr; sizable yield reduction can result for small inertial confinement fusion (ICF) capsules. This effect is most pronounced when the distance from a burning DT gas region to a nonreacting or cold wall is comparable to the mean free path of reacting fuel ions. A simplified asymptotic theory of Knudsen layer tail depletion is presented and a nonlocal reduced fusion reactivity model is obtained. Application of the model in simulations of ICF capsule implosion experiments gives calculated yields and ion temperatures that are in much closer agreement with observations than are the results of "nominal" or mixed simulations omitting the model.

A three-dimensional magnetohydrodynamic code has been used to study the nonlinear evolution of the tilt instability in a field-reversed configuration. The evolution of the mode has been followed through magnetic field reconnection to complete the loss of confinement, with no evidence of any nonlinear stabilizing effects. The influence of plasma rotation has also been investigated. It was found that while the mode remains unstable, its character changed at high rotation rates. It evolves from an internal mode with a very small displacement velocity at the separatrix, to an external mode with almost no radial component to the displacement velocity. Hall term effects were found to be capable of reducing the growth rate for small and elongated configurations, but again, a change in mode character was found to prevent the stabilization predicted in a previous analysis. Kinetic effects remain the most promising mechanism to explain the observed stability of current experiments.

Electron energy transport in field reversed configuration (FRC) equilibria is studied experimentally for a variety of conditions. Up to 37% of the global plasma power loss is attributed to non-convective processes by electrons. The electron temperatures are approximately two times larger than those measured without reversed bias field, which indicates confinement by the poloidal magnetic field in the FRC. The inferred average cross-field thermal diffusivities χ⊥e are anomalous, ranging between 35 and 140 times classical, and are consistent with transport from turbulent magnetic fluctuations of 1 to 2%.

A two-dimensional kinetic description of field-reversed equilibria has been developed. Three equilibrium models are presented: a kinetic model, a rigidly rotating model, and a magnetohydrodynamics (MHD) model. The kinetic model of equilibrium provides spatial distributions of the macroscopic moments, including velocity shear, that are in good agreement with experimental observations. The rigidly rotating and MHD models allow more general pressure profiles than previous studies. These models, which allow the computation of a wide range of equilibria, suggest that for parameters typical of the current experiments kinetic modifications of the equilibrium are small; however, they may be important if the field-reversed configuration is interacting strongly with a magnetic mirror. Also, the ability to compute kinetic equilibria makes possible a self-consistent examination of the stability of field-reversed configurations, which is believed to be strongly influenced by kinetic effects.