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From nonlinear flux-driven fluid simulations, we show that the external torque has a profound influence on ion thermal confinement. A key parameter controlling the confinement change is found to be the ratio of the net external torque to the applied power input. For a given value of external torque, the ion temperature profile destiffening and the corresponding confinement enhancement occur when the ratio is below a threshold value. This confinement improvement is shown to originate from the increase in the zonal flow shearing rate due to the conversion of parallel flow compressibility to zonal vorticity. Confinement degradation and the restoration of profile stiffness arise beyond the critical value of the ratio due to the onset of the parallel velocity gradient instability. This result implies the existence of an optimal torque value for the given heating power to maximize the thermal confinement. [ABSTRACT FROM AUTHOR]

ThO(cr) was dissolved in the solutions containing various carbonate ion concentrations, and the results were compared with thorium solubility in a domestic granitic groundwater having very low ionic strength. The soluble thorium concentration excluding colloids after phase separation increased with increasing carbonate concentration. However, the thorium concentration in the real groundwater was remarkably greater than that in the carbonate-containing solutions with a similar concentration of carbonate and pH condition. This might be attributable to other species as well as Th(OH)(aq) and Th(OH)(CO). These species form colloids or precipitates, and their concentration can be reduced in the ultra-filtered solution by an aging effect. [ABSTRACT FROM AUTHOR]

The solubilities of NpO2(s) in the KURT (KAERI Underground Research Tunnel) granitic groundwater with low ionic strength were measured experimentally and calculated by a geochemical code. Then these results were compared with each other as well as with foreign results. The concentrations of neptunium were measured as 6·10−8−2·10−8 mol/L at a pH = 9.5–11.1 and Eh = −0.2 V, and less than 5·10−9 mol/L at a pH = 11.8–13.0 and Eh = −0.3–0.44 V. The dominant aqueous species were presumed as Np(OH)x(CO3)y 4−x−2y complexes and Np(OH)4(aq) at pH = 9.5–13 under the Eh<−0.2 V reducing condition. [ABSTRACT FROM AUTHOR]

A simplified two-dimensional Monte Carlo simulation is performed to estimate the charging potential fluctuations caused by strong binary Coulomb interactions between discrete charged particles in nanometer scale trenches. It is found that the discrete charge effect can be an important part of the nanoscale trench research, inducing scattering of ion trajectories in a nanoscale trench by a fluctuating electric field. The effect can enhance the ion deposition on the side walls and disperse the material contact energy of the incident ions, among others. [ABSTRACT FROM AUTHOR]

The analytic solution for the time stationary non-monotonic double layers in multi-species plasma is presented. This solution is the analytic extension of the monotonic double layer and the solitary hole. We have derived the modified Korteweg–de Vries equation in plasmas, taking account of negative ion effects. The effects of negative ion and density on the properties of the non-monotonic double layer are discussed. [ABSTRACT FROM PUBLISHER]

A method to control negative ion density in SF6/Ar capacitive discharges with a biased grid is proposed. It is observed that the negative ion density and its ratio to positive ion density are variable in a wide range from 2.8×107 to 4×109 cm-3 and from 0.18 to 0.86, respectively, depending on the grid bias voltage. To investigate the effect of grid bias on negative ion generation, electron energy distribution functions (EEDFs) are measured and rate constants for electron attachment reactions are calculated at various bias voltages. Results are shown that the attachment processes are predominantly governed by the fraction of low energy electrons in the EEDF, which is controllable using the grid bias. [ABSTRACT FROM AUTHOR]

Recently, electrokinetic injection has been applied in bioremediation to provide nutrients and TEAs in low permeable soil. However, an effective pH control system and a uniform injection system have yet to be developed. This study investigated an enhanced EK injection system, which is combined with electrolyte circulation and electrode polarity reversal on kaolinite. Soil pH was maintained continuously only by circulation of electrolytes in each chamber without any buffering solutions. Existing ions were distributed more uniformly in soil by electrode polarity reversal. In view of microbiological degradation, the polarity reversal system resulted in better ion injection. Therefore, the novel electrokinetic nutrient and TEAs injection system can be applied to in situ biodegradation more effectively than the conventional technique. [ABSTRACT FROM AUTHOR]

A study on the dependence of electron energy distribution function (EEDF) on discharge gap size in capacitive rf discharges was conducted. The evolution of the EEDF over a gap size range from 2.5 to 7 cm in 65 mTorr Ar discharges was investigated both experimentally and theoretically. The measured EEDFs exhibited typical bi-Maxwellian forms with low energy electron groups. A significant depletion in the low energy portion of the bi-Maxwellian was found with decreasing gap size. The results show that electron heating by bulk electric fields, which is the main heating process of the low-energy electrons, is greatly enhanced as the gap size decreases, resulting in the abrupt change of the EEDF. The calculated EEDFs based on nonlocal kinetic theory are in good agreement with the experiments. [ABSTRACT FROM AUTHOR]

In a modern plasma etching device, the plasma sheath potential is usually superposed by an externally driven oscillating voltage to enhance and control the bombarding ion energy. A collisionless particle simulation is used to study the variation of average kinetic energy (ν[sub rf]) of bombarding ions as a function of a wide range of sheath oscillation frequency ν[sub rf] (0.1ν[sub pi]≼ν[sub rf]≼10ν[sub pi], where ν[sub pi] is the ion plasma frequency). It is found that a resonance phenomenon between the ion transit motion and the sheath oscillation can yield a strongly peaked enhancement of (ν[sub rf]) near ν[sub rf]=0.5ν[sub pi]. Ion species with different mass show the peaks at different ν[sub rf]. The relative importance of different ion molecules in an ion-enhanced etching process will be sensitive to ν[sub rf]. This phenomenon may allow a reduction of the undesirable capacitive coupling by optimizing ν[sub rf] to yield an enhanced of desired ion species at low applied voltages. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]