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From the nonlinear simulations of the two-dimensional forced-damped Hasegawa-Mima equation, we show that a Reynolds number-like parameter, Rew, can represent a power law exponent of the energy spectrum in Hasegawa-Mima turbulence. Rew is defined as the ratio of nonlinear convection to dissipation. For a same value of Rew, the power law exponent in the inertial range is shown to be uniquely determined regardless of the forcing and dissipation conditions. At high Rew, the power law exponent asymptotically converges to -7.2, consistent with a recent theoretical prediction based on the shell model [Gürcan et al., Plasma Phys. Controlled Fusion 52, 045002 (2010)]. [ABSTRACT FROM AUTHOR]

Numerical studies are made of the effects of resistivity on linear plasma responses to resonant magnetic perturbations (RMPs) in tokamaks based on a reduced magnetohydrodynamic model. From a local two-field model, it is suggested that the ratio of the poloidal electron advection to the resistivity diffusion rate αmαm can be a figure of merit parameter in linear RMP penetration physics. The shielding efficiency is governed by αm, and when αm ≳ 1, RMPs are effectively shielded. Global simulations using a four-field model [Hazeltine and Meiss, Phys. Rep. 121, 1 (1985)] show that there exists an effective threshold of the perpendicular electron flow (Ve,⊥c) beyond which RMPs cannot penetrate. Resistivity is found to determine Ve,⊥c which increases as resistivity becomes higher, making RMP penetration easier. At low resistivity, small Ve,⊥c renders the RMP penetration sensitive to ion collisionality and the change in q 95. The kink response is observed to be closely related to the residual level of RMPs at rational surfaces and can be also strongly affected by resistivity. [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]

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]

A theoretical study is made of the effects of radio frequency (rf) waves in the range of ion cyclotron frequency on interchange modes in mirror plasmas. A two-fluid cold plasma model including particle collisions is utilized for the investigation. Both the equilibrium ponderomotive force produced by the gradient of rf wave amplitude and the sideband wave coupling mechanism originated from the nonlinear beating between high frequency waves are taken into account. A tractable form of the dispersion relation for the interchange mode is obtained and applied to carrying out a parametric study. Key parameters affecting the stability boundary are identified and the consequences of the parameter variation on the stability boundary change are analyzed near ion cyclotron resonance region. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]