Vol 44, No 3 (2018)

Braginskii reduced equations of two-fluid hydrodynamics are modified to take into account the presence of an external ac electric field localized in the tokamak near-wall layer. Numerical simulations show that, after reaching certain amplitude, such a field oscillating with the frequency ω ≈ ω_GAM is capable of suppressing turbulent processes. The turbulence suppression mechanism consists in a sharp decrease in the growth rate of drift-resistive ballooning instability due to the appearance of additional nonlinear terms related to the external field in the equation for the vorticity.

Generation of terahertz waves by hot dense plasma under the action of a femtosecond laser pulse in the regime of anomalous skin effect is considered. The spectral, angular, and energy characteristics of terahertz waves are studied as functions of the plasma and laser parameters. It is shown that, under the conditions of anomalous skin effect, which takes place in ultradense hot plasma, the total energy of the terahertz signal is independent of the electron density, proportional to the square of the electron temperature, and maximal at tight focusing of the laser pulse.

The gravito-electrostatic sheath (GES) model, previously proposed to address the fundamental issues on the surface emission mechanism of outflowing solar plasma on the basis of plasma−wall interaction processes with inertialess electrons on both bounded and unbounded scales, is reformulated in the light of active electron inertial response amid geometrical curvature effects. We accordingly derive the electron population distribution law considering both weak electron inertia and geometrical curvature effects in a new analytic construct coupled with the GES structure equations in a closed form. The analysis shows that the GES characteristics and hence plasma outflow dynamics are noticeably affected because of electron inertia. As a consequence of the electron inertia inclusion in contrast with the previous GES formalism, it is found that the GES width gets reduced (–5%), the sheath boundary gets contracted (–7%), the net current density at the surface gets reduced (–25%), the GES potential enhances (+17%), the transonic horizon decreases (‒35%), self-gravity enhances (+2%), and so forth. The obtained results are in fair accord with the existing model predictions centered around both the earlier GES formalisms and standard fluid-kinetic predictions.

The memory effect (the dependence of the dynamic breakdown voltage U_b on the time interval τ between voltage pulses) in pulse-periodic discharges in pure argon and the Ar + 1%N₂ mixture was studied experimentally. The discharge was ignited in a 2.8-cm-diameter tube with an interelectrode distance of 75 cm. The measurements were performed at gas pressures of P = 1, 2, and 5 Torr and discharge currents in a steady stage of the discharge of I = 20 and 56 mA. Breakdown was produced by applying positive-polarity voltage pulses, the time interval between pulses being in the range of τ = 0.5–40 ms. In this range of τ values, a local maximum (the anomalous memory effect) was observed in the dependence U_b(τ). It is shown that addition of nitrogen to argon substantially narrows the range of τ values at which this effect takes place. To analyze the measurement results, the plasma parameters in a steady-state discharge (in both pure argon and the Ar + 1%N₂ mixture) and its afterglow were calculated for the given experimental conditions. Analysis of the experimental data shows that the influence of the nitrogen admixture on the shape of the dependence U_b(τ) is, to a large extent, caused by the change in the decay rate of the argon afterglow plasma in the presence of a nitrogen admixture.

The effect of the shape of the feeding voltage on the spatiotemporal characteristics of an atmospheric- pressure barrier microdischarge in argon is demonstrated using numerical simulations based on an extended fluid model. Results of simulations performed for sinusoidal and square feeding voltages are analyzed.

Tri-Alpha and Helion energy companies have proposed an approach as the near future fusion reactor. The method used in this kind of reactor for attaining high fusion yield is based on the formation and throwing of two plasmoids toward each other. In this study, the optimized reaction rate for interpenetration of two head on colliding plasmoids is investigated. Calculations are performed by supposing the velocity of plasmoids ions as Maxwellian distribution function. Fusion output-to-input power ratio (Q factor) was computed by evaluation of the velocity-averaged cross sections and also ion−electron and ion−ion Coulomb power loss. A fluid model including a computational code has been used for the precise calculations of fusion power balance. The optimum interpenetration velocity and plasmoids parameters required to reach the ignition are studied for aneutronic fusion fuels, such as p–¹¹B and D–³He, as well as D−T and D−D fuels. The results of investigation show that the breakeven is attainable in specific collision velocity and plasma temperature for each fuel. Also, the plasma density has to be around 10²⁰ ions/cm³.