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In this paper, a theoretical model is described and demonstrated that serves as a useful tool for understanding K-shell radiating Z-pinch plasma behavior. Such understanding requires a self-consistent solution to the complete nonlocal thermodynamic equilibrium kinetics and radiation transport in order to realistically model opacity effects and the high-temperature state of the plasma. For this purpose, we have incorporated into the MACH2 two-dimensional magnetohydrodynamic (MHD) code [R. E. Peterkin et al., J. Comput. Phys. 140, 148 (1998)] an equation of state, called the tabular collisional radiative equilibrium (TCRE) model [J. W. Thornhill et al., Phys. Plasmas 8, 3480 (2001)], that provides reasonable approximations to the plasma’s opacity state. MACH2 with TCRE is applied toward analyzing the multidimensional implosion behavior that occurred in Decade Quad (DQ) [D. Price et al., Proceedings of the 12th IEEE Pulsed Power Conference, Monterey, CA, edited by C. Stallings and H. Kirbie (IEEE, New York, 1999), p. 489] argon gas puff experiments that employed a 12 cm diameter nozzle with and without a central gas jet on axis. Typical peak drive currents and implosion times in these experiments were ∼6 MA and ∼230 ns. By using Planar Laser Induced Fluorescence measured initial density profiles as input to the calculations, the effect these profiles have on the ability of the pinch to efficiently produce K-shell emission can be analyzed with this combined radiation-MHD model. The calculated results are in agreement with the experimental result that the DQ central-jet configuration is superior to the no-central-jet experiment in terms of producing more K-shell emission. These theoretical results support the contention that the improved operation of the central-jet nozzle is due to the better suppression of instabilities and the higher-density K-shell radiating conditions that the central-jet configuration promotes. When we applied the model toward projecting argon K-shell yield behavior for Sandia National Laboratories’ ZR machine (∼25 MA peak drive currents, ∼100 ns implosion times) [D. McDaniel et al., Proceedings of the 5th International Conference on Dense Z-Pinches, Albuquerque, NM, 2002, edited by J. Davis, C. Deeney, and N. R. Pereira (American Institute of Physics, New York, 2002), Vol. 651, p. 23] for experiments that utilize the 12 cm diameter central-jet nozzle configuration, it predicts over 1 MJ of K-shell emission is attainable. [ABSTRACT FROM AUTHOR]

Using the quantum hydrodynamic model, quantum dust ion-acoustic solitary waves are investigated in the presence of weak transverse perturbations. The linear dispersion relation is obtained using the Fourier analysis. The two-dimensional (2D) propagation of small amplitude nonlinear waves is studied by deriving the Kadomtsev–Petviashvili (KP) equation. The traveling wave solution of the KP equation is obtained by employing the tanh method. By dint of this solution, the effects of quantum Bohm pressure and the dust concentration on the 2D solitary structure are studied. The effect of quantum Bohm potential on the stability of the KP soliton is also investigated. The results are supported by the numerical analysis and the relevance of the present investigation in dense astrophysical environments is also pointed out. [ABSTRACT FROM AUTHOR]

Acceleration and heating of a relativistic electron beam due to nonlinear electron Landau and cyclotron damping of electromagnetic waves in a magnetized plasma are investigated theoretically and numerically on the basis of the relativistic kinetic wave and transport equations derived from the relativistic Vlasov–Maxwell equations. Two electromagnetic waves interact nonlinearly with the relativistic electron beam, satisfying the resonance condition of ωk-ωk′-(k⊥-k⊥′)vd-(k|-k|′)vb≃mωce, where vb and vd are the parallel and perpendicular velocities of the relativistic electron beam, respectively, and ωce is the relativistic electron cyclotron frequency for the electron beam. The beat waves whose frequency is near the frequency of the extraordinary wave are excited by two electromagnetic waves. The beat waves resonate with the relativistic electron beam and accelerate efficiently. Nonlinear electron Landau and cyclotron damping of the electromagnetic waves has been studied by the numerical analysis of the relativistic nonlinear wave-particle coupling coefficients, assuming the relativistic electron beam with the relativistic drifted Maxwellian momentum distribution without the cross-field drift (vd=0), and it was verified that the highly relativistic electron beam with the energy of βmec2≲5 TeV can be accelerated efficiently by the Compton scattering and the beat-wave excited extraordinary waves, where β=(1-vb2/c2)-1/2. For comparison, the equations of motion for the beam electrons trapped in the beat wave in the frame of reference moving with vb are analyzed. The detailed acceleration mechanism was clarified and the qualitative agreement with the numerical results was obtained. [ABSTRACT FROM AUTHOR]

The ellipticity criteria for the partial differential equations of axisymmetric single-fluid and Hall magnetohydrodynamic (MHD) equilibria with flow and pressure anisotropy are investigated. The MHD systems are closed with cold ions and electron pressures derived from their parallel heat flux equations, a closure that reproduces the corresponding kinetic dispersion relation. In the single-fluid model, which differs from the double-adiabatic Chew–Goldberger–Low model, it is verified that the elliptic region boundaries occur at poloidal flow velocities equal to wave velocities from the kinetic dispersion relation. For Hall magnetohydrodynamics, a set of anisotropic-pressure equilibrium equations is derived and an ellipticity condition corresponding to a poloidal flow velocity slightly smaller than the ion sound velocity is obtained. [ABSTRACT FROM AUTHOR]

The Columbia Non-neutral Torus (CNT) [T. S. Pedersen, J. P. Kremer, R. G. Lefrancois, Q. Marksteiner, N. Pomphrey, W. Reiersen, F. Dahlgreen, and X. Sarasola, Fusion Sci. Technol. 50, 372 (2006)] is a stellarator used to study non-neutral plasmas confined on magnetic surfaces. A detailed experimental study of confinement of pure electron plasmas in CNT is described here. Electrons are introduced into the magnetic surfaces by placing a biased thermionic emitter on the magnetic axis. As reported previously, the insulated rods holding this and other emitter filaments contribute to the radial transport by charging up negatively and creating E×B convective transport cells. A model for the rod-driven transport is presented and compared to the measured transport rates under a number of different conditions, finding good agreement. Neutrals also drive transport, and by varying the neutral pressure in the experiment, the effects of rod-driven and neutral-driven transport are separated. The neutral-driven electron loss rate scales linearly with neutral pressure. The neutral driven transport, presumably caused by electron-neutral collisions, is much greater than theoretical estimates for neoclassical diffusion in a classical stellarator with strong radial electric fields. In fact the confinement time is on the order of the electron-neutral collision time. Ion accumulation, electron attachment, and other effects are considered, but do not explain the observed transport rates. [ABSTRACT FROM AUTHOR]

The results of a hybrid numerical simulation of the growth kinetics of carbon nanowall-like nanostructures in the plasma and neutral gas synthesis processes are presented. The low-temperature plasma-based process was found to have a significant advantage over the purely neutral flux deposition in providing the uniform size distribution of the nanostructures. It is shown that the nanowall width uniformity is the best (square deviations not exceeding 1.05) in high-density plasmas of 3.0×1018 m-3, worsens in lower-density plasmas (up to 1.5 in 1.0×1017 m-3 plasmas), and is the worst (up to 1.9) in the neutral gas-based process. This effect has been attributed to the focusing of ion fluxes by irregular electric field in the vicinity of plasma-grown nanostructures on substrate biased with -20 V potential, and differences in the two-dimensional adatom diffusion fluxes in the plasma and neutral gas-based processes. The results of our numerical simulations are consistent with the available experimental reports on the effect of the plasma process parameters on the sizes and shapes of relevant nanostructures. [ABSTRACT FROM AUTHOR]

The effect of an oscillating sheath on near-wall conductivity has been studied using a model of the incident electron motions with the characteristic parameters of the oscillating sheath quantified. The model predicted an increase in both the frequency of electron-wall collisions and the coefficient of secondary electron emission compared to the steady sheath regime. This effect indicates that near-wall conductivity is enhanced in the oscillating sheath regime. [ABSTRACT FROM AUTHOR]

Nonlinear simulations based on the magnetohydrodynamic model have been executed to reveal the dynamics of the ballooning mode in the spherical tokamak plasma. The simulation results have reproduced the characteristic features of the edge-localized mode crash phase, where the filamentary structures are formed along the magnetic field in the edge region, and separated from the core plasma. Moreover, the finite Larmor radius effect is addressed. [ABSTRACT FROM AUTHOR]

The Coulomb contribution to the electrical conductivity of partially ionized plasmas is discussed and its general behavior is investigated. Recent experiments on the direct current conductivity in shock wave induced argon and xenon plasmas are analyzed in this context. Within the relaxation time approach, the Coulomb contribution is extracted by eliminating the contribution of scattering from neutrals. Alternatively, the Coulomb contribution can be calculated directly within linear-response theory. In particular, from the latter approach a generalized Spitzer factor is derived for taking into account electron-electron interactions within the relaxation time approximation. Experimental results for the Coulomb contribution to the electrical conductivity are in reasonable agreement with an interpolation formula derived from linear-response theory. [ABSTRACT FROM AUTHOR]

The nonlinear evolution of three-dimensional reconnection instabilities are studied in a current sheet where many resonant surfaces are simultaneously present at different locations of the simulation domain. The nonlinear evolution produces the development of anisotropic magnetohydrodynamic turbulence. The development of the energy spectrum is followed until the energy is transported to the dissipative length scale and the anisotropy of the spectrum is analyzed. The energy cascade is affected by the Alfvén effect and it takes place mainly in the direction perpendicular to the local average magnetic field. Anisotropy is also affected by propagation of perturbations across the main magnetic field, due to the growth of a transverse component related to reconnection. The direction of anisotropy varies with the position in space. The spectral index is different both from what is found in homogeneous isotropic turbulence and from the values predicted for magnetohydrodynamic turbulence with a uniform large-scale magnetic field. [ABSTRACT FROM AUTHOR]

A simple theoretical model is developed which describes how current eddies are excited in the scrape-off layer (SOL) of a large-aspect-ratio, low-β, circular cross-section tokamak by time-varying magnetohydrodynamical instabilities originating from within the plasma. This model is used to study the interaction of SOL currents with tearing modes and resistive wall modes in a typical tokamak plasma. SOL currents are found to be fairly effective at braking the rotation of tearing modes, and to have a significant destabilizing effect on resistive wall modes. [ABSTRACT FROM AUTHOR]

The Ni-like Ag x-ray laser at 13.9 nm (4d→4p, J=0→1) is numerically studied, using a one-dimensional hydrodynamic code coupled with an atomic physics code. The effects of the drive laser intensity, pulse duration, and delay time on the performance of the Ni-like Ag x-ray laser are investigated. A saturated x-ray laser output could possibly be generated for a short plasma length under the optimized drive pulse configuration. The analysis of the plasma conditions, including the evolution of gain in time and space, the electron temperature and the electron density, contribute to further understanding of the process of Ni-like x-ray lasers. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]