ISSN:1070-664X    

DOI:10.1063/1.3480127

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Measurements of edge plasma turbulence properties have been carried out in the Advanced Toroidal Facility (ATF) [Fusion Technol.10, 179 (1986)] during experiments in which hydrogen and neon gas puffing are used to vary the edge temperature in the range 5<Te<40 eV in a controlled way. In the temperature range where the rate coefficients for ionization processes are strongly temperature dependent (5<Te<15 eV) the electron temperature plays an important role in determining the level of edge turbulence and the value of the self‐generated radial electric fields. These results provide evidence of edge turbulence and flows modified by the presence of neutral particles.

ISSN:1070-664X    

DOI:10.1063/1.870556

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The geometric optics approximation is the commonly used description for wave propagation in media where the usual local Wentzel–Kramers–Brillouin (WKB) condition is satisfied. However, diffraction phenomena can give important corrections to a ray trajectory and scattering description when focused waves are launched. The general mathematical description for such electromagnetic beams is formulated for a general magnetized plasma and shown to be of a simple functional form. For propagation perpendicular to the magnetic field in a cold plasma the equations are shown to be particularly simple and specifically demonstrate the importance of retaining anisotropic plasma effects for focused beam experiments. In an equilibrium plasma with a particular class of RF boundary conditions the general functional form is shown to be solvable analytically and the solutions expressed in terms of solutions of the ray approximation.

ISSN:1070-664X    

DOI:10.1063/1.870560

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A (2d,3v), electrostatic, collisionless kinetic slab model for a wide class of negative‐bias dc states of the single‐ended Q machine is developed. The self‐consistent plasma state is found by means of an iterative scheme in which the charge‐density and potential distributions are alternately advanced. The electron and ion velocity distribution functions are calculated via trajectory integration, which ensures high accuracy and resolution in both configuration and velocity spaces. As compared to similar previous schemes, this ‘‘trajectory‐simulation’’ method exhibits some modifications, significantly reducing computing time and enhancing numerical stability, so that it is also applicable to ‘‘long’’ systems (≥102Debye lengths). Macroscopic quantities as well as velocity distribution functions for two exemplary special cases are systematically presented. To the authors’ knowledge, these results represent the most comprehensive and detailed kinetic analysis of any bounded plasma system given so far.

ISSN:1070-664X    

DOI:10.1063/1.870544

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

When in a double plasma machine (DP‐machine) plasma is produced solely in the source chamber, not only ions but also electrons can leak through the separating grid into the target chamber, so that a low‐density plasma forms there. The electrons are trapped by the traveling ion space charge and can thereby overcome the strongly negative grid bias. The investigations presented here show that a positive space‐charge forms behind the grid in the target chamber and a deep potential well is formed around the grid. When the anode of the target chamber is biased positively, under certain conditions a low‐frequency instability is observed in the target chamber, the properties of which indicate a potential relaxation oscillation, somewhat similar to the potential relaxation instability in a quiescent plasma machine (Q machine). The frequency of the instability is determined by the ion transit time through a thin layer of the target chamber plasma. In addition, resonant coupling occurs between this frequency and the bounce frequency of ions in the potential well around the grid.

ISSN:1070-664X    

DOI:10.1063/1.870555

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The theory of resistive dissipation of linear compressible modes in a nonuniform plasma is presented in a unified way, following a normal mode approach. The familiar modes of a homogeneous ideal plasma are shown to be substantially modified by the presence of the resistivity and nonuniformity. It is then argued that the most suitable criterion for mode identification is based on the asymptotic properties of the solutions. The modes are then classified as ideal or resistive according to the asymptotic absence or presence of the resistivity. After a brief summary of the results from previous articles, made for the sake of completeness, the article concentrates on the new results concerning the compressible ideal solutions, the only ones that exhibit a resonant behavior. The properties of the solutions are examined by treating an explicit example of a nonhomogeneous situation. It is shown that the nature of the modes varies in the direction of nonuniformity, being essentially a fast mode in the asymptotic region, a slow mode in the vicinity of the so‐called cusp resonance, and an Alfve´nic mode near the Alfve´nic resonance point.

ISSN:1070-664X    

DOI:10.1063/1.870557

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The off‐axis quasilinear fast wave minority heating description of Catto and Myra [Phys. Fluids B4, 187 (1992)] has been improved and implemented in a code which solves the combined quasilinear and collision operator equation for the minority distribution function. Geometrical complications of a minority resonance nearly tangent to a flux surface in the presence of trapped as well as passing particles are retained. The tangency interactions alter the moments and the fusion reaction rate parameter in a model which explores heating on a single flux surface. The strong tangency interactions enhance the more familiar interactions due to trapped particles turning in the vicinity of the minority resonance. An asymmetry in off‐axis heating effects occurs because heating on the low field side of the magnetic axis heats more trapped particles than high field side heating. This asymmetry is responsible for the better performance of the low field side case relative to the high and on‐axis cases and provides some control over the power absorbed by and the energy stored in the trapped particles.  

ISSN:1070-664X    

DOI:10.1063/1.870558

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The effect of the background drift wave turbulence on the evolution of the low‐mtearing modes has been studied, in the quasilinear regime, in various limiting cases. It is found, in the cases of them=1 classical, collisionless, and drift‐tearing modes, that the turbulence introduces finite real frequencies to these modes, which are otherwise purely growing ones, but reduces their instability activity. In the case of them≥2 classical modes, in a limit ‖&agr;‖1/2≫&rgr;i, the turbulence enhances the frequencies as well as the growth rates of these modes; and in the case of them≥2 collisionless modes, in the same limit, it enhances the frequencies of these modes, but reduces their instability activity, where ‖&agr;‖1/2is the current channel width and &rgr;iis the ion Larmor radius.  

ISSN:1070-664X    

DOI:10.1063/1.870559

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The stability of oblique modulation of ion‐acoustic waves in a collisionless plasma consisting of two cold‐ion species with different masses, concentrations, and charge states, and hot isothermal electrons is studied. Using the Krylov–Bogoliubov–Mitropolosky (KBM) perturbation technique, a nonlinear Schro¨dinger equation governing the slow modulation of the wave amplitude, is derived for the system. It is found that the presence of second‐ion species significantly changes the instability domain in thek‐&fgr; plane. The effect of charge state, concentration, and mass of second‐ion species on the modulational instability is discussed in detail. The predictions of the theory are found to be in good agreement with the experimental observations.

ISSN:1070-664X    

DOI:10.1063/1.870561

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In this article, a new emission process for radiation near the plasma frequency in an unmagnetized plasma (i.e., the plasma emission) is discussed. The process involves a tenuous beam of energetic electrons and low‐frequency ion waves. The key point is that the ion waves can modulate the thermal electron density so that the condition for beam–plasma interaction (&ohgr;=k⋅V, whereVis the average beam velocity) is Doppler shifted in wave vector space in accordance with the wavelength that characterizes the ion density fluctuations [&ohgr;+&ohgr;’=(k+k’)⋅V, where &ohgr;’andk’are the characteristic frequency and wave vector associated with the ion wave; in the present discussion, let set &ohgr;’=0]. As a result, the unstable electrostatic beam–plasma mode becomes coupled with the fast electromagnetic mode. Consequently in an inhomogeneous plasma the amplified waves can naturally change to electromagnetic mode and escape from the source region.

ISSN:1070-664X    

DOI:10.1063/1.870463

出版商:AIP    

年代:1994

数据来源: AIP