摘要:

The bispectrum is used to demonstrate that wave–wave coupling occurs when ponderomotive forces due to wave fields in the ion cyclotron range of frequencies are used to stabilize a magnetized plasma column against magnetohydrodynamic (MHD) interchange instabilities. The three waves that interact resonantly are an applied wave, a MHD wave, and the nonlinearly coupled sideband wave. The net ponderomotive forces contain partially canceling and augmenting contributions from each induced sideband field.

ISSN:0899-8221    

DOI:10.1063/1.859192

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Resonance cones are studied experimentally in hot drifting plasmas and in various beam–plasma situations. In a drifting plasma the upstream–downstream asymmetry of the main cone is suitable for diagnostics of plasma drifts. The evaluation of electron temperature from the interference pattern is discussed in terms of the low‐temperature–low‐drift approximation (LTLDA) and by comparing with numerical kinetic theory calculations. In this way the range of applicability of this method is extended above the LTLDA. In a beam–plasma situation, the downstream resonance cone exhibits a new interference pattern, which can be attributed to resonant particle effects. The upstream resonance cone is only slightly affected and is found still applicable forTeandnediagnostics. As a result of comparison with numerical calculations, in which the actual distribution function is used, the downstream interference pattern is proposed to be useful as a diagnostic method for obtaining the mean beam energy. The waves generated by the beam–plasma interaction are analyzed by digital cross‐correlation techniques, and found to propagate obliquely to the magnetic field direction at the resonance cone angle.

ISSN:0899-8221    

DOI:10.1063/1.859193

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

One‐dimensional three‐wave models, known for stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS), are investigated. It is shown that in homogeneous systems of infinite extent the steady‐state three‐wave solution for SBS with a reflectivity less than 100% is intrinsically unstable. From a numerical solution it is concluded that nearly all stationary states decay in time and result in a state with reflectivity coefficientR=1; only the latter is linearly stable in a homogeneous plasma of infinite length. The asymptotic solutions for SBS in plasmas are calculated and the similarity in the dynamics between SBS and SRS is discussed.

ISSN:0899-8221    

DOI:10.1063/1.859194

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The dissipative trapped ion instability (DTII) is observed as anm=1 mode localized to the mirror cell of the Columbia Linear Machine (CLM) [Plasma Phys.24, 185 (1982)]. A gated feedback diagnostic allows the direct measurement of the DTII linear growth rate. The DTII growth rate is measured as a function of trapped fraction, keeping all other parameters fixed, and clearly displays the scaling with trapped fraction predicted by the radially local linear dispersion relation, including ion Landau damping. The saturated DTII mode amplitude is measured concurrently with the growth rate. The saturated amplitude displays a nearly linear dependence on the measured growth rate, normalized to the DTII real frequency, and is nearly proportional to the square root of the measured growth rate. A striped particle collector is used to measure the ambipolar radial plasma flux as the trapped fraction is varied. Radial diffusion coefficients are calculated from the measured radial particle fluxes and display a scaling intermediate between the Kadomtsev weak and strong turbulence predictions.

ISSN:0899-8221    

DOI:10.1063/1.859195

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Starting from the Fokker–Planck or Boltzmann type of linearized kinetic equation, and using a projection operator technique, a general evolution equation is derived for the hydrodynamical component of the distribution function with a renormalized collision operator providing extra dissipation mechanisms. Generalized Fourier and Newtonian laws are derived leading to nonlocal transport in time and space. Explicit evaluation of the transport coefficients is performed after a discussion of various truncation procedures. The results are applied to the study of dispersion and damping of sound in a rarefied one‐component gas. A comparison with experimental results shows that a 14‐moment approximation is very satisfactory.

ISSN:0899-8221    

DOI:10.1063/1.859143

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Generalized hydrodynamical equations are derived for a nonequilibrium plasma characterized by different temperatures and velocities for the electrons and ions. Their conductivities and viscosities appear to be inhibited by supplementary dissipation mechanisms caused by the inhomogeneities of the system. These modifications have profound implications for the properties of propagation and damping of ion‐acoustic waves in the system.

ISSN:0899-8221    

DOI:10.1063/1.859144

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Simulation of the kinetic Alfve´n wave is performed using a two‐and‐one‐half‐dimensional (2 (1)/(2) ‐D) macroscale particle [magnetohydrodynamic (MHD) scale kinetic] simulation code. An oscillating antenna current is applied in one of the boundary regions to launch MHD perturbations into an inhomogeneous plasma in which a sheared magnetic field is present. It is shown that the applied perturbation is mode converted into the kinetic Alfve´n wave at the Alfve´n resonance layers, resulting in resonant heating of both the ions and electrons. When the plasma beta is relatively low, only the electrons are heated along the ambient magnetic field. The electron heating rate is found to be scaled asdTe∥/dt∝&bgr;1/2e⟨&dgr;B2y⟩, where &bgr;eis the electron beta and ⟨&dgr;B2y⟩ is the wave magnetic field intensity. In contrast, ion heating occurs when the ion beta is close to unity and the temperature ratio satisfiesTe/Ti>1. Besides plasma heating, it is found that the plasma particles are accelerated along the ambient magnetic field in the direction of the wave propagation through Landau resonance with the kinetic Alfve´n wave.

ISSN:0899-8221    

DOI:10.1063/1.859145

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

An approximate normal mode analysis of plasma current diffusion in tokamaks is presented. The work is based on numerical solutions of the current diffusion equation in cylindrical geometry. Eigenvalues and eigenfunctions are shown for a broad range of plasma conductivity profile shapes. Three classes of solutions are considered that correspond to three types of tokamak operation. Convenient approximations to the three lowest eigenvalues in each class are presented, and simple formulas for the current relaxation time scales are given and applied to several cases of simple current relaxation as well as noninductive current drive. Simulations of current relaxation with and without current redistribution caused by a ‘‘sawtooth’’ model show that sawteeth can considerably shorten the relaxation time if the sawtooth region extends tor∼a/2.

ISSN:0899-8221    

DOI:10.1063/1.859146

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The derivation of the wave equation that governs ion cyclotron range of frequencies (ICRF) wave propagation, absorption, and mode conversion within the kinetic layer in tokamaks has been extended to include diffraction and focusing effects associated with the finite transverse dimensions of the incident wave fronts. The kinetic layer considered consists of a uniform density, uniform temperature slab model in which the equilibrium magnetic field is oriented in thezˆ direction and varies linearly in thexˆ direction. An equivalent dielectric tensor, as well as a two‐dimensional energy conservation equation, are derived from the linearized Vlasov–Maxwell system of equations. A generalized, but approximate form of the mode conversion‐tunneling equation is then extracted from the Maxwell equations, using the parabolic approximation method in which transverse variations of the wave fields are assumed to be weak in comparison to the variations in the primary direction of propagation. Numerical solutions of this approximate wave equation agree well with solutions to the exact wave equation within the kinetic layer.

ISSN:0899-8221    

DOI:10.1063/1.859208

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Recent work on fast‐wave propagation in the ion cyclotron range of frequencies has shown that the fast‐wave transmission and reflection coefficients can be obtained from a second‐order equation in which the ion Bernstein mode is treated as a driven response to the fast wave. Although this yields the total power lost from the fast wave, it does not enable one to say how much power is damped locally because of cyclotron damping and how much propagates away in the Bernstein mode. In the present paper attention is turned to this problem and a coupling model is developed in which a Bernstein wave‐energy equation is derived and the power absorbed from the fast wave is used as a source for it. Information about the Bernstein wave amplitude is thus lost, but for both low‐ and high‐field incidence it is shown how the problem of fast‐wave and Bernstein wave‐energy propagation can be treated by a series of equations of no higher than second order that pose no numerical problems and can be integrated together as a single initial value problem. This yields a simple and efficient numerical technique, the results of which compare well with more complicated procedures.

ISSN:0899-8221    

DOI:10.1063/1.859147

出版商:AIP    

年代:1989

数据来源: AIP