摘要:

The effects of density, temperature, and velocity gradients on four‐wave mixing (FWM) in a plasma are investigated. A fluid model is used in which the stimulated Brillouin terms are included, but pump depletion is neglected. The steady state phase conjugate reflectivity and signal transmission coefficients are calculated and discussed for both degenerate and resonant FWM. The substantial effects of inhomogeneity on the use of FWM as a plasma diagnostic are discussed.

ISSN:0899-8221    

DOI:10.1063/1.858934

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The extension of gyrokinetic theory to arbitrary frequencies by Chen and Tsai [Phys. Fluids26, 141 (1983); Plasma Phys.25, 349 (1983)] is used to study cyclotron absorption in a straight magnetic field with a perpendicular, linear gradient in strength. The analysis includes the effects of magnetic field variation across the Larmor orbit and is restricted to propagation perpendicular to the field. It yields the following results for propagation into the field gradient. The standard optical depths for the fundamental O‐mode and second harmonic X‐mode resonances are obtained from the absorption profiles given in this paper, without invoking relativistic mass variation [see also Antonsen and Manheimer, Phys. Fluids21, 2295 (1978)]. The compressional Alfve´n wave is shown to undergo perpendicular cyclotron damping at the fundamental minority resonance in a two‐ion species plasma and at second harmonic resonance in a single‐ion species plasma. Ion Bernstein waves propagating into the second harmonic resonance are no longer unattenuated, but are increasingly damped as they approach the resonance. It is shown how the kinetic power flow affects absorption profiles, yielding information previously obtainable only from full‐wave theory. In all cases, the perpendicular cyclotron damping arises from the inclusion of magnetic field variation across the Larmor orbit.

ISSN:0899-8221    

DOI:10.1063/1.858935

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The integrodifferential equation describing the linear tearing instability in the bi‐Maxwellian neutral sheet is solved without approximating the particle orbits or the eigenfunction &psgr;. Results of this calculation are presented. Comparison between the exact solution and the three‐region approximation [Phys. Fluids27, 1198 (1984)] motivates the piecewise‐straight‐line approximation, a simplification that allows faster solution of the integrodifferential equation, yet retains the important features of the exact solution.

ISSN:0899-8221    

DOI:10.1063/1.858936

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The coupled drift‐shear Alfve´n mode including the complete Bessel function gyroradius effect and the ∇⊥B‐curvature guiding center drift resonance of kinetic theory is solved for the toroidal ballooning mode eigenvalues and eigenfunctions. Comparisons between nonlocal (ballooning) and local kinetic theory and between nonlocal fluid and kinetic theory are made. The critical plasma pressure for kinetic ballooning mode instability is only the same as the magnetohydrodynamic (MHD) theory critical pressure &bgr;MHDfor &eegr;i=0. The critical kinetic theory plasma pressure &bgr;K(&eegr;i) is well below &bgr;MHDand the kinetic theory growth rate is unstable for allk. The MHD second stability region is also unstable in the kinetic theory. The kinetic theory growth rate is a maximum aroundk≤0.3–0.5 for finite aspect ratio &egr;n=rn/R. The effects of trapped electrons are found to be weakly stabilizing both analytically and numerically, and the instability is still significant outside the ideal MHD stable window from the ion magnetic drift resonances when &eegr;i≳1. The kinetic growth rate is a function of the six dimensionless parametersk,q2&bgr;, &egr;n,s, &eegr;i, and &tgr;=Te/Ti.

ISSN:0899-8221    

DOI:10.1063/1.858937

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A recently developed congruent reduction technique is applied to the parametric amplification problem in space‐ and time‐varying plasmas. The systematic reduction procedure yields a second‐order system of partial differential equations describing mode coupling in the presence of a strong pump wave. This system is similar in form to that characterizing the general multidimensional mode conversion problem so that the solution in both cases proceeds similarly. The method allows a consistent derivation of the expression for the parametric amplification coefficient in general geometry. An unmagnetized plasma case is considered as an example.

ISSN:0899-8221    

DOI:10.1063/1.858938

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Based on the formalism developed in another paper [Phys. Fluids 31, 3362 (1988)], three analytical results are obtained relating to (1) a WKB type of equation in inhomogeneous plasma, (2) the Raman process at (1/4)nc, and (3) two plasma decay processes at (1/4)nc. Interesting scaling results are found.

ISSN:0899-8221    

DOI:10.1063/1.858939

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Low‐level electrostatic ion acoustic turbulence generated by the ion–ion beam instability was investigated numerically. It is demonstrated that a conditional statistical analysis can reveal the formation, propagation, and decay of negative potential wells which correspond to ion phase‐space vortices. While the statistical analysis gives results in terms of averages over a conditionally selected subensemble,individualphase‐space structures can be investigated by small clusters of test particles placed at selected positions in phase space. The predictions of the conditional statistical analysis can be tested and their accuracy estimated by this method. A discussion of various aspects of test particle dynamics in turbulent plasmas follows naturally, with particular emphasis on conditioned particle release and relative diffusion of particles. The statistical properties of the fluctuating electric fields sampled along Lagrangian particle orbits is analyzed.

ISSN:0899-8221    

DOI:10.1063/1.858940

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

External magnetohydrodynamic modes stabilized by the presence of a close‐fitting perfectly conducting wall become destabilized when the wall is assumed to possess finite resistivity. A simple variational principle giving an estimate for the resulting growth rate and the threshold for stability is derived in terms of quantities relating to the ideal system with and without a perfectly conducting wall. This variational principle is valid for an arbitrary three‐dimensional external mode in an arbitrarily shaped plasma possessing an arbitrarily shaped, but thin, resistive wall. As an example of the utility of the method, the variational principle is used to investigate the axisymmetric (n=0) stability of straight, zero pressure elliptical tokamaks with arbitrary current density profiles in the presence of a resistive wall.

ISSN:0899-8221    

DOI:10.1063/1.858941

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Ionization and edge‐density gradient effects on the long‐wavelength radiative condensation (MARFE) instability in tokamak edge plasmas are considered. A self‐consistent coupled equilibrium is derived from the continuity and temperature equations including the effects of radiation and ionization. In the limit relevant to edge plasmas, a modification of the temperature equilibrium derived earlier [Phys. Fluids30, 2429 (1987)] is obtained due to the rapid edge‐density variations. The critical radiation (density) limit is enhanced and results in significantly larger growth rates for the pure radiative mode than previously reported. Ionization processes affect the MARFE through a source term in the continuity equation, and produce an effect which qualitatively depends on the edge temperatureTL. ForTLless than a critical temperature, ionization phenomena weaken the MARFE instability. This behavior reverses at higher temperatures.

ISSN:0899-8221    

DOI:10.1063/1.858942

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The effect of finite parallel wavenumber and electron temperature gradients on the lower hybrid drift instability is studied in the parameter regime corresponding to the TRX‐2 device [Fusion Technol.9, 48 (1986)]. Perturbations in the electrostatic potential and all three components of the vector potential are considered and finite beta electron orbit modifications are included. The electron temperature gradient decreases the growth rate of the instability but, forkz=0, unstable modes exist for &eegr;e(=T’en0/Ten0)>6. Since finitekzeffects completely stabilize the mode at small values ofkz/ky(&bartil;5×10−3), magnetic shear could be responsible for stabilizing the lower hybrid drift instability in field‐reversed configurations.

ISSN:0899-8221    

DOI:10.1063/1.858943

出版商:AIP    

年代:1989

数据来源: AIP