摘要:

From the nonlinear gyrokinetic equation we formulate the renormalized turbulence equation for the &eegr;i‐mode drift wave instability. The study shows that the dominant nonlinear damping mechanism is from theE×Bconvection of the pressure fluctuation and that the kinetic modifications to the fluidE×Bmode coupling, studied earlier, shift the spectrum toward the shorter wavelengths. Balancing the linear growth rate with the nonlinear damping rate at the linearly most unstable region, we calculate the anomalous ion thermal conductivity, which exceeds the neoclassical plateau formula and gives a value of the same order as that previously computed by Horton, Choi, and Tang [Phys. Fluids26, 1077 (1981)], but with a kinetic enhancement factor. Also, the thermal conductivity formula remains finite for vanishing density gradient.

ISSN:0031-9171    

DOI:10.1063/1.865616

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The Lighthill–Giles [Philos. Trans. R. Soc. London Ser. A252, 397 (1960); J. Plasma Phys.19, 201 (1978)] method is extended to evaluate the far field resulting from a moving radiating source in an anisotropic and dispersive medium, and the result thus obtained has a retardation interpretation. The radiation energy flux derived from theJ⋅Emethod, only after a modification resulting from anisotropy of the medium and a correction factor resulting from retardation, is found to be compatible with that directly calculated from the far field, provided interference may be neglected. While the interference, which arises from the mixed product of any two far‐field terms of different wave vectors, is demonstrated to be completely null in a uniaxial medium for a stationary source, it is shown to exist in a gyrotropic magnetoplasma and the total Poynting vector could be substantially nonradial in certain special cases.

ISSN:0031-9171    

DOI:10.1063/1.865617

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Semicollisional drift‐tearing modes are studied analytically in toroidal plasmas. Corresponding differential equations for the eigenmodes are derived via the ballooning mode representation and flux‐surface averaging. A dispersion relation is then obtained using asymptotic matching. It is found that the stabilizing effects of good average curvature and finite plasma compression lead to a tearing instability threshold &Dgr;c, which is independent of the resistivity.

ISSN:0031-9171    

DOI:10.1063/1.865618

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Runaway effects on lower‐hybrid current ramp‐up are studied numerically using a two‐dimensional Fokker–Planck analysis and a nonlinear circuit equation. Runaway contribution to the inductance is shown to be important in limiting the magnitude of the induced electric field. This tends to reduce the current ramp‐up efficiency. However, for a range of &ohgr;p/&OHgr;, the anomalous Doppler instability can be excited and the runaway production rate as well as the associated inductance is significantly reduced when that happens. This allows the ramp‐up efficiency to be further increased.

ISSN:0031-9171    

DOI:10.1063/1.866007

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Nonlinear, nondissipative ponderomotive theory is developed in relation to recent experimental results showing that externally imposed rf fields can stabilize an axisymmetric mirror plasma. First, the ponderomotive force problem is reexamined, with emphasis on self‐consistency of the interaction between the plasma and high‐frequency field. The averaged action principle for the antenna–plasma system yields self‐consistent plasma and electromagnetic field dynamics on the oscillation‐center time scale. The plasma equilibrium condition is expressed as a balance among plasma and magnetic pressure forces, including interchange, ponderomotive, and magnetization forces. Next, the spectral stability of such static equilibria is studied in the low‐frequency magnetohydrodynamic (MHD) approximation, with a &Dgr;Wprinciple that incorporates the various ponderomotive contributions: particle effects, magnetization effects, and self‐consistent adjustment of the rf field resulting from displacements of the plasma away from equilibrium. The ponderomotive potential energy functional is related to the antenna inductance and antenna current amplitude. Finally, the noncanonical Hamiltonian formulation for the system’s dynamics is given, in terms of Eulerian fields. It allows the construction of nonlinearly conserved functionals, which yield criteria for linearized Lyapunov stability, for both multifluid and MHD models. The Lyapunov stability conditions are related to the modified &Dgr;Wvariational principle.

ISSN:0031-9171    

DOI:10.1063/1.865619

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The low‐frequency stability of a compact‐torus ion‐ring hybrid configuration, in which part of the toroidal current is carried by a ring of high‐energy ions, is studied. In particular, the magnetohydrodynamic (MHD) tilt and radial shift instabilities in spheromak‐like hybrid systems are considered. The ion ring has a stabilizing effect on the tilt mode, through its modification of the magnetic geometry. For the shift mode, the stabilization is dynamic for moderate elongation, but is again geometrical in the limit of large elongation. For moderate elongation, it is found that a high‐energy ion component substantially enhances stability against the MHD shift mode.

ISSN:0031-9171    

DOI:10.1063/1.865620

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Nonlinear evolution of three‐dimensional magnetohydrodynamic (MHD) instabilities of a toroidal spheromak in a cylindrical flux conserver has been studied by numerical simulations for various initial equilibrium states with differentqprofiles. In spheromaks withqa>1, whereqais the safety factor on the magnetic axis, nonlinear evolution of the resonant internal kink mode dominates with a poloidal mode numberm=1 and a toroidal mode numbern=1 that causes the poloidal flux amplification. This process corresponds to that of the internal disruption model for tokamaks by Kadomtsev [Sov. J. Plasma Phys.1, 389 (1975)]. In spheromaks with a very highqa, namelyqa≳3, the grossn=1 kink mode grows extensively in the region including the major axis of the torus, which causes the flux conversion from the toroidal to poloidal directions. For spheromaks with a lowqa, namelyqa≲0.5, the internal kink mode with a toroidal mode numbern∼1/qais first destabilized, and the excitation of the modes with lowernnumbers down ton=1 proceeds, while then=2 mode saturates. Nonlinear coupling of various modes leads to the flux conversion from the poloidal to toroidal directions. When a center conductor is present in this case, a reversed‐field pinch (RFP) configuration once formed is sustained. Relaxations through pressure‐driven modes are also discussed. All final states obtained in our simulations are quite near the Taylor state with an excess magnetic energy less than 10% of that of the Taylor state.

ISSN:0031-9171    

DOI:10.1063/1.865621

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An approximate analytic solution of the magnetohydrodynamic (MHD) equilibrium equation for large‐aspect‐ratio, helically symmetric systems is obtained. The resistive ballooning stability of these equilibria is studied numerically and analytically. We find that the ballooning modes scale as the resistivity to the third power. They are driven by the helical nature of the magnetic axis and by the elliptic distortion of the flux surfaces away from a circle.

ISSN:0031-9171    

DOI:10.1063/1.865622

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Using multiple time scale analysis, the nonlinear saturation of the absolute stimulated Raman scattering instability is examined in a finite homogeneous collisional plasma. The amplitude of the incident wave is assumed to exceed the absolute instability threshold by the fractional amount &Dgr;(≪1). A single backscattered wave and a single plasma wave grow until time‐asymptotic saturation occurs. The reflected light intensity is determined analytically and is proportional to &Dgr;. The spatial variation of the saturated wave amplitudes is also obtained. The reflected intensity is compared to the values predicted for the convective instability, for incident intensities which are marginally less than the absolute threshold intensity. In ‘‘short’’ plasmas, i.e., ones which extend over only a few linear convective gain lengths, the reflected light intensity is found to be much higher when the absolute instability is excited.

ISSN:0031-9171    

DOI:10.1063/1.865623

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The implosion dynamics of a hollow cylindrical neon gas‐puff plasma are investigated using a 1‐D non‐localthermodynamicequilibriumradiation hydrodynamic model. Two cases are considered: the implosion of the gas puff with and without a low‐density central core plasma. It is shown that the implosion efficiently converts the kinetic energy of runin into radiation and that the radiation plays a significant role in the implosion energetics. For each case, the history of the implosion dynamics and emission spectra are presented as well as the distribution of radiative energy in the L and K shells. Finally, a comparison is made with purely hydrodynamic calculations.

ISSN:0031-9171    

DOI:10.1063/1.865624

出版商:AIP    

年代:1986

数据来源: AIP