摘要:

The linear Vlasov theory of the universal instability driven by a density gradient in a unidirectional magnetic field is considered in the slab model with the local approximation. The electrostatic approximation is used, but the full resonant effects of a magnetic field gradient drift are included for the ions. Both electron and ion ∇Beffects reduce the growth rate, but the latter is more important. It is shown that the nonresonant ion ∇Bapproximation fails at relatively low &bgr; and that the conventional resonant ion approximation becomes invalid as &bgr; increases.

ISSN:0031-9171    

DOI:10.1063/1.862638

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The full electron dynamics in the collisionless drift wave radial equation is used to discover a class of drift modes which are localized by electron temperature gradients and are unaffected by the ion acoustic term. In the presence of a driving term, such as provided by trapped particles, these modes become strongly unstable.

ISSN:0031-9171    

DOI:10.1063/1.862639

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Resistivem=1 modes associated with minidisruptions of current carrying plasmas are shown to be strongly influenced simultaneously by the effects of finite ion gyroradius, finite drift wave frequency, and ion‐ion collisions in the plasma regimes of interest. The modes acquire finite frequency of oscillation and, for low &bgr;, the reduction in their growth rates is due mainly to the drift wave frequency, the effect of ion‐ion collisions being slight (less than 10% effect); but, even for low &bgr;, ion‐ion collisions significantly alter the radial structure of the modes. As a result, the reconnecting mode, which tends to lose its radial localization above a threshold temperature, remains well‐localized when ion‐ion collisions are included.

ISSN:0031-9171    

DOI:10.1063/1.862640

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Nonlinear electron plasma oscillations driven by an electromagnetic wave are investigated. An improved, self‐consistent Lagrangian description of the resonant interaction is derived. The modifications to the simple capacitor plate or uniform electrostatic driver model previously employed are calculated and shown to have a negligible effect on the wavebreaking process for laser intensitiesI<1017W cm−2in the case of Nd lasers.

ISSN:0031-9171    

DOI:10.1063/1.862648

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An infinitely long, thin, field‐reversing ion layer immersed in a much denser, cooler background plasma is examined for instabilities driven by the velocity difference between the layer ions and the background plasma, taking into account the radial mode structure, as well as Landau damping by the background plasma. The only instability is the low frequency (&ohgr;≪&OHgr;i) magnetosonic mode; the worst mode has growth rate &ggr;∼&ohgr;∼vA/a, andk‐‐∼k⊥∼a−1, whereais the width of the layer. This mode might be stabilized by electron Landau damping and transit‐time magnetic damping, when the temperature of the layer ions is comparable to their energy.

ISSN:0031-9171    

DOI:10.1063/1.862649

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The theory of astron ion‐ring equilibria is considered from a new point of view. In contrast with previous equilibria, the new equilibria have a distribution of canonical momentum which is invariant to axisymmetric changes in the external magnetic field. As a function of the single particle constants of the motion, the energyH, and the canonical momentumP&Vthgr;, the distribution function,f(H,P&Vthgr;) is written asf=g(P&Vthgr;)F(H,P&Vthgr;)[A(H,P&Vthgr;)]−1. Here,g(P&Vthgr;) is the invariant distribution function for canonical momentum;A(H,P&Vthgr;) is the area of the poloidal (r,z) plane accessible to a ring particle with constantsHandP&Vthgr;; andF(H,P&Vthgr;) is a nonnegative function having the normalizationF dH F=const. The possibility of a third constant of the single particle motion is not included. In contrast with some previous equilibria,f(H,P&Vthgr;) is nonzero only in the regions of theP&Vthgr;,Hplane in which there are trapped particle orbits. With this representation off, it becomes possible to study the adiabatic compression of ion‐ring Vlasov equilibria.

ISSN:0031-9171    

DOI:10.1063/1.862650

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A study is made of the stability of the low‐frequency precession and kink modes of a long astron particle layer embedded in a dense low‐temperature plasma. The precessional motion corresponds to a toroidal mode numbern= 1 and the kink motion ton≳ 2. Two types of precession of nonrelativistic ion layers are analyzed in detail. For frequencies &ohgr; such that &agr;2&OHgr;2≪‖&ohgr;‖2≪&OHgr;2, there is a precession mode with the real part of the frequency &ohgr;r≈−(&eegr;e/2) &OHgr;. Here, &OHgr; is the average circulation frequency for the layer ions; &agr;≡ vA/v¯&Vthgr;≪ 1 withvAthe plasma Alfve´n wave speed, and v¯&Vthgr;the average azimuthal velocity of the layer ions; and &eegr;eis the effective external magnetic field index. This mode shows the well known negative energy type of instability due to dissipation for &eegr;e< 0, which corresponds to a mirror field. For frequencies ‖&ohgr;‖2≪&agr;2&OHgr;2, there is a magnetohydrodynamic precession mode with a frequency &ohgr;≈± (&eegr;e/&zgr;)1/2&agr;&OHgr;, where &zgr; is the loading factor, which is a measure of the layer strength. This mode has a magnetohydrodynamic type of instability for &eegr;e< 0. For the kink modes, a necessary and sufficient condition for stability is shown to be &eegr;s< 3, where &eegr;sis the self‐magnetic field index.

ISSN:0031-9171    

DOI:10.1063/1.862651

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The electrostatic stability properties of a rotating, charge‐neutralizedP‐layer are investigated within the framework of a hybrid (Vlasov‐fluid) model in which the layer ions are described by the Vlasov equation, and the layer electrons and the uniform background plasma are described as macroscopic, cold fluids. It is assumed that thePlayer is thin, with radial thickness (2a) much smaller than the mean radius (R0), and that &ngr;≪1, where &ngr; is Budker’s parameter for the layer ions. Electrostatic stability properties are calculated for perturbations about a weakly diamagneticPlayer with rectangular density profile, described by the equilibrium distribution functionf0b= (nbR0/2&pgr;mi) &dgr;[H−VzPz−mi(V20−V2z)/2]&dgr; (P&Vthgr;−P0), whereHis the energy,P&Vthgr;is the canonical angular momentum,Pzis the axial canonical momentum, andnb,R0,Vz,V0, andP0are constants. The stability analysis is carried out including the effects of a uniform background plasma, and weak self‐magnetic fields. Although a slow rotationalPlayer (P0≳0) is found to be stable, it is shown that a fast rotationalP‐layer (P0<0) is unstable for sufficiently high background plasma density (&ohgr;2p≫&ohgr;2ci). The typical instability growth rate is a substantial fraction of the ion cyclotron frequency.

ISSN:0031-9171    

DOI:10.1063/1.862652

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The equations of magnetohydrodynamic equilibrium are solved using the rigid‐drift assumption for a screw pinch with an arbitrarily pitched current. Instead of the customary isothermal assumption, the pressure is assumed to be proportional to the square of the number density (which implies a temperature that is proportional to the number density). Analytical formulae are presented for the profiles of the equilibrium magnetic field components,B&Vthgr;(r) andBz(r), and for the equilibrium pressure profile,p(r). The relative shapes of these profiles (which can exhibit hollow pressure and/or reversedBzbehavior) are determined by specification of only two parameters: the value of the local plasma beta atr=0 and a quantity related to the pitch of the current. A set of profiles that resemble those experimentally observed in reversed‐field pinches is presented.

ISSN:0031-9171    

DOI:10.1063/1.862653

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A reduced set of two‐fluid transport equations is obtained from the conservation equations describing the time evolution of the differential particle number, entropy, and magnetic fluxes in an axisymmetric toroidal plasma with nested magnetic surfaces. Expanding in the small ratio of perpendicular to parallel mobilities and thermal conductivities yields as solubility constraints one‐dimensional equations for the surface‐averaged thermodynamic variables and magnetic fluxes. Since Ohm’s law E +u×B =R′, where R′ accounts for any nonideal effects, only determines the particle flow relative to the diffusing magnetic surfaces, it is necessary to solve a single two‐dimensional generalized differential equation, (∂/∂t) ∇&psgr;. (∇p− J×B) =0, to find the absolute velocity of a magnetic surface enclosing a fixed toroidal flux. This equation is linear but nonstandard in that it involves flux surface averages of the unknown velocity. Specification of R′ and the cross‐field ion and electron heat fluxes provides a closed system of equations. A time‐dependent coordinate transformation is used to describe the diffusion of plasma quantities through magnetic surfaces of changing shape.

ISSN:0031-9171    

DOI:10.1063/1.862654

出版商:AIP    

年代:1979

数据来源: AIP