摘要:

On the basis of the theory of&sgr;stability, a classification of high‐shear&sgr;‐stable diffuse pinch configurations is obtained by numerical solution of the Euler equation corresponding to the modified energy principle. Toroidal effects are introduced by putting a lower bound on the magnitude of the poloidal field in order to assure toroidal equilibrium and by deriving and employing the proper generalization of the Kruskal‐Shafranov limit form = 1unstable configurations. The classification of high‐shear&sgr;‐stable configurations consists of five different types, viz., tokamak,B&thgr;‐reversed pinch, screw pinch, combined pinch,Bz‐reversed pinch. Among the significant new results are: complete stability of some of the tokamak configurations for&bgr;up to 4&percent;, a stable high‐&bgr;(30&percent;)B&thgr;‐reversed pinch configuration that has not been investigated before, a stable diffuse screw pinch with&bgr; = 30&percent;when currents are allowed to flow at the wall and with&bgr; = 8&percent;with vanishing current at the wall, the possibility of containing diffuse high‐&bgr;m = 1stable plasmas withoutBz‐field reversal or pressure minimum on axis. Here,&sgr;stability refers to times needed for fusion.

ISSN:0031-9171    

DOI:10.1063/1.1694832

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The magnetohydrodynamic stability of a straight plasma column with elliptic cross section, carrying a uniform axial current, is investigated by extremizing the Lagrangian of the system using a natural coordinate system based on the magnetic field lines. Stability criteria are derived and growth rates are obtained analytically for systems with a uniform mass density inside the plasma. It is shown that the coupling between kink modes and Alfve´n waves produced by noncircularity is a destabilizing effect. A technique for solving the problem numerically is also discussed and used to demonstrate the effect of a spatially varying plasma density on the growth rate.

ISSN:0031-9171    

DOI:10.1063/1.1694833

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An analysis is made of one of the expected nonlinear and anomalous mechanisms and instabilities in the corona of a laser irradiated plasma. As is well known, nonlinear ponderomotive forces generate a net acceleration of the plasma toward lower densities. It is demonstrated that the same forces at oblique incidence of the radiation, can cause a net motion perpendicular to the well‐known forces along the density gradient: The standing wave generated that is split into zones (slabs) of the thickness of a quarter of a wave length, where the plasma is moving in the plane of incidence parallel and antiparallel to the slabs. This striated motion can also occur in an underdense plasma, while for the net acceleration toward lower density the strong change of the refractive index near the cutoff density is necessary. The striated parallel and antiparallel motion of the slabs is limited by the mean free path, by the velocity toward lower density and is determined by the condition of laminar and turbulent motion. The time constants on the order of picoseconds and the nonlinear absorption due to the generation of this striated motion are evaluated. Laser intensities exceeding 1013W/cm2incident at angles of 25° should build up striated jets with ion energies of a few keV.

ISSN:0031-9171    

DOI:10.1063/1.1694834

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The nonlinear mixing of two laser beams to drive a mode with a frequency near the cyclotron frequency of either the electrons or ions for plasma heating is investigated. The beat frequency wave that is generated is not required to be a natural mode in the plasma. As a result, the heating scheme is considerably less sensitive to fluctuations in the magnetic field, the plasma density, and in the frequencies of the mixing laser beams than in the case where a natural mode in the plasma is generated. The results that are obtained predict a considerable enhancement in the power absorption by the plasma in a region within the volume of interaction of the two laser beams. The extent of the strongly heated region is determined by the transfer of energy from the higher frequency laser to the lower frequency laser as the two beams propagate through the region of interaction.

ISSN:0031-9171    

DOI:10.1063/1.1694835

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A convergent Fokker‐Planck equation is derived for an electron plasma in a strong dc magnetic field. Conservation laws and anHtheorem are proved. The equation is manipulated into a form in which it is straightforward to evaluate magnetic‐field‐dependent relaxation times in terms of a series of modified Bessel functions.

ISSN:0031-9171    

DOI:10.1063/1.1694836

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Plasma rotation in the collisional regime is considered from the viewpoint of the driftkinetic equation, using orderings which have become standard in neoclassical transport theory. Kinetic arguments require a unique relation between the ion parallel flowUand the radial gradients of density, temperature, and electrostatic potential; this relation is derived and compared to similar relations for collisionless regimes. The off‐diagonal stress tensor component, which governs the time evolution ofUis also calculated. This component does not resemble a viscous stress, and dominates classical viscosity by roughly the usual Pfirsch‐Schlu¨ter factor.

ISSN:0031-9171    

DOI:10.1063/1.1694838

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The electric microfield distribution for weakly turbulent electron‐ion systems is calculated using an individual‐collective approach. The possibility of separation into collective ion, collective electron, and individual contributions due to electrons and ions is discussed. Analytical expressions for the collective electron and the collective ion microfield distribution are presented in terms of the turbulent spectrum. The results for the total distribution in the case of ion‐sound turbulence show significant deviations compared with those of plasmas in thermodynamic equilibrium.

ISSN:0031-9171    

DOI:10.1063/1.1694839

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The turbulent electron heating due to laser‐plasma instabilities at the critical density (laser frequency equals plasma frequency) is considered. In the regime where the laser energy is much less than the plasma thermal energy, simulations show that the wave energy spectrum takes on approximatek−2shape concomitant with the formation of a suprathermal electron tail. Test particle calculations demonstrate that these tails are produced by velocity space diffusion due to the plasma waves. Quasilinear theory predicts a linear heating rate and an exponential shape for the electron tail, in agreement with the simulation result. The fluid equations, including mode coupling terms, are solved, and it is found that the instability saturation level andk−2spectrum are due to mode coupling. Using the resulting fields, the electron distribution function is evolved, giving reasonable heating rates and suprathermal tail formation. Calculations in the underdense region (laser frequency greater than plasma frequency) show that the heated distribution function has fewer high energy electrons. Finally, an approximate analysis of heating in a finite interaction region is given.

ISSN:0031-9171    

DOI:10.1063/1.1694840

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

When a small test wave is launched near the frequency of a large amplitude electron plasma wave, the behavior of the test wave is determined by the nonlinear dynamics of the electrons that are trapped by the large amplitude wave. Consequently, the amplitude of the test wave oscillates coherently with the trapping oscillations in the amplitude of the main wave. The behavior of a small, launched, test wave at frequency&ohgr;is observed as a function of its frequency separation from a large amplitude electron plasma wave at frequency&ohgr;0.The initial damping and subsequent amplitude oscillations of the test wave are compared with a calculation in which the test wave is treated as a slow modulation of the amplitude and phase of the main wave. Test wave experiments agree with the calculation when&ohgr;0 − 4&pgr;/T < &ohgr; < &ohgr;0 + &pgr;/T,whereTis the transit time of the main wave through the experiment. When the spontaneously unstable frequency of the lower sideband is within this range, the slow amplitude oscillations of the sideband agree with the calculation. When the frequency of the test wave is sufficiently far below&ohgr;0 − 4&pgr;/T,the test wave damps according to linear theory. The phase velocity at which the test wave behaves essentially linearly determines the velocity of the fastest electrons that interact strongly with the wave.

ISSN:0031-9171    

DOI:10.1063/1.1694841

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Instabilities in a plasma containing electrons drifting relative to the ions and subjected to an intense ac electric field of frequency&ohgr;are investigated. The beat disturbance produced by the interaction of the driving field and ion density fluctuations of wavenumberkiaccelerates electrons of velocity&ohgr;/ki.If this is larger than the electron drift velocity, the acceleration enhances the current, while the recoil momentum imparted to the ion fluctuation can cause it to grow. The process has been simulated on a one‐dimensional plasma model and it was found that the small amplitude growth is in agreement with a theory which is a minor modification of that for the anomalous high‐frequency resistivity. Nonlinear effects ultimately saturate the growth of the instability and the current enhancement, and some discussion of these is given.

ISSN:0031-9171    

DOI:10.1063/1.1694842

出版商:AIP    

年代:1974

数据来源: AIP