摘要:

An experimentally determined diffusion coefficient is related to the amplitude of a continuum spectrum of drift‐wave‐like fluctuations. It is found that the diffusion coefficient depends upon the amplitude of the fluctuation in a way which is consistent with the nonlinear diffusion theory of Dupree; that is,D⊥ ∼ ⟨&dgr;n2⟩for small amplitude and∼ ⟨&dgr;n2⟩1/2for large amplitude. An elementary model which predicts the relative fluctuation amplitude⟨&dgr;n2⟩/n02and the autocorrelation time of the continuum spectrum of driftlike waves is also presented and shown to be in agreement with both the properties of the observed spectrum and the results of the diffusion measurements.

ISSN:0031-9171    

DOI:10.1063/1.1692356

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The boundary layer between a cold streaming plasma and a perpendicular magnetic field is treated for the case where significant charge separation effects occur and the electrons but not the ions are relativistic. This case is characterized by1 ≲ &ggr; ≪ M/2m, where&ggr; = Mu2/2mc2is the ratio of the initial ion streaming energy to the electron rest energy. Only the over‐all charge neutral boundary layer in which the electrons turn in the magnetic field before the ions is considered. It is found that the length scale of the magnetic field before the electron turning point is the plasma skin depthc/&ohgr;peas in the boundary layer with&ggr; ≪ 1, but that the electron number density diverges near the turning point with a length scale at leastu/csmaller. For large&ggr;the fraction of the ion streaming energy gained by the electrons as kinetic energy is approximately(2/&ggr;2)1/2, and the ions are found to penetrate a distance somewhat less than(2/3)(u/&ohgr;pi)beyond the electrons.

ISSN:0031-9171    

DOI:10.1063/1.1692357

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The following macroscopic equation is shown to govern the time development of a nonlinear ion acoustic wave:∂n∂&tgr; + &agr;2n ∂n∂&xgr; + &agr;3 ∂3n∂&xgr;3 + &agr;1(8&pgr;)1/2 P −∞+∞ ∂n∂&xgr;′ d&xgr;′&xgr; − &xgr;′ = 0, wheren,&xgr;, and&tgr;are normalized wave amplitude, space, and time coordinates, and&agr;1,&agr;2,&agr;3are parameters which depend on the relative strengths of Landau damping, nonlinearity, and dispersion. The first three terms constitute the Korteweg‐deVries equation, and the last term represents the effect of Landau damping. The equation conserves the number of particles but the wave energy can be shown to decay always. It is demonstrated that an initial waveform may either steepen or not depending on the relative size of the nonlinearity as compared to Landau damping. It is also shown that the Landau damping term causes the amplitude of a solitary wave to decay with time as(&tgr;+&tgr;0)−2.

ISSN:0031-9171    

DOI:10.1063/1.1692358

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

It is shown that a cold plasma in a weak magnetic field coexisting with a low density of energetic electrons is linearly and nonlinearly unstable if the distribution of energetic electrons is of the loss cone type, or is spherically symmetric in velocity space but nearly monoenergetic. Growth rates for linear and nonlinear instabilities are calculated and compared. It is shown that nonlinear growth rates may dominate for very low wave energy.

ISSN:0031-9171    

DOI:10.1063/1.1692359

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

It is shown that the wave properties of a magnetized plasma column, i.e., of a bounded magnetized plasma, at low incident high‐frequency power determine the behavior of the column at high hf power. At high hf power, the energy absorbed is sufficient to sustain the plasma in one of its linear (i.e., low‐power) resonant states. The plasma can either be sustained in one of its cold plasma resonant states or in its hot plasma resonant states. A partially quantitative theoretical picture can be drawn and maxima of the density as a function ofB0(static magnetic induction) exactly predicted. In this manner densities high above critical density (&ohgr;e > &ohgr;;&ohgr;is the angular frequency of hf field;&ohgr;eis the electron plasma frequency) can be obtained in the neighborhood of the lower cyclotron harmonics and along the upper branch of the cold plasma resonances. Ejection of plasma outside the interaction region between plasma and wave is observed. This ejection gives rise to plasma “tongues” with density maxima not correlated to the density of plasma in the interaction region. Low‐frequency instabilities and the generation of harmonics are also investigated.

ISSN:0031-9171    

DOI:10.1063/1.1692360

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

One‐dimensional numerical simulation of plasmas consisting of two unequal warm beams has shown flattening of the small beam and, in most cases, a strong single mode structure at about the wavelength of largest linear growth rate, accompanied by an eddylike arrangement of trapped particles in phase space. The total electrostatic field energy first increases at the linear growth rate and then, after saturating abruptly, decreases at about the same rate to an intermediate level where a much slower decay begins.

ISSN:0031-9171    

DOI:10.1063/1.1692361

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

It is shown that in a cylindrical waveguide, a long‐wavelength electron plasma wave steepens exactly as does a nonlinear sound wave. Possible applications to experiments are discussed.

ISSN:0031-9171    

DOI:10.1063/1.1692362

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The injection of a plasma stream into a transverse magnetic field by polarization andE × Bdrift is considered in terms of a simple model. An estimate of the peak flux density that the plasma can enter is discussed. An expression for the magnitude of the diamagnetism associated with the particle velocity distribution is indicated. Experiments on the motion of a plasma stream through regions of shorted (or tied) field lines show that a sheath forms on the shorting electrode and that the plasma can penetrate through the shorted lines because the discharge current is limited to the ion saturation current. An expression for the stopping distance is derived.

ISSN:0031-9171    

DOI:10.1063/1.1692363

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Insertion of current‐carrying loops, perpendicular to the field and inside the plasma region, can localize the ballooning mode in a stellarator. Estimates of the efficiency of such rings indicate that present instability concepts can be tested on existing stellarators.

ISSN:0031-9171    

DOI:10.1063/1.1692364

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Steady slow elongational flow of a dilute suspension of viscoelastic spheres is analyzed within the framework of the theory of oriented fluids.

ISSN:0031-9171    

DOI:10.1063/1.1692365

出版商:AIP    

年代:1969

数据来源: AIP