摘要:

An attempt is made to go beyond the framework of conventional weak turbulence theory. A simple dispersion equation for the stability of a steady turbulent state can be found by selective summation of higher‐order terms from perturbation theory. The main contribution in the model to be considered here comes from particle motion in the turbulent electric field. In the limit of small wave amplitude, the usual equations of the weakly turbulent plasma can be obtained easily. The theory is applied to the drift‐cyclotron instability of a nonuniform plasma to find the steady‐state level of drift‐cyclotron turbulence. The growth rate of the instability changes essentially at the nonlinear stage, so the usual dimensional arguments to find the turbulent diffusion coefficient cannot be applied using the linear description only.

ISSN:0031-9171    

DOI:10.1063/1.1762219

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The turbulent plasma state which develops from unstable, current‐driven drift waves is analyzed. In the nonlinear theory, the wave growth predicted by the linear theory is ultimately suppressed by ion damping. Since the phase speeds of the unstable waves are much greater than the ion thermal velocity, the ions cannot absorb wave energy until they become trapped. The amplitude of the turbulent spectrum grows until trapping occurs, and a quasi‐steady state is reached in which the directed electron energy is converted into ion thermal energy at a constant rate. In this state the perturbation of the density gradient due to the turbulence is equal to the mean gradient. Nonlinear limitation due to mode coupling does not suppress the unstable wave growth until much larger density perturbations have developed. Therefore, ion trapping is established as the controlling nonlinear mechanism. In the steady state, the ions diffuse across the magnetic field with a diffusion coefficientD⊥≈ (k⊥−2&ggr;)max, where &ggr; is the growth rate predicted by the linear theory andk⊥is a perpendicular wavenumber. Although the detailed treatment is for a specific instability, the general conclusions appear to apply to a variety of drift waves.

ISSN:0031-9171    

DOI:10.1063/1.1762220

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Numerical analysis is made of the structure of one‐dimensional unsteady magnetic compression waves propagating into collisionless plasmas when the ambient magnetic field is oblique to the wave direction. Integration of the equations of motion is carried out by dividing the flow field into discrete elements or slabs of plasma and following their motion on a digital computer. Results from these calculations show that both the sub‐ and supercritical solutions change continuously from one limiting situation to the other. A similarity rule is found for correlating the subcritical cases so that the two‐parameter family of solutions in mass ratio and field angle are reduced to a single set.

ISSN:0031-9171    

DOI:10.1063/1.1762221

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

One‐dimensional flow of charged particles in a bounded system is investigated. In particular, the well‐known overlap of steady‐state solutions in the zero‐temperature flow approximation is examined in detail. A stability analysis is performed, and it is proved that not only the overlapping steady‐state solutions are unstable to infinitely small perturbations, but that all steady‐state flows in which partial reflection of charged particles from a virtual cathode is assumed, are also unstable.

ISSN:0031-9171    

DOI:10.1063/1.1762222

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Linearized equations are set up to describe the effect of an electrostatic wave on an anisotropic relativistic proton plasma embedded in a homogeneous magnetic field. It is assumed that a cold background plasma of protons and electrons co‐exists with the relativistic plasma. It is shown that instability arises whenever the relativistic proton plasma is anisotropic in the right sense. It is also shown that the growth rates are physically significant for galactic cosmic rays and thus space‐charge waves are a mechanism for producing some measure of isotropy in an anisotropic cosmic ray distribution. For instance, 10% anisotropy yields ane‐folding time of about 103years.

ISSN:0031-9171    

DOI:10.1063/1.1762223

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Electron velocity distribution functions for a partially ionized gas in a weak, steady electric field are obtained by solving the Boltzmann‐Fokker‐Planck equation numerically. As in the case of a fully ionized gas, the electron‐electron interactions in a partially ionized gas affect the velocity distribution function and, consequently, the electrical conductivity. Electrical conductivities are calculated for a variety of assumed electron‐molecule collision frequencies. The results differ by only a few percent from those obtained using an approximation suggested by Frost. A simple procedure, requiring no numerical integrations, is given relating electron temperature to electrical conductivity for a partially ionized gas.

ISSN:0031-9171    

DOI:10.1063/1.1762224

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

An effective momentum transfer collision frequency for electrons in cesium plasmas has been determined from measurements of the electrical conductivity and plasma properties in a cesium arc column. The effective collison frequency was found to depend on electron temperature in the 2500 to 4500°K range and to be significantly dependent on degree of ionization for values of this parameter greater than about 3 × 10−4, indicating a contribution from electron‐ion collisions. Numerical evaluations of the velocity integral for the electrical conductivity, modified to include electron‐ion as well as electron‐atom momentum transfer collisions, have been carried out using many trial functions for the electron‐cesium atom momentum transfer cross section. The electron‐atom cross section which has given the best fit between the calculated and measured conductivity exhibits a Ramsauer‐like minimum in the 0.25‐to 0.55‐eV range of electron energy.

ISSN:0031-9171    

DOI:10.1063/1.1762225

出版商:AIP    

年代:1967

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1762226

出版商:AIP    

年代:1967

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1762228

出版商:AIP    

年代:1967

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1762229

出版商:AIP    

年代:1967

数据来源: AIP