摘要:

The recombination instability described by D'Angelo is shown to constitute an example of a more general class of density change instabilities where over‐all density changes of gases and plasmas are caused by volumetric processes. A simplified version of the fluid mechanics equations pertaining to this problem is examined both in the linearized case and in the complete nonlinear complexity case.

ISSN:0031-9171    

DOI:10.1063/1.1692321

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The regions of instability of the ion flute mode are investigated for a low ‐&bgr;plasma in axisymmetric multipoles. A stability criterion is given including the effects of (1) finite Debye length, (2) small temperature anisotropy, and (3) small temperature gradient. Using quasilinear theory the growth of a spectrum of waves is shown to produce a stabilizing anisotropy. The level of density fluctuations in the saturated state is given for plasmas close to marginal stability.

ISSN:0031-9171    

DOI:10.1063/1.1692322

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

In thermally ionized alkali‐metal plasmas (Qmachines), two types of low‐frequency oscillations are found: the usual drift wave localized to the region of large‐density gradient, and a higher‐frequency wave localized to the region of the radial boundary. The latter “edge” oscillation is shown to be a Kelvin‐Helmholtz instability driven by the large shear in plasma rotational velocity at the boundary. An analytic solution of the finite‐Larmor‐radius dispersion equation for the unstable wave is found by making the simplifying assumption that the rotational velocity jumps discontinuously. The results agree reasonably well with experimental measurements.

ISSN:0031-9171    

DOI:10.1063/1.1692323

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The evolution of a collisionless beam plasma system initially in a linearly unstable state&egr;adjoining a marginally unstable state&egr;cris considered. This instability is a reactive effect, not a resonant particle effect. All phenomena are assumed to be periodic with a definite period along the beam direction. An examination is made to see whether a weak turbulence with an intensity depending on the deviation&Dgr;between&egr;and&egr;crand going to 0 with&Dgr;, or on the contrary a turbulence independent of&Dgr;develops in the plasma. To that end a study is made, using a variational method, to see whether a small‐amplitude ergodically periodic potential can exist in the plasma as a result of spontaneous evolution. It is found that this is impossible, and it is concluded that a turbulence with an intensity independent of&Dgr;develops in the plasma.

ISSN:0031-9171    

DOI:10.1063/1.1692324

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A static theory of density and potential distribution in a cylindrical beam‐generated plasma is presented. The theory requires only minor modifications of the Langmuir‐Tonks free‐fall theory for a positive column and is based on the assumption that the electron is the principal source of ionization. Both theoretical and experimental results for a singly ionized mercury plasma are given for the case of an electron beam partially filling a cylindrical tube.

ISSN:0031-9171    

DOI:10.1063/1.1692325

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Necessary and sufficient conditions for exponential stability of equilibria are obtained for the resistive, viscous, incompressible magnetohydrodynamic sheet pinch in a gravitational field. Insulating as well as conducting boundaries are considered. The unperturbed magnetic fieldB0(horizontal), resistivity&eegr;0, viscosity&ngr;0, and mass density&rgr;0are permitted to be arbitrary (neither necessarily constant nor small) functions of the vertical coordinatezconsistent with the equilibrium equations. In particular, it is shown that: (1) previous results claiming the existence of an exponentially growing “tearing” mode for a constant&eegr;0equilibrium with zero gravity are incorrect, (2) a nonconstant&eegr;0equilibrium with insulating boundaries cannot be gravitationally stabilized, and (3) a nonconstant&eegr;0equilibrium withg(d&rgr;0/dz) ≡ 0andB0nonunidirectional is exponentially unstable to all perturbations (i.e., waves of arbitrary wavelength) with certain directions of propagation.

ISSN:0031-9171    

DOI:10.1063/1.1692326

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A direct measurement is described of the perpendicular diffusion coefficient in a theta pinch operating in the low‐pressure regime with zero bias field. The diffusion was studied by comparing the measured time variation of the radial electron density distribution with computations assuming classical and other resistivities. A coil 8 m long is used in order to delay end effects and measurements confirm theoretical predictions that the plasma in the midplane is uninfluenced by the ends and free of energy losses for about 25&mgr;sec. The plasma temperature was varied from 90 to 160 eV and the values of density and beta on the axis are3−4 × 1016/cm3and 0.7, respectively. In the early stages (before 2&mgr;sec) diffusion at approximately the Bohm rate is found, and this is believed to be due to a streaming mechanism. At later times the measured diffusion coefficient is in good agreement with the classical value in all conditions studied, and the experimental error is such that diffusion is unlikely to exceed110of the Bohm rate.

ISSN:0031-9171    

DOI:10.1063/1.1692327

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The bremsstrahlung emitted from thermal plasmas which coexist with a flux of relativistic electrons is calculated. The emission is found to be greatly enhanced at the fundamental and second harmonic of the electron plasma frequency. Some possible astrophysical applications of the theory are discussed.

ISSN:0031-9171    

DOI:10.1063/1.1692328

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The energy spectrum and spatial distribution of neutrons emitted by a plasma focus device were measured with nuclear emulsions and scintillation detectors, and the results are reported. The average energy of the D‐D neutrons emitted along the axis was shifted∼500 keVcorresponding to an axial center‐of‐mass velocity of2 × 108 cm/secfor the reacting deuterons. An 11% anisotropy in the neutron fluxes measured in the forward and radial directions correlates with an axially streaming plasma which is not isotropic; the reacting deuterons collide predominantly in the radial direction. Time‐resolved collimation measurements of the emitted neutrons showed an axial translation of the neutron source corresponding to velocities up to2 × 108 cm/sec; this correlates with the nonsimultaneous pinching of the noncylindrical plasma along the axis. Plasma densities of∼ 2 × 1020cm−3and ion temperatures of 2 keV were consistent with observed neutron yields of1010and pulse widths of 60 nsec. X‐ray intensity measurements were made for x‐ray energies of7 < Ep < 30 keVand showed anEp−2dependence which does not agree with plasma bremsstrahlung, but appears to result from anode bombardment of axially accelerated electrons with energies> 200 keV. The line radiation corresponded to that of fairly cold ions.

ISSN:0031-9171    

DOI:10.1063/1.1692329

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The motion of charged particles in combined betatron and azimuthal magnetic fields is investigated for the case when the radial betatron focusing force vanishes.

ISSN:0031-9171    

DOI:10.1063/1.1692330

出版商:AIP    

年代:1969

数据来源: AIP