摘要:

It is found that the helicity of a photon in a plasma is conserved in the process of the parametric scattering instability along the magnetic field. This fact may be utilized to help diagnose the scattering instabilities by an intense laser in a plasma. The growth rates of these instabilities are given as modifications to those without a static magnetic field.

ISSN:0031-9171    

DOI:10.1063/1.861707

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A newly developed numerical model is described which calculates plasma implosion on the Alfve´n wave time scale, appropriate for modeling cylindrical pinch experiments. The simulation includes fluid electrons, particle ions, cylindrical geometry, and self‐consistent plasma turbulence effects on the resistivity and the ion and electron heating. A series of trial runs is presented to document the effect of including or neglecting turbulent ion heating and cylindrical geometry in the model.

ISSN:0031-9171    

DOI:10.1063/1.861708

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The stability of a periodic magnetic island structure using the ideal magnetohydrodynamic equations has been investigated. An instability is found which describes the tendency toward coalescence of parallel currents in the neighboring islands. It is expected that this instability will proceed at a fast hydromagnetic rate as long as the forces driving the instability can overcome the stabilizing forces due to the compression of the magnetic field between the islands. Beyond that phase, resistivity is expected to dominate the tendency toward island coalescence. Island coalescence of this kind can explain why in the observation of tearing mode instabilities in tokamaks, only the modes with minimum values ofmandnare seen.

ISSN:0031-9171    

DOI:10.1063/1.861709

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A previous calculation of the single‐mode nonlinear saturation of the bump‐on‐tail instability assumed immobile ions. Here, the ions are also allowed to respond. The usual van Kampen continuum of real eigenmodes is shown to change to a double continuum. The analog of the Case class 1cmode is now singular and has an undetermined coefficient. The corresponding charge density is however nonsingular. The nonlinear calculation carries through as before, and the result is an obvious generalization of the one‐component case. Total energy and momentum are conserved, but the partition of momentum and energy between ions and electrons is not determined by asymptotic considerations alone. The result also applies to the threshold region for the ion‐sound instability.

ISSN:0031-9171    

DOI:10.1063/1.861710

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The effect of the helical instability on the internal magnetic field in the positive column, is investigated theoretically under the assumptions that the densities of electrons and ions are perturbed independently and that the perturbed densities have finite amplitudes. The internal magnetic field is found as a function of the amplitude of the superimposed helix for the helical instability (m=1) and the phase shift &dgr;mbetween the perturbed densities of electrons and ions. The theoretical results are compared with experimental data and found to be in fair agreement with experimental values. It is concluded that the direction of the internal magnetic field produced by the helical instability is parallel to that of the applied magnetic field.

ISSN:0031-9171    

DOI:10.1063/1.861711

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A low‐frequency flute instability in a collisionless plasma flowing along a curved magnetic field has been observed to localize in regions of bad curvature (∇B2∇≳0). The experiment was performed in a single‐endedQmachine. A low density plasma was injected along the lines of force which were bent into the arc of a circle. As the flow velocity of the plasma was increased, the flute type oscillations were found to be stabilized in the region of good curvature and to be destabilized in the region of bad curvature. The experimental results are well explained by simplified calculations. For slow flow velocity the instability is mainly driven by a transverse Kelvin–Helmholtz effect due to the velocity shear of the E×B rotation, so that it is almost independent of the magnetic field curvature. For large velocities, however, the curvature effect stems from a Rayleigh–Taylor ’’gravitational’’ effect due to the centrifugal force, which makes the oscillation localize in the region of bad curvature.

ISSN:0031-9171    

DOI:10.1063/1.861712

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

An analysis is presented of an experimental study of the scattering of microwaves by density fluctuations due to the current‐driven ion acoustic wave instability in a toroidal plasma confinement device, the FM‐1 spherator. It is found that the instability exists only in the collisional regime (where &ngr;ef≳&ohgr;be) and it is inhibited (i.e., quenched by two orders of magnitude) in the trapped‐electron banana regime (where &ngr;ef<&ohgr;be). Further, it is found that for two different values of the ratio of the trapped to untrapped electron number density (i.e., for both 70% and 40% mirror trapping) this inhibition always starts to occur when &ngr;ef≈&ohgr;be. Finally, it is shown that the nature of this inhibition is in general agreement with the recent theoretical notion that in the banana regime the entire Ohmic heating current is carried only by the freely circulating electrons.

ISSN:0031-9171    

DOI:10.1063/1.861713

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A simple yet novel rf exciter structure has been developed for generating remotely intense rf fields in a magnetoplasma. It is a circular line source of radiusRin a plane ⊥B0driven with an rf signal at &ohgr; <&ohgr;c≃&ohgr;p(where &ohgr;c, &ohgr;pare the electron cyclotron and electron plasma frequency, respectively) which excites two resonance cones with focal points atz=±Rcot&THgr;c(&THgr;cis the cone angle). The rf intensity increasesawayfrom the exciter to reach a maximum (approximately 20 dB enhancement) at the remote focal points. This arrangement is ideally suited to study nonlinear interactions free of boundary effects. At large applied rf signals, &egr;0Erf2/nkTe≳0.2, a strong density depression in the focal region (&dgr;n/n≳40%) is observed. The density perturbation modifies the cone angle and field distribution. This nonlinear interaction leads to a rapid growth of ion acoustic wave turbulence and a corresponding random rf field distribution in a broadened focal region. The development of the interaction is mapped in space and time.

ISSN:0031-9171    

DOI:10.1063/1.861698

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The theory of geometric optics in space and time varying plasmas is extended to include internal sources. The calculation proceeds by deriving the far field for a point monochromatic source. This is matched asymptotically to the geometric optics field, and the result used to generate the field due to a distributed source and the velocity space diffusion tensor for a fluctuating source. The general initial value problem for a source free plasma is solved in the geometric optics approximation, and the associated wave kinetic equation is derived.

ISSN:0031-9171    

DOI:10.1063/1.861700

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Neoclassical transport coefficients for ion and impurity species are computed in a large aspect ratio toroidal magnetic confinement system for intermediate‐to‐high collision frequencies. A large range of values of the relevant density and charge parameters is explored and terms of order (mi/mI)1/2are retained. The behavior of the transport coefficients is found to depend on the collisionality of both the ions and the impurities. A simple approximate analytic representation of these results which incorporates the correct asymptotic plateau and Pfirsch–Schlu¨ter behavior is presented. In the plateau regime, when (nI/ni)(mI/mi)1/2≪1, the inward impurity flux is found to be suppressed for experimentally obtainable plasma parameters, implying that the time scale for impurity concentration could be too long to be observable.

ISSN:0031-9171    

DOI:10.1063/1.861701

出版商:AIP    

年代:1977

数据来源: AIP