摘要:

The magnetohydrodynamic stability of diffuse, axisymmetric toroidal plasma configurations with large elongation in the direction of the axis of symmetry and large aspect ratio is investigated. In an asymptotic expansion the elongation and aspect ratio are related and both are made large. This expansion reduces the equilibrium relations in leading order to an ordinary differential equation readily susceptible to numerical solution or, in some cases, analytical solution. The same expansion procedure is also applied to the linearized stability analysis and both partial differential equations and a Rayleigh–Ritz quotient for the eigenvalues and eigenvector result. Belt pinch and doublet shapes for various current density profiles are examined for internal and external modes for both high and low &bgr; forms of the equilibrium. Growth rates and eigenfunctions for the discrete modes are given and general features of the spectrum are discussed.

ISSN:0031-9171    

DOI:10.1063/1.861850

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Methods of producing a spatially uniform, time‐averaged pressure over the surfaces of an overdense plasma confined in a spherical electromagnetic cavity are discussed. It is found that excitation of the cavity at only two eigenfrequencies is required, whereas a method suggested nearly twenty years ago requires three nondegenerate frequencies.

ISSN:0031-9171    

DOI:10.1063/1.861851

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The velocity space diffusion of ions due to ion wave turbulence is investigated experimentally using an ion wave echo. Experiments are so arranged that the streaming perturbation due to the first excited wave propagates through the localized region where the ion wave turbulence is excited, to interact with the second excited wave. The resultant second order ion wave echo damps in comparison with the case of no turbulence. The variation of the echo amplitude as the power of the spectrum of the turbulence is changed is observed, which is in quantitative agreement with the theoretical prediction. It is also revealed that the turbulent waves are far more effective than the monochromatic waves in increasing the effective collisions.

ISSN:0031-9171    

DOI:10.1063/1.861862

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A quasi‐linear theory of energy flux limitation by ion acoustic turbulence is presented. This distribution function is modeled by a Maxwellian plus an additional piece which carries a heat fluxQ. By taking the fourth moment of the Vlasov equation, one finds the anomalous thermal conductivityK≈3ve&lgr;De(e&fgr;/Te)−2. Other effects treated self‐consistently include anomalous ion heating, electron cooling, current (and associated magnetic field) generation, and enhanced inverse bremsstrahlung due to the nonthermal ion fluctuations.

ISSN:0031-9171    

DOI:10.1063/1.861863

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Numerical simulations of (i) the propagation and interactions of one-dimensional Langmuir solitons and (ii) their generation from random fluctuations by an external pump field are presented. The results of particle simulations are compared with computations based on Zakharov’s fluid model. Those computations establish that Langmuir solitons are reasonably long lived entities in one dimension and are accurately described by Zakharov’s equations, provided that resonant particle interactions are taken into account by the inclusion of a damping term. The power spectrum of the electron field fluctuations resulting from the generation of many solitons by an external pump field is compared with the theory of Kingsep, Rudakov, and Sudan.

ISSN:0031-9171    

DOI:10.1063/1.861864

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The instability generated by two ion beams of arbitrary relative strength counterstreaming parallel to an external magnetic field in the presence of a charge and current neutralizing electron background has been analyzed using the linear Vlasov equation. This analysis extends previous theories by including the effects of finite temperatures in one or both ion beams. Using the Nyquist method, marginal stability curves for arbitrary beam strengths are obtained. For the case of a weak, hot ion beam interacting with a cold plasma whistler mode, an explicit expression for the growth rate (proportional to beam strength) has been obtained. The parameters are then chosen to be applicable to parallel shock waves, modeled as two interpenetrating ion beams. It is found that at the leading edge of the shock wave unstable whistlers may stand in the shock frame for all shock Alfve´n Mach numbersMA⩾2.77. Furthermore, it is found that such unstable modes may exist for a wide range of points in the shock interior. The turbulent spectrum that results from a shock of fixed strength has a narrow bandwidth about the wavenumber of the stationary leading edge mode. These results significantly extend the previous cold theory and further support the contention that this instability is a viable mechanism for generating large amplitude turbulent structure in a collisionless shock wave.

ISSN:0031-9171    

DOI:10.1063/1.861865

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The electrostatic flute‐like normal modes were found for a collisionless loss cone plasma in a uniform magnetic field with density varying sinusoidally in one direction in space. A local method, appropriate tokL≫1, wherekis the wavenumber andLis the scale length, and a nonlocal method, appropriate tokL≲1, where both used; the ion Larmor radiusaiwas not assumed to be small. The usual drift cone mode was found whenai≪L; other instabilities were found forai≳L. In principle, the methods could be applied to other configurations of plasma.

ISSN:0031-9171    

DOI:10.1063/1.861866

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The local dispersion relation for the lower‐hybrid‐drift isntability is derived in a fully self‐consistent manner including the finite‐beta effects associated with (a) transverse electromagnetic perturbations (&dgr;B≠0), and (b) resonant and nonresonant h&slash;B0electron orbit modifications. Moreover, the analysis is carried out for arbitrary values of local &bgr;=8&pgr;n(Te+Ti)/B02,Te/Ti, &ohgr;2pe/&ohgr;2ce, andVE/vi. (Here,VEis the cross‐field E×B velocity, andviis the ion thermal speed.) For all parameter regimes studied, the net effect of finite plasma beta is to reduce the maximum growth rate &ggr;mof the lower‐hybrid‐drift instability. The details, however, vary, depending on plasma parameters. For example, ifTe≪TiandVE<vi, then the maximum growth rate is reduced by a factor (1+&bgr;i/2)−1/2, relative to the value obtained when &bgr;i=8&pgr;nTi/B20→0. On the other hand, forTe≈Ti, there exists a critical value of plasma beta (&bgr;cr) such that the lower‐hybrid‐drift instability is completely stabilized (&ggr;<0) for &bgr;≳&bgr;cr.

ISSN:0031-9171    

DOI:10.1063/1.861867

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Magnetic shear is shown to stabilize the lower hybrid drift wave when the shearing distance isLs<Ln(ai/Ln+Ln/ai), whereLn≡dlnn/dxis the density gradient scale length andaiis the ion gyroradius.

ISSN:0031-9171    

DOI:10.1063/1.861868

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A new type of high‐power pinch apparatus consisting of disk electrodes was developed and diagnostic measurements to study its mechanism of dense plasma production have been made. The collapse fronts of the current sheets are well organized and dense plasma foci are produced on the axis with radial stability in excess of 5 &mgr;sec. A plasma density greater than 1018cm−3is determined with Stark broadening and CO2laser absorption. Essentially complete absorption of a high‐energy CO2laser beam has been observed. A plasma temperature of approximately 1 keV is measured with differential transmission of soft x rays through thin foils. The advantages of this apparatus over the coaxial plasma focus are improvements in (1) plasma volume, (2) stability, (3) containment time, (4) access to additional heating by laser or electron beams, and (5) the possibility of scaling up to a multiple array for high‐power operation.

ISSN:0031-9171    

DOI:10.1063/1.861869

出版商:AIP    

年代:1977

数据来源: AIP