摘要:

The rotation of a toroidally confined plasma about its magnetic axis due to resistive diffusion is studied by means of a single fluid model in which the only dissipation occurs through a small scalar resistivity. The time evolution of the rotation is examined by considering the resistivity as inducing first‐order time variation on a dissipationless steady state. The known instability of flows with small rotational velocity to rapidly speed up toward a critical speed is confirmed; more importantly, it is found that a shock which develops at the critical speed stabilizes the flow, so that the ultimate state of the system is characterized by steady rotation with a very weak shock front directed radially inward from the magnetic axis. The outward flux of plasma in this state is found to be essentially the Pfirsch‐Schlu¨ter flux enhanced by a factor of the square root of the aspect ratio.

ISSN:0031-9171    

DOI:10.1063/1.1693436

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The deconfining ponderomotive force exerted by an intense electromagnetic wave on a linearly inhomogeneous plasma layer has been analytically investigated. Since the ponderomotive force maximizes near the region where the dielectric constant&egr;′ → 0, an exact solution of the wave equation is required for a correct estimate of the maximum force. For the case of oblique incidence with the electric vector in the plane of incidence, the solution of the exact wave equation leads to an interesting resonance effect which predicts a force higher than that obtained by earlier workers using a WKB procedure. Physically, this enhanced ponderomotive force arises because of the large nonuniform longitudinal fields that are generated in the region&egr;′ ≈ 0for this geometry.

ISSN:0031-9171    

DOI:10.1063/1.1693437

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Reflection and penetration of ap‐polarized electromagnetic wave obliquely incident on a plasma half‐space is investigated. The perturbed plasma is treated by use of the linearized relativistic Vlasov equation. Electrons are assumed to be specularly reflected from the boundary. The Laplace transform technique, recently employed by Ozizmir, is used to obtain the field solutions in the plasma. These field solutions consist of a transverse and a longitudinal part. Power reflection and transmission coefficients are also obtained.

ISSN:0031-9171    

DOI:10.1063/1.1693438

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A plasma configuration with cylindrical symmetry is studied, containing axial and azimuthal magnetic fields and radial electric field, with arbitrary radial variation. The particle motion is parameterized by three exact action invariants: radial action, canonical angular momentum, and canonical axial momentum; in the limit of small gyroradius they are equivalent to magnetic moment, radial guiding‐center position, and parallel velocity. The perturbed Vlasov‐Maxwell equations lead to a set of normal modes, which can interact resonantly with the particles. The quantum rate equations for this interaction, together with the laws for conservation of energy, angular momentum, and axial momentum, lead (in the classical limit) to a Fokker‐Planck equation in action space for the particles, and to an equation of evolution for mode energy. These coupled kinetic equations satisfy anHtheorem, which implies a monotonic approach to a canonical distribution: a rigid‐rotor distribution for particles, and a generalized Rayleigh‐Jeans distribution for the modes. This asymptotic state may, however, be unconfined. The quantum transition probability is deduced from a classical calculation of emissivity. Explicit expressions are obtained for the mode growth rate and for the particle diffusion tensor. Finally, the Vlasov conductivity kernel is deduced from the growth rates, by the use of the Kramers‐Kronig relations.

ISSN:0031-9171    

DOI:10.1063/1.1693439

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The results of a theory‐experiment comparison of the absolute electromagnetic wave backscatter from a neutral gas dominated turbulent argon arc plasma jet are reported. The study is carried out at 16 GHz, for various aspect angles and covers a range of rms electron density fluctuations extending beyond critical. The backscatter power is measured using a homodyne detection system. The calculation, based on the unmodified Born scattering model, consists of a volume weighting of the turbulent plasma properties,⟨&dgr;ne2andS(k), by the antenna illumination. The determination ofS(k), the three‐dimensional spectral density function, makes use of the measured space‐time correlation function and frequency spectrum of electron density fluctuations, Taylor hypothesis, and a three‐dimensional MacDonald function analysis. The Born theory is found to describe the backscatter within about 3 dB right up to critical. This result is thought to be due in part to attenuation of the coherent antenna field by large density fluctuations being roughly compensated for, both by decreasing wavenumber and by higher order multiple scattering effects.

ISSN:0031-9171    

DOI:10.1063/1.1693440

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A simple model for calculating scatter from a turbulent medium has been applied to a computer experiment with good results. The proposed calculation is a modification of a first‐order Born calculation that accounts for attenuation due to absorption and scatter by energy conservation. Such a nonrigorous approach requires experiments to specify the scatter attenuation in a phenomenological way. The exact computer calculations by Hochstim and Martens constitute such an experiment.

ISSN:0031-9171    

DOI:10.1063/1.1693441

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The development of an electron beam‐plasma instability beyond the stage described by quasilinear theory has been investigated by means of kinetic equations for waves and particles which include the effects of spontaneous emission and scattering of waves. Characteristic times for the formation of a high‐energy tail have been computed, which at late times may extend significantly beyond the original beam velocity. Qualitative agreement is obtained with experiments.

ISSN:0031-9171    

DOI:10.1063/1.1693442

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The Coppi‐Perkins theory of collisional drift waves in low‐&bgr; plasmas is extended to plasmas containing ions of two different types. Recent experiments call for such an extension. Before discussing the general results, the specialization to the usual plasma shows the destabilizing effect of a high ionic charge and of an electron temperature exceeding the ion temperature. As an application of the obtained criterion of marginal stability the average ion mass is computed and compared to the intuitive linear formula, based only upon concentrations. Under present‐day conditions almost no difference is detected, but for future experiments with higher temperatures and higher mass ratios the correct formula is shown to give less stable results than the intuitive one at the same relative concentration. This is also true for lower densities and shorter wavelengths. The discrepancies can become quite important.

ISSN:0031-9171    

DOI:10.1063/1.1693443

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A simple procedure for numerically obtaining the solution of a linear, differential boundary‐value problem is presented. For annth‐order equation, the technique requires the solution ofninitial‐value problems. The solution of the boundary‐value problem is then a linear combination of these solutions. The technique has very attractive features that should make it a convenient method for studying a variety of stability problems in bounded systems. As an example of these applications, the initial stability of the inertial containment device proposed by Hirsch is examined. It is found that the particular model studied is marginally stable. The results are compared with computer simulation studies of the device.

ISSN:0031-9171    

DOI:10.1063/1.1693444

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The nonlinear Fokker‐Planck equation describing the relaxation of the fully ionized gas is solved by the Mott‐Smith method. The relaxation time obtained using the lower‐moment equations is found to agree with the Spitzer self‐collision time.

ISSN:0031-9171    

DOI:10.1063/1.1693445

出版商:AIP    

年代:1971

数据来源: AIP