摘要:

Agreement between data from a plasma rail gun as analyzed by a time‐of‐flight technique and predicted by snowplow theory indicates that there is no necessity for any theory of drag force in the gun and seems to indicate that one theory for drag force which also accounts for the conduction of electrical current into a moving plasma should be re‐examined.

ISSN:0031-9171    

DOI:10.1063/1.1693291

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The problem of laser energy addition to a nonuniform one‐dimensional plasma is considered. The object is to study plasmas which may achieve temperatures and densities of interest for application to controlled thermonuclear reactions. The advent of the nanosecond and picosecond lasers makes it possible to consider the heating of stationary, nonthermally conducting plasmas with a nonuniform density distribution in which only the electrons are heated. The solutions show that for a wide range of relevant parameters these assumptions are valid. The temperatures that can be produced are of interest in controlled thermonuclear reactions. Depending on the steepness of the density gradient, either wavelike or simultaneous heating is produced. Also, the temperature distribution is very much nonuniform and can significantly affect the subsequent dynamics of the plasma.

ISSN:0031-9171    

DOI:10.1063/1.1693292

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A numerical solution of the equations for unstable electrostatic plasma waves propagating in a uniform infinite plasma with a weak beam is performed. Space dependent variables are Fourier transformed and the computations are done first with only one and then with two harmonics included. In both cases the first harmonic electric field reaches a maximum amplitude and thereafter oscillates periodically, the period being different in the two cases. Thus, the time evolution of the field depends strongly on the presence of the second harmonic. The second harmonic electric field itself has negligible amplitude compared with the fundamental but the corresponding perturbed distribution functions are comparable in the vicinity of the wave resonance. In the frame of the background plasma the frequency of the first harmonic electric field is close to the plasma frequency&ohgr;pbut the nonlinearly generated second harmonic frequency is2&ohgr;p. Because of this it is found that the wave‐wave interaction terms are important and resonant processes occur. The neglect of such terms in quasilinear theory is questioned.

ISSN:0031-9171    

DOI:10.1063/1.1693293

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The effects of transverse velocity shear on the low‐frequency stability of a plasma are examined theoretically for a low‐&bgr; resistive plasma in a uniform magnetic field. Cylindrical geometry is used and the velocity shear is introduced by a nonuniformE × Brotation. Both numerical and analytic methods are used. The principal analytic result is a dispersion relation for instabilities caused by a thin velocity shear layer. This dispersion relation describes theQmachine edge oscillation, which is identified either as a Kelvin‐Helmholtz instability or as a velocity‐shear analog of the resistive drift wave, depending on the parallel wavelength. The numerical results show that properties of instabilities observed in several experiments agree reasonably well with theory. The effect of velocity shear on the drift instability is to make it into either a local or nonlocal type of normal mode.

ISSN:0031-9171    

DOI:10.1063/1.1693259

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A nonlinear analysis of collisional drift waves is presented in which a systematic expansion is made in powers of the wave amplitude. The two‐fluid equations are used, including the effects of resistivity, viscosity, and thermal transport. The result, for the wave amplitude as a function of magnetic field in the linearly unstable region close to marginal stability, agrees reasonably well with experiment.

ISSN:0031-9171    

DOI:10.1063/1.1693260

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The Krylov‐Bogoliubov‐Mitropolsky method is applied to the study of the interaction among three extraordinary waves propagating perpendicularly to a uniform magnetic field in a hot electron plasma. The frequency and wavenumber of the three waves satisfy the conditions&ohgr;1 + &ohgr;2 = &ohgr;3and&kgr;1 + &kgr;2 = &kgr;3. When the external magnetic field is small, the first and the third wave show a transverse character and the second wave shows a longitudinal character; in the case of a zero magnetic field, they reduce, respectively, to transverse and longitudinal waves. In the absence of a magnetic field the analysis shows a mechanism, through which the energy of a longitudinal wave may be converted into the energy of a transverse wave.

ISSN:0031-9171    

DOI:10.1063/1.1693261

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A theory is given for treating large amplitude disturbances to ion flow in a low‐pressure positive column using a characteristics method of solution.

ISSN:0031-9171    

DOI:10.1063/1.1693262

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Experiments have shown the appearance of “nonclassical” resistivity, higher than that predicted by the known transport theory based on electron‐ion collisions, in magnetically confined plasmas where the electron gyrofrequency is larger than the Langmuir frequency and the electric field is well below the runaway threshold. A theoretical interpretation of the anomalous resistivity onset is proposed observing that (at long but finite mean free paths) nonresonant modes, associated with the effects of electron‐electron collisions, are excited when the electron flow velocity along the magnetic field is roughly larger than the ion sound‐wave velocity. The magnitude of anomalous resistivity is then discussed in relation with the nonlinear effects of resulting fluctuations and of related modes with wavelengths shorter than the mean free path. A comparison between several experiments on plasma confined in different stellarator and tokamak configurations is given. The differences in physical regimes that lead to various mechanisms for the appearance of “nonclassical” resistivity and the relationship with anomalous diffusion are pointed out.

ISSN:0031-9171    

DOI:10.1063/1.1693264

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The effect of Coulomb collisions on the growth of the instability of monoenergetic beams and beams of finite initial velocity spread in a plasma has been investigated experimentally. The results are compared with existing theories and with computations based on a beam with Lorentzian distribution function. It is shown that the instability is suppressed by collisions if the beam has a sufficiently large velocity spread in agreement with the prediction of Ascoli and Singhaus and that their stability criterion is valid over a larger parameter range than had previously been assumed. Evidence is presented for a self‐quenching of the instability of an initially monoenergetic beam due to the combined effect of collisions and the smearing out of the beam distribution function by the unstable waves.

ISSN:0031-9171    

DOI:10.1063/1.1693265

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A gun‐injected hydrogen plasma was contained in a toroidal octupole magnetic field. The plasma motion due to the changing magnetic field was studied and compared to a model based on the flux invariance of the motion. For early injection (while the field was rising) there was a strong motion toward the multipole rods while for late injection the motion was toward the wall. Magnetohydrodynamic theory shows that the plasma becomes unstable near the separatrix due to this motion. Although fluctuations were observed in this region, the plasma was found to be distributed stably.

ISSN:0031-9171    

DOI:10.1063/1.1693266

出版商:AIP    

年代:1971

数据来源: AIP