摘要:

Nonlinear electron plasma oscillations are investigated in the wavebreaking regime where collective energy is converted into random energy. The Lagrangian description of the electrons is extended beyond fluid element orbit crossing, thereby exposing the essential physics of wavebreaking and permitting simple analytical interpretation of it. In driven cold inhomogeneous plasma a region of large resonant oscillations decays by producing energetic electrons which escape into the less dense plasma. The maximum energy of the fast electrons produced during the driver period in which the first wave breaks is much larger than the energy of an electron oscillating freely in the driver field. The total energy of the fast electrons exceeds that supplied the system by the driver in a period and can be a significant fraction of the total energy in the oscillations at the onset of wavebreaking.

ISSN:0031-9171    

DOI:10.1063/1.861300

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A closed form solution for the electromagnetic field of a charged particle passing through a medium of finite conductivity &sgr; is presented. The wake field of the particle extends over a region of a characteristic length 1/&mgr;0&sgr;v, and is confined behind a plane which contains the particle. The electric lines of force reverse themselves, indicating current neutralization by the changing magnetic field. It is noted that the induced current around the charge has no dc component.

ISSN:0031-9171    

DOI:10.1063/1.861301

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The synchrotron radiation spectrum is calculated for a relativistic nonneutral plasma column that rotates about an axis of symmetry aligned parallel to a uniform applied magnetic fieldB0eˆz. The applied magnetic field provides radial confinement of the electrons, and the electron density is assumed sufficiently low so that equilibrium self‐fields have a negligible effect on the particle trajectories (&ohgr;2p/&ohgr;2c≪1, where &ohgr;pis the electron plasma frequency and &ohgr;cis the electron cyclotron frequency). The analysis is carried out for the general class of radially confined equilibria described by equilibrium distribution functions of the formf0e(x,p) =F(H)G(P&Vthgr;) &dgr; (pz), whereHis the energy,P&Vthgr;is the canonical angular momentum, andpzis the axial momentum. The detailed form of the emission spectrumIl(&ohgr;) exhibits a sensitive dependence on the choice of distribution functionsF(H) andG(P&Vthgr;). The characteristics of the emission spectra for hollow electron layers are quite different from the emission spectra obtained when the electron density is peaked on axis. Since the influence of equilibrium self‐fields on the particle trajectories is neglected in the present analysis, the results can also be applied to the synchrotron emission from rotating neutral plasma columns in which there is over‐all charge neutrality.

ISSN:0031-9171    

DOI:10.1063/1.861275

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Resonant absorption has been simulated for radiation of energy densityE20/4&pgr;nTranging from much less than to somewhat greater than unity. Characteristic features of the absorption process are an absorption efficiency of approximately 50%, generation of suprathermal particles, and strong modification of the density profile in the vicinity of the critical density. The latter effect, the appearance of a finite density variation over the distance of a few Debye lengths, is forced by strong gradients in the plasma wave intensity and electron temperature. Such a density discontinuity greatly enhances the range of incidence angles for which resonance absorption is effective and decreases the effects of the oscillating two‐stream and ion‐acoustic decay instabilities.

ISSN:0031-9171    

DOI:10.1063/1.861276

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Neoclassical transport coefficients are computed in a large aspect ratio toroidal magnetic confinement system in order to examine the transition between the plateau and Pfirsch–Schlu¨ter regimes. The calculation employs a hybrid collision operator combining Krook and pitch angle scattering terms with the identical particle collision frequency taken to be a function of velocity which is determined from a fit to known exact results for classical transport. A simple approximate analytic form is presented which incorporates both these results and the results of Hinton and Rosenbluth for lower collision frequencies.

ISSN:0031-9171    

DOI:10.1063/1.861277

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Phase space density granulations (or ’’clumps’’) have been observed in a one‐dimensional computer simulation plasma. Fluctuations were initially distributed over a wide range of velocities in a Maxwellian plasma. Clumps were observed at the thermal velocity 150 plasma periods later, long after the fluctuations should have decayed down to the thermal equilibrium level according to conventional theory. Within the accuracy of the simulation, the phase space density correlation function obtained from the simulation agrees well with the theoretical expression for clumps.

ISSN:0031-9171    

DOI:10.1063/1.861278

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Numerical simulations are used to investigate plasma heating by the oscillating, two‐stream instability at moderate amplitude. Substantially all the absorbed electromagnetic energy goes into production of a suprathermal electron population. A simple functional form describes the shape of the suprathermal distribution function, which is proportional tov−2over a wide velocity range. This holds for a wide range of driving field amplitude. The multiplicative constant increases linearly with time within a simulation. The plasma electric field spectrum has a characteristic power law shape, which is interpreted as the result of the waves coming into quasi‐thermal balance with electrons near their phase velocity. The results for the electron distribution function are in qualitative agreement with experiments by Dreicer, Ellis, and Ingraham, but they disagree with those of Mizuno and De Groot and of Porkolab.

ISSN:0031-9171    

DOI:10.1063/1.861279

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The possibility of heating collisionless toroidal plasmas to high temperatures by means of linear wave absorption above the lower hybrid frequency is discussed. This absorption is mainly due to electron Landau damping and ion damping is neglected. Two methods of heating are considered, propagating a wave across the plasma column and exciting toroidal modes. WKB solutions of the first method show that the incident wave must be within a narrow range ofkzfor its energy to be uniformly deposited into the plasma. Toroidal mode solutions indicate that this band ofkzmay be significantly widened by lowerkzwaves which drive slightly damped toroidal modes. The conditions onkzfor accessibility and heating are calculated and the advantages of such an approach are discussed.

ISSN:0031-9171    

DOI:10.1063/1.861280

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

An extraordinary incident wave propagating along the major radius through the ST tokamak plasma is used to generate a second harmonic wave at the upper hybrid layer. Remote polarization measurements of the harmonic yield the poloidal magnetic field profile. The estimated over‐all error in the measurement of the rotation angle of the total magnetic field is ≃0.3×10−2rad. Further improvements in the accuracy of the measurements which are required to specify the current density profile unambiguously are discussed.

ISSN:0031-9171    

DOI:10.1063/1.861281

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Although the questions of whether all the dynamical states are accessible (’’observability’’) and amenable to control (’’controllability’’) play central roles in control science and engineering, these have been completely ignored in the literature of control of plasma instabilities. These problems are discussed and the general conclusion is that any plasma instability of discrete spectrum is completely observable and controllable with a few, but, most often, a single pair of, suitably located point sensor and suppressor.

ISSN:0031-9171    

DOI:10.1063/1.861282

出版商:AIP    

年代:1975

数据来源: AIP