摘要:

In a high‐beta plasma the so‐called modified‐two‐stream instability, which results from strongly magnetized electrons drifting relative to unmagnetized ions across a homogeneous magnetic field, is misnamed because the mode is highly kinetic, particularly when the relative streaming velocity exceeds the Alfve´n speed of the plasma. This kinetic cross‐field streaming instability is investigated in detail, examining the effect of the electromagnetic terms and the stability boundaries in both low‐ and high‐beta plasmas. An approximate dispersion relation showing the relation of this mode to the whistler is derived and solutions of it are compared with those obtained from the exact dispersion relation. The kinetic mode, unlike the usual modified‐two‐stream instability, is not stabilized by electromagnetic effects when the relative electron–ion drift speed exceeds the Alfve´n speed.

ISSN:0031-9171    

DOI:10.1063/1.864285

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Many radio‐frequency heating methods involve conversion of an incoming wave to another mode which only propagates within the plasma and is ultimately damped. A method previously used to consider electron cyclotron heating by the O mode is extended to other mode conversion phenomena.From the properties of the dispersion relation in the neighborhood of the mode conversion point, differential equations for the mode amplitudes are constructed, in a well‐defined way, which give energy conservation in the absence of damping. An analytic solution gives the transmission and conversion coefficients in terms of parameters defining the local behavior of the dispersion relation. The technique is applied to a number of problems, showing that they can all be solved by elementary algebraic manipulations of the local dispersion relation. The phenomenon of electron cyclotron emission also falls rather naturally into this mode conversion picture. It is also suggested that the method of dealing with cyclotron emission may have some relevance to the more general problem of energy transport across a magnetic field. The technique, therefore, brings together into a unified theory a number of problems which have been treated by diverse, and usually more complicated, mathematical techniques in the existing literature.

ISSN:0031-9171    

DOI:10.1063/1.864286

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The linear instability of pairwise‐coalescing magnetic islands is studied analytically and numerically using incompressible ideal magnetohydrodynamics. An energy principle calculation shows that for small values of the island widthw, the growth rate of the instability is proportional tow3/2. Numerical simulations are presented giving detailed information about the mode structure.

ISSN:0031-9171    

DOI:10.1063/1.864287

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The nonlinear evolution of the transverse instability of plane envelope soliton solutions of the nonlinear Schro¨dinger equation is investigated. For the case where the spatial derivatives in the two‐dimensional nonlinear Schro¨dinger equation are elliptic a critical transverse wavenumber is found above which the soliton is stable. Application of the multiple time scale method near this critical transverse wavenumber gives a dynamical equation for the nonlinear evolution of the transverse instability. Nonlinearity is found to enhance the growth of the linearly unstable mode. The results are discussed in connection with soliton collapse.

ISSN:0031-9171    

DOI:10.1063/1.864288

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A method of analyzing ergodic magnetic fields is given, including a generalization of magnetic coordinates to such fields. The results of this analysis can be used in existing Monte Carlo codes to assess the enhanced transport associated with imperfect surfaces. The Hamiltonian for a general magnetic field is given as part of this analysis.

ISSN:0031-9171    

DOI:10.1063/1.864289

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

It is shown that minimum energy equilibria can be constructed with anyq(inverse rotational transform) profile such that 1/qis continuous. These equilibria are stable to both ideal magnetohydrodynamic (MHD) and tearing modes. In particular, explicit equilibria are presented which have a local minimum inqbut are nevertheless stable.

ISSN:0031-9171    

DOI:10.1063/1.864264

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Magnetohydrodynamic equilibrium and stability studies of field‐reversed configurations are presented. Experimentally realistic equilibria are calculated numerically for a plasma inside a conducting cylinder. Stability studies indicate that equilibria ranging from elliptical to highly racetrack‐shaped are all unstable to the internal tilting mode.

ISSN:0031-9171    

DOI:10.1063/1.864290

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Two‐dimensional field‐reversed equilibria bounded by a conducting cylinder are computed. The computation is made possible by using a global constraint and by using a computational algorithm that is protective of the initial guess. A pressure profile is used that has sufficient generality to match experimentally produced configurations. It is found that for some choices of separatrix radius and separatrix beta, no equilibria exist. The reasons for loss of equilibrium are discussed and an example of a configuration near loss of equilibrium conditions is given.

ISSN:0031-9171    

DOI:10.1063/1.864291

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A computational and analytical study of the nonlinear evolution of single‐helicity, resistive, current‐driven modes in the reversed‐field pinch utilizing the single‐fluid magnetohydrodynamic approximation is presented. In the start‐up phase it is found that an off‐axis current peak can be anomalously dissipated by globally reconnecting current‐driven modes. The reconnection is seen to be well described by the Kadomtsev reconnection model, which is directly applied to the reversed‐field‐pinch regime. During the sustainment phase of the discharge, stable profiles are driven unstable by transport processes and restabilized by the resulting current‐driven instabilities. The dynamics of the toroidal field is of fundamental importance in the evolution of these modes. The reversed‐field‐pinch profile is restabilized by two successive global reconnections: the first removes the rational surface; the second restores it. It is also found that magnetic reconnection can occur in the reversed‐field pinch without a linear phase. Although the interaction of instabilities with different helicities is not directly investigated, the importance of this phenomenon in the reversed‐field pinch is discussed.

ISSN:0031-9171    

DOI:10.1063/1.864253

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Rotational instabilities in rigidly rotating field‐reversed configuration (FRC) equilibria are studied using a quasineutral hybrid simulation code. We observe unstablem=2 modes at levels of ion rotation below instability thresholds predicted by finite‐Larmor‐radius fluid theory. Nonlinear effects are found to reduce the growth rate and lower the real frequency of them=2 mode at large amplitude. Instabilities withm>2 have been observed for strongly reversed cases. It is also found that growth rates for these instabilities can be reduced by increasing the ratio of the plasma radius to the ion Larmor radius.

ISSN:0031-9171    

DOI:10.1063/1.864254

出版商:AIP    

年代:1983

数据来源: AIP