摘要:

The effect of the magnetic shear on the current‐driven ion cyclotron instability has been studied. Taking into account the asymmetry introduced by the external current, an analytical theory to study the nonlocal behavior of this instability is given. The main consequences of the magnetic shear are to (i) localize the instability in space and (ii) reduce the growth rates in general. The damping influence of shear arises in two distinct ways; (a) a damping rate directly proportional to the shear strength, and (b) a damping rate (due to the nonlocal nature of the dispersion relation) not explicitly dependent on shear which can be quite strong for above marginal currents. Shear makes this instability more coherent by reducing the band of the perpendicular wavelengths which is unstable. The general physics of this instability and the parametric dependences of the growth rates are studied and marginal stability curves given.

ISSN:0031-9171    

DOI:10.1063/1.863661

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A theory of drift wave turbulence is presented based on a low‐density gas of drift wave solitons. The Gibb’s ensemble for the ideal gas is used to calculate the dynamical scattering form factorS(k,&ohgr;). In contrast to renormalized turbulence theory, the spectrum has a broad frequency component with &Dgr;&ohgr; proportional to the fluctuation level &dgr;ne/n0at fixedkand peaks at a frequency &ohgr;≳kyvde.

ISSN:0031-9171    

DOI:10.1063/1.863662

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The effect of a stochastic magnetic field on the evolution of a long wavelength tearing mode is investigated analytically. A near Gaussian statistical closure approximation is used to obtain renormalized statistical equations from the fluid equations. The stochastic magnetic field is found to induce a turbulent electron dissipation. For typical tokamak discharge parameters, this turbulent dissipation both broadens the current layer of the mode and leads to a growth rate which, for fluctuation levels ⟨(&dgr;B/B)2⟩ as small as 10−8, is significantly larger than the classical resistive growth rate.

ISSN:0031-9171    

DOI:10.1063/1.863663

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Relaxation of plasmas via turbulence is treated by the use of a maximum entropy principle. The relaxed states are always stable to ideal modes. Taylor’s theory of field reversal is extended to finite pressure plasmas and given a rigorous support by using symmetries in the equations to determine preferred conservation laws. Relaxed states of field‐reversed &Vthgr; pinches are predicted, some with self‐reversal of the magnetic field.

ISSN:0031-9171    

DOI:10.1063/1.863664

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The neoclassical transport theory for tokamak plasmas in the plateau to Pfirsch–Schlu¨ter regimes is extended to cases in which the parallel flow can become comparable to the ion thermal velocity. Important changes are found in the qualitative structure and the quantitative predictions of the theory. Solutions for both pure and impure plasmas in the plateau regime are obtained.

ISSN:0031-9171    

DOI:10.1063/1.863665

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The nonadiabatic part of the particle response to low‐frequency electromagnetic modes with long parallel wavelengths is discussed. Analytic approximations to the kernels of the integrals that relate the amplitudes of the perturbed potentials to the nonadiabatic part of the perturbed density in an axisymmetric toroidal configuration are presented and the results are compared with numerical calculations. It is shown that both in the plane slab and in toroidal geometry the kernel contains a logarithmic singularity. This singularity is associated with particles with vanishing parallel velocity so that, in toroidal geometry, it is related to the behavior of trapped particles near their turning points. In contrast to the plane slab, in toroidal geometry this logarithmic singularity is mainly real and associated with nonresonant particles. Apart from this logarithmic term, the kernel contains a complex regular part arising from resonant as well as from nonresonant particles.

ISSN:0031-9171    

DOI:10.1063/1.863666

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The coalescence of two spheromaks is described using the quasi‐ideal model of reconnection. Nonaxisymmetric effects are found to play an important role in general. Possible applications of repeated coalescence are studied, including heating the spheromak plasma, building up a large spheromak from smaller ones, and maintaining a spheromak in steady state. The analysis suggests that coalescence experiments could also provide a valuable method for studying magnetic field relaxation.

ISSN:0031-9171    

DOI:10.1063/1.863667

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A diffusion effect has been measured on a time‐of‐flight velocity distribution measurement of a laser‐produced plasma. After allowing for this effect, a good fit to a nondisplaced Maxwellian is obtained. The fit was made to the total ion signal. Retarding voltage measurements show that most of the ions are triply ionized.

ISSN:0031-9171    

DOI:10.1063/1.863636

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Analytic models are derived for two important processes in laser‐generated shock‐wave phenomena: preheat energy deposition by suprathermal electrons and hydrodynamic shock attenuation. Predictions of the models are compared with available experimental data and other theoretical treatments, including extensive hydrodynamic code calculations, and in all cases good agreement is found. Combination of the models permits calculation of the maximum shock pressure attainable under any given set of direct irradiation conditions. Analytic expressions for optimum laser pulse length, target thickness, and laser intensity as functions of laser energy are also derived.

ISSN:0031-9171    

DOI:10.1063/1.863637

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Stability properties of a charged beam propagation through a relativistic hollow electron beam are investigated, in connection with present experimental applications in the collective particle accelerator. The stability analysis is carried out for long axial wavelength and low‐frequency perturbations. A closed algebraic dispersion relation for coupled transverse oscillations is obtained for the solid and hollow beams with sharp‐boundary density profiles. One of the most important features in the analysis is that the typical growth rate of the transverse oscillation is of the order of the hollow beam diocotron frequency &ohgr;D, thereby severely limiting the solid beam propagation through a relativistic hollow electron beam. Particularly, for a solid beam with a small radius, the fundamental mode perturbation (i.e., the dipole oscillation) is the most unstable mode.

ISSN:0031-9171    

DOI:10.1063/1.863638

出版商:AIP    

年代:1982

数据来源: AIP