摘要:

It is shown that a distribution of electrons in resonance with traveling waves, but colliding with background distributions of electrons and ions, evolves to a steady state. Previously, the existence of such solutions had been assumed, but not proved, in numerical and other calculations. Details of the steady state are given analytically in the asymptotic limit of high electron energy and are compared with numerical solutions. The asymptotic analytic solution may be useful for quickly relating emission data to likely excitations and is more reliable than conventional numerical solutions at high energy. A method of improving numerics at high energy is suggested.

ISSN:0031-9171    

DOI:10.1063/1.865352

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Whistler mode electron‐cyclotron resonance heating (ECRH) has been performed simultaneously with whistler mode electron‐cyclotron emission measurements on an axisymmetric magnetic mirror plasma. Results presented include a study of the early plasma startup phase and two instability phases, one believed to be caused by a whistler instability and another by magnetohydrodynamic (MHD) flute instability. Enhanced microwave emission at frequencies below the midplane electron‐cyclotron frequency has been correlated with enhanced electron endloss during the whistler instability. Cyclotron emission spectra during the startup phase match predictions for a ‘‘sloshing electron’’ type distribution based on numerical modeling. This distribution also agrees with anisotropic distributions resulting from electron‐cyclotron heating as predicted by Fokker–Planck computer simulations. Experimentally measured heating rates show good agreement with simplified analytical models based on stochastic heating.

ISSN:0031-9171    

DOI:10.1063/1.865353

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An asymptotic model is developed to study magnetohydrodynamic equilibria in toroidal systems with a helical magnetic axis. Using a characteristic coordinate system based on the vacuum field lines, the equilibrium problem is reduced to a two‐dimensional generalized partial differential equation of the Grad–Shafranov type. A stellarator‐expansion free‐boundary equilibrium code is modified to solve the helical‐axis equations. The expansion model is used to predict the equilibrium properties of toroidal asperator devices. Numerically determined flux surfaces, magnetic well, transform, and shear are presented. The equilibria show a toroidal Shafranov shift.

ISSN:0031-9171    

DOI:10.1063/1.865354

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Spectroscopic measurements on the ZT‐40M reversed field pinch [submitted to Fusion Tech.] discharge are reported. Specifically, the impurity content,Zeff, recycling behavior, ion temperature, and propagation of magnetohydrodynamic modes in the edge are addressed. The importance of the plasma–wall interaction in ZT‐40M, operated without limiters, is demonstrated.

ISSN:0031-9171    

DOI:10.1063/1.865355

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Internal magnetic field measurements are used to study the reconnection process near the ends of a low‐compression field‐reversed theta pinch. The measurements indicate that the addition of independently driven magnetic mirror coils at the ends are effective in inducing rapid reconnection and in minimizing plasma losses out the ends. Fast reconnection leading to the formation of a chain of magnetic islands along the length of the coil is observed on a time scale of a 100 nsec. These islands coalesce on a time scale of 1–2 &mgr;sec. Measured values of the resistivity are two orders of magnitude greater than classical during the implosion phase. The resistivity during the equilibrium phase is four times the classical value. Axial contraction and then=2 rotational instability are not observed to occur in these experiments. Sudden termination of the configurations is thought to be caused by rapid loss of the internal field. This flux dissipation may be a consequence of electron cooling by the crossing of a radiation barrier. An oxygen impurity concentration of 2% is enough to account for the power dissipated during the collapse.

ISSN:0031-9171    

DOI:10.1063/1.865356

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The physical processes involved in the formation of a spheromak are studied. Using one‐fluid axisymmetric resistive magnetohydrodynamic equations together with a temperature equation, investigations of the essential physics aspects of the formation specifically for the new Maryland Spheromak (MS) [J. Antoniades, C. Chin‐Fatt, A. DeSilva, G. Goldenbaum, R. Hess, and R. Shaw, inProceedingsoftheSixthU.S.SymposiumonCompactTorusResearch, Princeton, 1984 (Princeton Plasma Physics Laboratory, Princeton, NJ, 1985), p. 65] have been performed. These studies elucidate the role of differential rotation in accelerating the penetration of toroidal fieldB&fgr;and in forcingI≡ rB&fgr;to be a flux function. Another important aspect of the formation is the magnetic reconnection that occurs at the X point between the two reversal coils. A strong toroidal current is generated by the reconnection, and the X point is converted into an O point that finally becomes the magnetic axis of the spheromak. In this latter phase of reconnection, the plasma is heated very strongly. Studies have also been done on the effect of the difference in phase and time scales for the reversal andIzbanks for the purpose of optimization. The effect of radiation from carbon and oxygen is examined and found to have very little effect on the proposed formation scheme. The results are also relatively insensitive to changes in the anomalous electron thermal conduction models used.

ISSN:0031-9171    

DOI:10.1063/1.865357

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The stability of the transverse monopole oscillation is considered in contrarotating, reciprocally pinched, cylindrically symmetric beams bunched in the moving direction. The problem is reduced to coupled and time‐dependent ordinary second‐order linear differential equations for the perturbed beam envelope functions. The equations are solved exactly and the self‐consistent stability condition for transverse monopole oscillations is derived to first order.

ISSN:0031-9171    

DOI:10.1063/1.865358

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

This Brief Communication is concerned with establishing the effect of the presence of a third diffusing component on the onset of convection in a horizontal fluid‐saturated porous layer. The linear stability analysis procedures used in double diffusion are extended to take into account a third diffusing constituent. As a result, general expressions for the various stability boundaries are obtained. The presence of a third diffusing component with small diffusivity can seriously alter the nature of the convective instabilities in the system. For the most part, the findings of the present study for a porous layer exhibit similar behavior to the results reported by Griffiths [J. Fluid Mech.92, 659 (1979)] for triple diffusion in a layer of classical fluid. However, when heat is one of the three diffusing components, the porosity of the porous medium has a considerable effect on the marginal stability boundary for oscillatory convection.

ISSN:0031-9171    

DOI:10.1063/1.865359

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The interesting paper of Komori and Ueda1raises questions of both a theoretical and experimental nature.

ISSN:0031-9171    

DOI:10.1063/1.865360

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An analysis of recent free‐electron laser experiments in combined wiggler and strong axial magnetic fields shows that near resonance, &OHgr;∥=kwv∥, the proximity of the cyclotron maser instability precludes an unambiguous identification of the radiation mechanism (&OHgr;∥is the cyclotron frequency in the axial field,kwis the wiggler wavenumber, andv∥the axial electron velocity).

ISSN:0031-9171    

DOI:10.1063/1.865361

出版商:AIP    

年代:1985

数据来源: AIP