摘要:

The interaction of ions with electromagnetic waves at frequencies on the order of the ion cyclotron frequency is studied without the assumption of geometrical optics. Instead, it is assumed that the time for an ion to travel one wavelength is large compared with the wave period. Such a scaling admits nontrivial effects of the plasma geometry and is particularly appropriate to the ELMO Bumpy Torus experiment. The relevant frequency range is from one to a moderate multiple of the ion cyclotron frequency. It is shown that the ion response may be represented by the usual cold ion conductivity and with appropriate jump conditions across the fundamental resonant surface. Nonresonant energy transfer is calculated and shown to exist under many circumstances, depending on the antenna and electron response. Expressions are given for the resonant energy absorption at the fundamental and second harmonic. At higher harmonics, the nonresonant energy transfer is large compared with the resonant absorption.

ISSN:0031-9171    

DOI:10.1063/1.864252

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A theory of particle motion in stellarators is developed which, in contrast to previous work, is both realistic enough to account for collisionless detrapping, yet simple enough that most features of the orbits can be expressed in analytic, reasonably simple formulas. From the study of detrapping, a systematic, complete classification of possible orbit types emerges. The theory is valid for a class of stellarator configurations which contains the standard model traditionally envisaged, as well as somewhat more complex configurations recently found to have favorable transport properties. The reasons for the differences in transport between configurations are elucidated.

ISSN:0031-9171    

DOI:10.1063/1.864232

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The diffusion model for multiple mirror confinement has previously been limited to devices with a large number of cells and high mirror ratios. Ambipolar effects were assumed to reduce the confinement time by the usual factor [1+Z(Te/Ti)]−1. For the ideal multiple mirror regime, in which the mean free path is shorter than the cell length but long compared with the mirror scale length, a new discrete staircase density profile model, without those limitations, has been developed. A theory employing model distribution functions for ion and electron transport in a multiple mirror device has been used. A self‐consistent ambipolar potential is included. It has been found that the ambipolar potential reduces the confinement time somewhat less than the usual ambipolar factor. Special attention is given to the last cell which acts as a boundary condition for the system. The ambipolar potential across the last mirror throat is studied and found to be of the order of 0.3kTe. For devices with small numbers of cells, significant improvements over previously calculated multiple mirror confinement times are found.

ISSN:0031-9171    

DOI:10.1063/1.864233

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The condition for having strictly omnigenous magnetic fields (zero geodesic curvature and neoclassical step size) is generalized to determine the fields which give the smallest mean square neoclassical step size consistent with given boundary conditions and constraints. Because this transport minimization produces less restrictive field configurations than omnigenity, a wider class of practical applications is possible. An explicit set of ordinary differential equations is obtained for the transport‐minimizing vacuum fields in long‐thin tandem mirror geometry. Configurations with reduced transport are found at little cost in line averaged interchange stability. Additionally, for these configurations the constraint that no parallel current flow into the center cell (due to the Stupakov effect) may be imposed in a natural way.

ISSN:0031-9171    

DOI:10.1063/1.864234

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The bounce averaged Fokker–Planck equation is solved for alpha particles slowing down in a background plasma of elecrons and ions in the central cell of a tandem mirror. The problem is formulated for a general, monotonic magnetic field, and then solved numerically for the square‐well case. This gives a distribution function in energy and lambda (magnetic moment/energy). The resulting loss of alpha particles by scattering into the magnetic loss cone and the distribution of alpha‐particle energy to ions and electrons are given. For typical tandem mirror reactor parameters (Te∼30 keV, &fgr;∼100 keV,R∼4) about half of the alpha particles are born in or scatter into the loss cones, but less than 25% of the total alpha particles’ energy is lost through these mechanisms.

ISSN:0031-9171    

DOI:10.1063/1.864235

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A new, steady‐state linear machine has been constructed which produces a low‐density, low‐temperature hydrogen plasma in the collisionality regime of the dissipative trapped ion instability. This instability was seen and identified through the observed dependence of the wave amplitude on trapped fraction, axial and radial position, and collisionality and through the scaling of the real frequency with trapped fraction. The observed radial and axial mode structure of the instability is compared with the results of a simple radial model and a calculation of the Landau damping for both trapped and transit particles in a linear geometry.

ISSN:0031-9171    

DOI:10.1063/1.864236

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The mechanism of plasma acceleration by a traveling wave is derived from a cold plasma magnetohydrodynamic model with finite conductivity and finite Hall parameter. It is shown that collective effects may strongly influence the dynamics of the acceleration process. Eigenmodes of the plasma column considerably improve the acceleration whereas in general, plasma turbulence, induced by the primary wave, will reduce the efficiency of the process. Both mechanisms are demonstrated in an experiment where a high‐amplitude traveling‐wave pulse accelerates a nearly fully ionized plasma. In this experiment the flow profile is determined by the balance of electromagnetic and viscous forces. This enables one to determine the viscosity spectroscopically by measuring the flow velocity of the plasma. The experimental value of the viscosity is in accordance with the Spitzer formula.

ISSN:0031-9171    

DOI:10.1063/1.864237

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The behavior of the implosion and post‐implosion phases of two different toroidal high‐beta plasma configurations has been investigated. The plasma is produced in a nominally axisymmetric toroidal theta pinch in which a tokamak‐like low‐beta plasma is heated and compressed to high beta by a fast‐rising toroidal field. The two plasma cases differed from each other by the direction of their initial toroidal magnetic field relative to the direction of the main implosion magnetic field. The purpose of this investigation was to determine what factors govern the development and lifetime of the magnetic configuration during the early time post‐implosion phase. It was determined from theqprofiles for the parallel field case that the plasma should be unstable to them=1 kink mode, i.e.,q<1, but the normal outward shift of the plasma with respect to the external conducting wall carried it into the internal vacuum chamber wall before the kink could grow to an observable level. The magnetic fields in the case with the initial toroidal field antiparallel to the main implosion magnetic field exhibited nonaxisymmetric behavior.

ISSN:0031-9171    

DOI:10.1063/1.864218

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Threshold conditions are analyzed for stimulated Raman backscattering (SRS) from an underdense plasma in the presence of ion‐acoustic fluctuations. For typical ion‐acoustic spectra which could result from a Brillouin instability occurring simultaneously with SRS, a reduced collisional threshold due to induced bremsstrahlung is found for the Raman instability. Similarly, for inhomogeneous plasma the phase mismatch created by a density gradient can be compensated for by an inhomogeneity in the ion‐acoustic spectrum; as a consequence, the inhomogeneity threshold for absolute instability can be substantially reduced. Comparisons are made with experimental observations of stimulated Raman scattering in the presence of strong stimulated Brillouin scattering for CO2laser‐plasma interaction. It is found theoretically that for fluctuation levels typical of that accompanying SBS, induced bremsstrahlung growth rates for Langmuir waves can be of the order of collisional damping rates.

ISSN:0031-9171    

DOI:10.1063/1.864219

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Stimulated Brillouin scattering in a plasma containing broad‐bandwidth thermal noise was considered. Plasma profiles which are inhomogeneous (for example, because of a velocity gradient) were studied. At each point in the profile, a different electromagnetic wave can be resonant with the pump wave and a local ion acoustic wave, and can thus be amplified from its noise level. Some difficult points of the linear theory of this process are first examined. Then a nonlinear equation is derived, which governs the decrease of the incident‐wave amplitude as it propagates toward the critical density surface. Solutions of this equation predict a maximum value of the absorbed intensity,Imax. For incident laser intensitiesIin, higher than this value, only a fractionImax/Iinis absorbed.

ISSN:0031-9171    

DOI:10.1063/1.864220

出版商:AIP    

年代:1983

数据来源: AIP