摘要:

Motivated by the possibility of collective acceleration of ions trapped in an accelerating space‐charge wave on a strongly magnetized electron beam, the ion trajectories in such a configuration are studied. The motions perpendicular and parallel to the beam direction are coupled by a nonlinear term in the ion Hamiltonian that is proportional to the wave amplitude. Because of this coupling, the motion deviates markedly from that of a linear harmonic oscillator in certain resonant regions of phase space. A sequence of canonical transformations is used to study the motion in these regions. It is shown that wave amplitudes that are too small to trap beam electrons are too small to cause these reasonances to overlap. In the absence of such overlap, the motion is not discernibly ergodic in any three‐dimensional subspace of the energy hypersurface bcause there exists a third constant of the motion in addition to the total energy and angular momentum. These conclusions are verified using surface‐of‐section techniques to study numerically integrated ion trajectories. It is observed that the third constant of the motion constrains on ion initially trapped in a potential well of the wave to remain trapped in the well. Therefore, within the bounds of the physical model presented here, ergodic behavior poses no threat to attempts at collective ion acceleration in space‐charge waves on a electron beam.

ISSN:0031-9171    

DOI:10.1063/1.864338

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In the context of magnetospheric and laboratory beam‐plasma dynamics, there appears to be a need to examine consistently electron beam density development when coupled to a passive resistive background medium. The problem motivating the present study of an electron beam passing through the ionosphere is one case in point; the localized density evacuations predicted may be the forerunner of a low‐frequency, diffusion‐dominated, excitatory mechanism in auroral activity. The contribution offered by this work lies in the technique used to follow the electron beam in space time within a Lagrangian framework via the method of characteristics, consistently feeding back the effect of the field coupling with the resistive medium. This consistency along with a simulation of the influence of a local periodic disturbance are achieved by adjusting the upstream conditions in the characteristics solution. Prediction concerning the nature of the instability from the dispersive equation are shown to agree with those predicted from this generalized technique.

ISSN:0031-9171    

DOI:10.1063/1.864339

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A linear eigenfunction analysis of the beam–plasma instability for an annular beam interacting with a plasma filling the space between the conductors of a coaxial transmission line is presented. The beam and plasma electrons are modeled by relativistic cold fluids and the dispersion relation is three‐dimensional and fully electromagnetic. Particular attention is given to the radial eigenfunction structure and extensive numerical examples are presented. The behavior of the dispersion relation with various parameters is interpreted in terms of the infinite homogeneous theory. Simple analytic approximations for the dispersion relation for annular beams are given. Also, particle‐in‐cell simulation results are compared with the predictions of the linear analysis.

ISSN:0031-9171    

DOI:10.1063/1.864340

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The small‐signal theory of a harmonic gyrotron is presented for the case of axis‐encircling electron orbits. The beam current required for oscillation is found to be highly dependent on the electron energy. Gyrotron cavities operating on this principle at very high harmonic numbers (n&bartil;10) and high frequency in weak magnetic fields are well matched to low‐current, moderate‐energy, rf‐accelerated electron beams (&bartil;50 mA, &bartil;250 keV), resulting in compact submillimeter wave systems.

ISSN:0031-9171    

DOI:10.1063/1.864341

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An electron‐free plasma consisting of negative ions (SF6−) and positive ions (Ar+), and negligible neutral‐ion collision frequencies has been created in the laboratory. This plasma has a mass ratio of approximately 3.5‐similar to many computer particle‐in‐cell simulated systems. A fluid description of this positive and negative ion confinement (PANIC) plasma is given and compared to experimental measurements of a beam–plasma instability for both beam species and a wide range of beam energies. The fluid dispersion relation and most growing modes are predicted to be insensitive to many parameters of the PANIC beam–plasma system, and found to the consistent with the data.

ISSN:0031-9171    

DOI:10.1063/1.864342

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Using a novel directional velocity analyzer the electron distribution function f(v,r,t) is measured in a magnetic‐field‐line reconnection experiment. Runaway electrons are observed inside the current sheet, a result important for transport processes and instabilities.

ISSN:0031-9171    

DOI:10.1063/1.864343

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Time‐ and energy‐resolvedd‐3He fusion reactions have been measured to infer the energy of thed+or He++minority ions heated near their cyclotron frequency by the magnetosonic fast wave. The average energy of the reacting3He ions during3He minority heating is in the range of 100–400 keV, as deduced from the magnitude of the reaction rate, its decay time, and the energy spread of the proton reaction products. The observed reaction rate and its scaling with wave power and electron density and temperature are in qualitative agreement with a radial reaction rate model using the minority distribution predicted from quasilinear velocity space diffusion. Oscillations in the reaction rate are observed concurrent with sawtooth andm=2 magnetohydrodynamic activity in the plasma.

ISSN:0031-9171    

DOI:10.1063/1.864344

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The results of a series of experimental measurements of compact toroidal (CT) plasmas produced by a magnetized coaxial plasma gun injecting into a flux‐conserving metallic liner are reported. The experiments were performed on the Beta II facility at Lawrence Livermore National Laboratory. The magnetic equilibria are well described by a force‐free eigenmode structure that results from an extension of Taylor’s theory of the reversed‐field pinch. Consideration of helicity conservation during relaxation of the composite plasma‐gun flux‐conserver system to the final state equilibrium yields theoretical expressions that are compared with the experiment. In particular the CT poloidal flux (&psgr;pol) and the overall electrical efficiency for producing the CT are predicted to be functions of the plasma gun inner‐electrode flux (&psgr;gun) and the volt‐seconds input to the gun discharge (∫∞0 V dt). Away from a cutoff at too low values of ∫∞0 V dtor too high values, &psgr;gun,&psgr;polscales linearly with the square root of the product of &psgr;gunand ∫∞0V dt, whereas the electrical efficiency equals about 13% for ∫∞0V dt/&psgr;gun≊10. For an electrical energy inputWin=45 kJ, CT’s are produced with poloidal plus toroidal field energy up toWB=8 kJ and toroidal plasma currentItor=330 kA. The chord‐averaged plasma density is 2–4×1014cm−3, and the plasma volume equals 150 liters. The radius of the flux conserver is 37.5 cm, and the axial length is 40 cm. If a bias flux &psgr;bis superimposed on the flux conserver,n=1 tilting is observed when &psgr;b/&psgr;polexceeds a ratio of about 0.20 to 0.25. Impurity radiation measured by a pyroelectric detector accounts for all of the plasma magnetic energy if uniform volume emission of radiation is assumed. The dominant impurities observed are carbon and oxygen. Helium‐like lines are not observed, indicating that the plasma has not ‘‘burned through’’ the low electron temperature radiation maxima. The experimentally observed decay times (defined by thee‐folding time of plasma magnetic fields) are 80 to 160 &mgr;sec—consistent withZeff=2 andTein the range 5–10 eV if classical resistivity is assumed. A zero‐dimensional rate equation model of impurity radiation loss gives a reasonably good account of the experimental observations and predicts that the carbon concentration must be reduced to the level of a few percent to allow burnthrough of the low‐Tecarbon radiation barrier. Glow discharge cleaning of the gun electrodes and flux conserver resulted in a 20% increase of thee‐folding time of plasma magnetic fields (from an average value 115 to 140 &mgr;sec). The CT plasma density was observed to scale linearly with the electrical energy input to the gun discharge and to be only weakly dependent on the filling pressure and timing of pulsed deuterium gas valves. It seems likely that further improvements in increasing plasma lifetime can be made by improving the vacuum conditions and discharge cleaning methods and experimenting with the gun electrode materials.

ISSN:0031-9171    

DOI:10.1063/1.864345

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Using the measured plasma densities and energies, the flow of power between the different particle species and regions of the tandem mirror experiment (TMX) is analyzed. The power flow is described by a simple classical model modified to include: (1) a halo of cool plasma that reduces end‐cell ion losses due to charge exchange on background gas, (2) instability heating of the central‐cell ions both in the central cell and as they escape through the plugs, (3) electron energy transport along the field lines which is less than predicted, and (4) radial transport of the central‐cell ions. Our global power balance, including all particles and regions, accounts for 87±27% of the trapped neutral‐beam power.

ISSN:0031-9171    

DOI:10.1063/1.864346

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The power balance in the Tandem Mirror Experiment (TMX) is studied for several days of operation. Between them, these days typified the operating range of TMX. Examining the power balance on axis, it is found that 60% to 100% of the power is carried to the end walls by escaping central‐cell ions. Globally, these calculations account for 70% to 100% of the input power on each of the days studied. Based upon the power balance, the energy confinement times of the particle species are calculated. The end‐cell ion energy confinement time is similar to that achieved in the 2XIIB single‐cell magnetic mirror experiment, whereas the electron energy confinement in TMX was 10 to 100 times better. The central‐cell ion energy confinement in the central flux tube was determined by axial particle loss. At the central‐cell plasma‐edge radial particle transport and charge exchange with the fueling gas are important processes.

ISSN:0031-9171    

DOI:10.1063/1.864347

出版商:AIP    

年代:1983

数据来源: AIP