摘要:

A Vlasov plasma with a double‐humped, unstable ion velocity distribution function is considered. A&dgr;function in space is assumed as the initial perturbation and the plasma response to this perturbation is calculated, i.e., the Green's function for the problem is found. The response can be divided into two parts: a self‐similar, damped part of the formt−1h(x/t), and an unstable, exponentially growing part. The conditions for absolute and convective growth of the latter are discussed.

ISSN:0031-9171    

DOI:10.1063/1.1694694

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The nonlinear evolution of plane hydromagnetic fluctuations propagating along the unperturbed magnetic field direction is considered. From an expansion of the ideal magnetohydrodynamic equations and the hydromagnetic shock jump conditions, it is shown that a wave in which the magnitude of the magnetic field is nonconstant steepens into a shock and subsequently evolves toward a purely Alfve´nic fluctuations of lower mean energy density. Explicit expressions are derived for the asymptotic state and for the characteristic lines which describe the evolution toward that state. A class of fluctuations which includes linearly polarized waves is shown to evolve into rotational discontinuities. The results are applied to observations of hydromagnetic fluctuations in the solar wind.

ISSN:0031-9171    

DOI:10.1063/1.1694695

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Observations of high current relativistic electron coils are presented and interpreted theoretically. Electron coil self‐magnetic field strengths up to almost twice that of the external magnetic field at the mirror center are observed. Lifetimes up to 30&mgr;secare related to the classical diffusion of electron coils in a stable equilibrium state. The diffusion mechanism is verified as inelastic small angle scattering of the relativistic electrons from a neutral gas background.

ISSN:0031-9171    

DOI:10.1063/1.1694696

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The structure of the plasma boundary, in a tokamak with a poloidal divertor, is considered. The assumption, of hot, collisionless ions, and cold, collisional electrons is shown to be self‐consistent. The density gradient length is shown to be of the order of&rgr;pi, the ion poloidal gyroradius, at typical poloidal angles. Plasma diffusion across the separatrix, and particle motion along the field lines to the collector plates, are described by a kinetic equation. From the solution of the boundary‐layer problem, the ion flux and ion energy flux, to the plates, are calculated. The ratio of these fluxes, and the corresponding ratio for the electrons, complete the specification ofdivertor boundary conditions, to be used in tokamak transport codes.

ISSN:0031-9171    

DOI:10.1063/1.1694697

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The propagation of ion cyclotron waves and fast waves in a toroidal cavity with a spatially varying static magnetic field as in a tokamak or stellarator is examined. Using a cold plasma model in a square cross section conducting toroidal cavity and neglecting effects of electron inertia, the wave equation is reduced to an ordinary differential equation which is numerically integrated subject to boundary conditions to find eigenmodes which represent cavity resonances. For the fast wave, only very small perturbations from the corresponding uniform plasma guide problem are found, and it is concluded that effects of toroidicity on the fast wave are not significant. For the ion cyclotron wave it is found that the region of propagation is generally confined to the high magnetic field side of the cyclotron resonance and for low order modes vertically and azimuthally, the region of propagation does not extend to the resonance location. A new type of wave behavior appears due to toroidicity which is similar to the ion cyclotron wave but depends differently on wavelength and may be important for fusion plasma heating because of its possibly greater accessibility. On the basis of the wave profiles, optimum antenna designs will be profoundly affected by toroidicity.

ISSN:0031-9171    

DOI:10.1063/1.1694698

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Probability distributions for Fourier components of the electric field, including joint distributions for various Fourier components and multiple time distributions for the same component, are determined using the central limit theorem of probability theory and two assumptions within the spirit of weak turbulence theory. The distributions are all Gaussians or simple integrals of Gaussians. This statistical framework is applied to the special case where the turbulence is dominated by the wave‐particle interaction. In this case, quantities appearing in the distributions as parameters, such as the mean and standard deviation, are determined by quasilinear theory and Dupree's recent theory of phase space granulation, or clumps.

ISSN:0031-9171    

DOI:10.1063/1.1694699

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Electrostatic, one‐dimensional, numerical plasma simulations have been used to study results from the University of Saskatchewan turbulent heating experiment. In a simulation plasma with an initial sinusoidal density perturbation (approximating the effect of a bumpy magnetic field parallel to the plasma current in the experiment), the application of a constant external‐electric field can cause the electrons to split into two groups, one freely accelerating and the other trapped near zero velocity in a potential well resulting from the inhomogeneous ion density. The ensuing electron‐electron instability can cause reduced acceleration and heating of the electrons, even when the ions are infinitely massive. This process appears to have a role in the experiment although close quantitative agreement cannot be claimed. A common and important feature of the simulations was the tendency of all observed instabilities to heat the electrons at a rate which maintained the ratio of electron drift to thermal velocity near unity. This heating rate has been observed in the experiment.

ISSN:0031-9171    

DOI:10.1063/1.1694700

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Soft x‐ray emission from the Maryland high voltage&thgr;‐pinch is measured as a function of two experimental parameters which in effect determines the electron density in the initial plasma. The x‐ray intensity increases rapidly as the electron density is lowered; however, the electron temperature deduced from thin foil absorption of these x rays does not vary significantly. The absolute intensity of these about 3‐keV x rays is orders of magnitude larger than the calculated intensity of bremsstrahlung radiation. To enhance x‐ray emission, we put a small Cu target in the plasma, and measure absorption characteristics and intensity of these target x rays also. The time of x‐ray emission correlates with those of neutron emission and implosion of magnetic field on the axis.

ISSN:0031-9171    

DOI:10.1063/1.1694701

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The synchrotron radiation spectrum is calculated for an intense relativistic nonneutralElayer including self‐field effects. The analysis is carried out for the class of thinE‐layer equilibria described self‐consistently by equilibrium distribution functions of the formfe0 (x, p) = R0F(H)&dgr;(P&thgr; − P0), whereHis the energy, is the canonical angular momentum, andR0andp0are constants. Since individual electrons execute radial betatron oscillations about a helix with mean radiusR0, the single‐particle emission spectrum is modified from the conventional Schott‐Trubnikov result. To determine the spectrum of radiation emitted by all electrons in theElayer, the single‐particle emission spectrum is averaged over the distribution functionfe0 (x, p)that self‐consistently generates theElayer equilibrium.

ISSN:0031-9171    

DOI:10.1063/1.1694702

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The one‐dimensional Helmholtz equationw″ + k02g(z)w(z) = ,k0 = 2&pgr;/&lgr;0, is solved making use of an extension of Langer's method. The functiong(z)is restricted to the class of Epstein profiles,g(z) = g(0) + [1 − g(0)] tanh2(z/2&lgr;), where&lgr;is the scale length, corresponding to no turning points, a quadratic turning point atz = 0, or a pair of turning points, depending on whetherg(0)is positive, zero, or negative. This method yields uniformly valid solutions in terms of confluent hypergeometric functions. First, a solutionw+(z)is obtained for0 ≤ zwhich, asz → ∞, becomes the transmitted plane wave. Then, applying the method of analytic continuation, a linear combination is obtainedw−(z) = wi(z) + wr(z)valid forz ≤ 0which, asz → − ∞, yields the superposition of the incident and reflected plane waves. As an illustration of this method and as an application to parabolic density profiles, the mean energy density of the electric field is obtained numerically, in the vicinity ofz = 0, when the parameter ratio&lgr;/&lgr;0 ≥ 100, and for the case of a single quadratic turning point and also for the case in which there are two neighboring turning points. With this choice of parameters, the results yield useful information on the tuning criterion for parametric excitation of the ionosphere.

ISSN:0031-9171    

DOI:10.1063/1.1694703

出版商:AIP    

年代:1974

数据来源: AIP