摘要:

The dispersal of a localized density fluctuation in a uniform magnetoplasma is studied using the macroscopic fluid equations. Expressions are obtained for the Fourier‐Laplace transforms of the perturbed density, potential field, and flux distributions. These expressions are inverse transformed, using a combination of analytic and numeric techniques. The resulting curves which display the real space and time development of the system are then compared with magnetic‐field‐free ambipolar diffusion. One finds that diffusion along the magnetic field,&thgr; = 0°, is much more rapid than ambipolar diffusion, that when the ion motion is not affected by the magnetic field, diffusion at&thgr; = 90°proceeds at approximately the ambipolar rate, and that the electron and ion fluxes are not ambipolar.

ISSN:0031-9171    

DOI:10.1063/1.1693672

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The effects of noise (caused by collisions or weak turbulence) on the production of echoes in magnetically trapped particles is discussed using a propagator formalism. Provided the effective collision time is long compared with a typical bounce time, the echoes are found to be broadened but not destroyed.

ISSN:0031-9171    

DOI:10.1063/1.1693673

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The departure of the radiation temperatureTrfrom the kinetic temperature of the emitting electrons can be used as a measure of the distribution of electron velocitiesf(v). This relationship betweenTrandf(v), using the theory of fluctuations of random currents is explored theoretically. The method is particularly suited to radiation from relatively small, bounded plasmas of laboratory size where the traditional theory of radiative transport of wave packets becomes questionable.

ISSN:0031-9171    

DOI:10.1063/1.1693674

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Time‐resolved measurements of the radiation temperatureTrin a weakly ionized plasma column subjected to an axial magnetic field are reported. The experiments are made at frequencies near the electron cyclotron frequency during and in the early afterglow of a pulsed argon discharge. The observed departures ofTrfrom the kinetic temperature are used in the determination of the distribution of electron velocitiesf(v). A comparison of the steady‐state distribution with computations based on an appropriate kinetic model shows good agreement and establishes the validity of this experimental method of measuringf(v). In addition, the measured time dependence off(v)allows the inference of the rates of electron‐atom cooling and electron‐electron relaxation, during the early afterglow of the pulsed discharge.

ISSN:0031-9171    

DOI:10.1063/1.1693675

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Numerical solutions of the Vlasov and Poisson equations for several physically significant problems are presented and compared with the results of particle simulations. The numerical solutions of the Vlasov equation are based on the Fourier‐Fourier transform method. The spatial representation includes up to 85 modes and is capable of representing strong nonlinear effects. The particle simulations are based on a multipole expansion of finite‐size particles about their nearest grid point location. Special techniques are used to suppress the noise and to accurately control the initial conditions of the plasmas so that quantitative comparisons with Vlasov solutions can be made. Close quantitative agreement between the results of the two simulation techniques is observed. The problems considered are one‐dimensional, with periodic boundary conditions, and involve (1) two‐stream instabilities, with equal and unequal electron beams, and (2) large‐amplitude electron oscillations, with sideband instabilities.

ISSN:0031-9171    

DOI:10.1063/1.1693676

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The time evolution of an ion distribution function is computed in the sheath about a negatively pulsed transparent grid. The algorithm details the ion flow in the potential well when the pulse is on and the burst of ions ejected after the pulse potential is removed.

ISSN:0031-9171    

DOI:10.1063/1.1693677

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Microwave frequencies of 0.4‐24 GHz at powers up to 100 kW have been used to heat electrons in regions of cyclotron resonance in a supported and in a levitated toroidal octupole magnetic field. A theoretical model has been developed to predict the heating rate of a cold, tenuous plasma in an arbitrary, nonuniform, magnetic field. The model predicts strong heating at places where∇‖B = 0at resonance, and heating efficiencies approaching 100% for sufficiently high densities(&ohgr;p2>&ohgr;2/Q). Scintillator probes have been used to verify the predicted localized heating and to measure the density at which total absorption occurs. Gun injected plasmas and microwave produced plasmas withn∼109 cm−3andkTe∼5 eVare heated to≲ 1 KeVin the supported octupole and to≲ 10 KeVin the levitated octupole. Upper off‐resonance heating is also observed.

ISSN:0031-9171    

DOI:10.1063/1.1693678

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Inertial subrange expressions for the structure functions of a turbulent passive scalar field are derived taking into account the fluctuations in dissipation rates of scalar and velocity fields.

ISSN:0031-9171    

DOI:10.1063/1.1693679

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Asymptotic decay rates for mean concentration and root‐mean‐square fluctuations in concentration are derived for a decaying second‐order, isothermal two‐species reaction in final period turbulence.

ISSN:0031-9171    

DOI:10.1063/1.1693680

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A solution for the time evolution of the velocity correlation function in homogeneous isotropic turbulence is obtained using multipoint distribution functions. The dependence of the velocity correlation function on the fluid parameters is calculated for a simple initial condition.

ISSN:0031-9171    

DOI:10.1063/1.1693681

出版商:AIP    

年代:1971

数据来源: AIP