摘要:

It is demonstrated that particle‐simulation techniques can explore a broad range of dynamical behavior exhibited by non‐neutral plasmas. New features isolated by this approach include collective relaxation through generation of core and halo populations; self‐organization without radial transport as the plasma is cooled; spontaneous generation of solitonlike structures upon axial reflection from the external confining potential.

ISSN:0899-8221    

DOI:10.1063/1.860712

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

It is demonstrated both analytically and numerically that mode couplings play an important role in the nonlinear evolution of alpha‐particle‐drivenlongwavelengthAlfve´n wave instabilities. The mode coupling process is characterized by a beat between two linearly unstable Alfve´n waves having opposite frequencies, which generates a linearly stable, static (zero frequency) mode. The backreaction of the static mode tends to stabilize the Alfve´n instabilities by eliminating the phase shift between the alpha pressure and the Alfve´n fluctuations.

ISSN:0899-8221    

DOI:10.1063/1.860713

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The nonlocal power absorption of trapped ions in ion cyclotron radio‐frequency heating is calculated for several non‐Maxwellian distribution functions by keeping the full particle orbit and wave coupling. For slowing down distribution the finite Larmor radius effect enhances the power absorption in higher harmonic heating withn≥2. In bi‐Maxwellian plasma the absorption of trapped ions increases with the power of the ratio of the thermal perpendicular energy to the thermal parallel energy in the infinite aspect ratio limit and is slower in the small inverse aspect ratio case.

ISSN:0899-8221    

DOI:10.1063/1.860714

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Relativistic test particles interacting with a small monochromatic electromagnetic wave are studied in the presence of an inhomogeneous background magnetic field. A resonance‐averaged Hamiltonian is derived which retains the effects of passage through resonance. Two distinct regimes are found. In the strongly inhomogeneous case, the resonant phase angle at successive resonances is random, and multiple resonant interactions lead to a random walk in phase space. In the other, adiabatic limit, the phase angle is determined by the phase portrait of the Hamiltonian and leads to a systematic change in the appropriate canonical action (and therefore in the energy and pitch angle), so that the cumulative effect increases directly with the number of resonances.

ISSN:0899-8221    

DOI:10.1063/1.860715

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The recently developed perturbation theory of transit‐time interactions between particles and coherent wave packets in magnetized plasmas is applied to particular field structures. Limits of validity are determined by comparison with test‐particle simulations, showing that the theory is accurate everywhere except near certain well‐determined resonances, for wave fields exceeding a characteristic threshold, and for particles below a particular velocity. The properties of transit‐time interactions in magnetized plasmas are investigated in detail to determine their dependence on the fields and parameters of the particle motion. Resonant particle scattering is found to occur at low particle velocities when the frequency of the coherent wave packet is an integer multiple of the gyrofrequency. Two different types of resonant transit‐time dissipation are also observed: one arises from transient cyclotron acceleration in the localized wave packet, the other from beating between the gyration of the particles and the oscillation of the wave packet field. Both effects involve an interplay between the field geometry and resonant oscillations.

ISSN:0899-8221    

DOI:10.1063/1.860716

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The electrostatic potential is determined for a test electron withv∥≫vTein a uniform magnetized plasma (&ohgr;ce≫ &ohgr;pe). In the frame of the test electron, part of the spatially oscillatory potential has spherical symmetry over the hemisphere to the rear of the electron and is zero ahead of the electron. A second part of different character, which makes the potential continuous at the plane containing the electron, is oscillatory in the radial direction but decreases almost monotonically in the axial direction.

ISSN:0899-8221    

DOI:10.1063/1.860717

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

For slab geometry the perturbation of the electrostatic wake of a superthermal test electron in a magnetized plasma (&ohgr;ce≫ &ohgr;pe) due to moderate magnetic shear is determined. Allowing for the spherical symmetry of the surfaces of constant phase to the rear of the test electron, the ‘‘resonant’’ field electrons causing the damping of the wave in a magnetic surface at a distancexfrom the test electron are those with parallel velocityv’∥=v∥cos&bgr;/cos(&bgr; + &ggr;). Here &bgr; is the angle between the emitted ray andB(0), &ggr; is the angle betweenB(0) andB(x) andv∥is the velocity of the test electron. As a result the damping in the WKB approximation for the wave emission is a function of both the angle of emission and &ggr;. A Fokker–Planck equation is derived for the rate of change of the electron distribution function (f) due to the emission and absorption of the waves under these conditions;fis assumed approximately Maxwellian forv∥≲vTbut with an arbitrary tail forv∥≳vT.

ISSN:0899-8221    

DOI:10.1063/1.860665

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A linear analysis of ion Bernstein wave (IBW) propagation and absorption is considered in a general tokamak plasma magnetic equilibrium. The effects of elongation, triangularity, and Shafranov shift on radio‐frequency (rf) absorption are discussed with respect to the simple case of circular and concentric magnetic surfaces. The ray‐tracing equations are analytically and numerically solved in the flux surface coordinate system, and the power deposited in the plasma is calculated along the trajectory for the International Thermonuclear Experimental Reactor (ITER) [Nucl. Fusion31, 1135 (1991)] plasma parameters.  

ISSN:0899-8221    

DOI:10.1063/1.860666

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The long‐time behavior of charged particles in plasma turbulence with uniform broad wave spectrum is studied numerically. The diffusivity of the particle velocity distribution is characterized by the quasilinear nature for extended time, while a transient diffusion precedes with the enhanced nonquasilinear diffusion rate when resonance overlapping is relatively weak. The observed long‐time quasilinear diffusion coefficient eventually decreases due to the finiteness of the resonance region. The transient‐type diffusion is revealed only by the higher‐order numerical calculation.

ISSN:0899-8221    

DOI:10.1063/1.860667

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Numerical simulations on the thermal convection of a neutral fluid (without a magnetic field) in a rotating spherical shell have been carried out. The results indicate that sufficiently rapid rotation results in strong differential rotation, with a pronounced equatorial acceleration. The formation dynamics of convection columns aligned to the rotation axis is studied extensively. A new generation mechanism of differential rotation is then proposed which concludes that the fluid motion generates an equatorial acceleration by selectively exciting the cyclonic columns in the spherical shell.

ISSN:0899-8221    

DOI:10.1063/1.860668

出版商:AIP    

年代:1993

数据来源: AIP