ISSN:0899-8221    

DOI:10.1063/1.3480477

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A full‐wave equation has been obtained from the gyrokinetic theory for the fast wave traversing a minority cyclotron resonance [Phys. Fluids B4, 493 (1992)] with the aid of the fast wave approximation [Phys. Fluids31, 1614 (1988)]. This theory describes the transmission, reflection, and absorption of the fast wave for arbitrary values of the parallel wave number. For oblique propagation the absorption is due to both ion cyclotron damping by minority ions and mode conversion to the ion Bernstein wave. The results for a3He minority in a D plasma indicate that for perpendicular propagation and minority temperatures of a few keV the power lost by the fast wave is all mode converted whereas for minority temperatures ∼100 keV∼30% of the incident power is dissipated by the minority ions due to the gyrokinetic correction. The gyrokinetic correction also results in a significant reduction in the reflection coefficient for low field side incidence whenkzLB≲1 and the minority and hybrid resonances overlap.  

ISSN:0899-8221    

DOI:10.1063/1.860865

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In the homogeneous Hasegawa–Mima equation, the dipole vortex or modon solution is well known to be robustly stable from both analytic and numerical studies. In the inhomogeneous plasma where∇Te≠0 the corresponding vortex has an external structure extending into the high‐temperature region. Lyapunov stability method is used to determine the stability properties of these extended vortex structures. The overall growth rate of deformation caused by the presence of temperature inhomogeneity is shown to be bounded by (R/LT)2, whereRis the radius of the core of the vortex andLTis the scale length of the temperature gradient. The most important source of instability is identified as the excitation of monopolar and dipolar perturbations with short spatial scales ≲R, which are approximately independent of the presence of the density and temperature gradients.

ISSN:0899-8221    

DOI:10.1063/1.860872

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Nonaxisymmetric (∂/∂&thgr;≠0) rotating equilibria are investigated theoretically for strongly magnetized, low‐density (&ohgr;pe2/&ohgr;ce2≪1) pure electron plasmas confined in cylindrical geometry. These two‐dimensional equilibria are also called rotating coherent structures, and are stationary (time independent) in a frame of reference rotating with angular velocity &ohgr;r=const about the cylinder axis (r=0). Radial confinement of the pure electron plasma is provided by a uniform axial magnetic fieldB0ez, and a grounded, perfectly conducting, cylindrical wall is located at radiusr=rw. The analysis is based on a nonrelativistic, guiding‐center model in the cold‐fluid limit (the continuity and Poisson equations) that treats the electrons as a massless fluid (me→0) withE×Bflow velocityVe=−(c/B0)∇&fgr;×ez. Within this model, general rotating equilibria with electron densityne≡nR(r,&thgr;−&ohgr;rt) and electrostatic potential &fgr;≡&fgr;R(r,&thgr;−&ohgr;rt) have the property that the electron density is functionally related to the streamfunction &psgr;R=−e&fgr;R+&ohgr;r(eB0/2c)r2bynR=nR(&psgr;R).The streamfunction &psgr;Rsatisfies the nonlinear equilibrium equation ∇2&psgr;R=−4&pgr;e2nR(&psgr;R)+2&ohgr;reB0/cwith &psgr;R=&ohgr;r(eB0/2c)rw2≡&psgr;w=const on the cylindrical wall atr=rw. Following a general discussion of rotating equilibria, an integral equation formulation of the nonlinear equilibrium equation is developed to investigate equilibria with ‘‘waterbag’’ (step‐function) density profiles. In this investigation, a numerical method is formulated that can be used to construct diverse classes of highly nonlinear waterbag equilibria. This method is employed to investigate two classes of nonaxisymmetric equilibria that are nonlinear extrapolations of well‐known small‐amplitude equilibria. These two classes of rotating equilibria bear strong similarities to coherent structures observed experimentally by Driscoll and Fine [Phys. Fluids B2, 1359 (1990)].

ISSN:0899-8221    

DOI:10.1063/1.860853

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The evolution of strongly modulated wave packets in a dispersive plasma that propagate parallel to the magnetic field is studied. Modulation effects are shown to reduce significantly (≊30%) the rate of spreading from that due to dispersion alone. For fluidlike behavior, nonlinearity has its greatest impact on evolution when the linear sound speed and initial wave packet speeds are well matched, resulting in a strong coupling between the wave magnetic and sonic components. Ion kinetic processes reduce the impact of nonlinearity and cause the rate of spreading to approach that expected from dispersion alone as the ratio of ion and electron temperatures,Ti/Te→4. For &bgr;≳1 andTi/Te∼1, the coupled waveforms correspond qualitatively to kinetic treatments of the derivative nonlinear Schro¨dinger (DNLS) equation.

ISSN:0899-8221    

DOI:10.1063/1.860866

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Employing the Zubarev method for the derivation of a nonequilibrium statistical operator, Vlasov–Uehling–Uhlenbeck quantum kinetic equations are derived for the distribution functions of clusters with arbitrary mass number. Considering a partially ionized hydrogen plasma, the electronic distribution function is determined numerically for the homogeneous and stationary case. Restricting to elastic scattering processes between the electrons, ions and atoms, the analytical solution of Schenter and Liboff [Phys. Fluids30, 1789 (1987)] is reproduced. Furthermore, the influence of inelastic collisions such as ionization is investigated. Using the electronic distribution function, the electrical conductivity is calculated for hydrogen plasma of a given composition at arbitrary field strengths. The nonlinear behavior obtained is dependent on the different expressions applied for the electron–atom and the electron–ion cross sections. The effect of inelastic collisions is, in general, a lowering of the conductivity because such processes lead to a limitation of the energy gain of electrons in an electric field.  

ISSN:0899-8221    

DOI:10.1063/1.860867

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The renormalization group (RNG) method is used to study the physics of two‐dimensional (2‐D) magnetohydrodynamic (MHD) turbulence. It is shown that, for a turbulent magnetofluid in two dimensions, no RNG transformation fixed point exists on account of the coexistence of energy transfer to small scales and mean‐square magnetic flux transfer to large scales. The absence of a fixed point renders the RNG method incapable of describing the 2‐D MHD system. A similar conclusion is reached for 2‐D hydrodynamics, where enstrophy flows to small scales and energy to large scales. These analyses suggest that the applicability of the RNG method to turbulent systems is intrinsically limited, especially in the case of systems with dual‐direction transfer.

ISSN:0899-8221    

DOI:10.1063/1.860868

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An improvement of the Albritton nonlocal electron heat transport model is proposed for high‐Zplasmas. The thermal decay of the temperature perturbation in a uniform plasma as calculated by this model is compared with that obtained by Fokker–Planck simulations. Complete agreement is found up to valuesk&lgr;e&bartil;0.1, wherekis the wave number of the perturbation and &lgr;eis the thermal electron mean‐free path.

ISSN:0899-8221    

DOI:10.1063/1.860869

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A new scheme that evolves the perturbed part of the distribution function along a set of characteristics that solves the fully nonlinear gyrokinetic equations is presented. This low‐noise nonlinear characteristic method for particle simulation is an extension of the partially linear weighting scheme, and may be considered an improvement over existing &dgr;fmethods. Some of the features of this new method include the ability to keep all nonlinearities, particularly those associated with the velocity space, the use of conventional particle loading techniques, and also the retention of the conservation properties of the original gyrokinetic system in the numerically converged limit. The new method is used to study a one‐dimensional drift wave model that isolates the parallel velocity nonlinearity. A mode coupling calculation for the saturation amplitude is given, which is in good agreement with the simulation results. Finally, the method is extended to the electromagnetic gyrokinetic equations in general geometry.

ISSN:0899-8221    

DOI:10.1063/1.860870

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

At the onset of the L–H transition in the DIII‐D tokamak [PlasmaPhysicsandControlledNuclearFusionResearch, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p.159], a fast (≊100 &mgr;sec) suppression of microturbulence is observed as the edge transport barrier is formed. This fast edge suppression is followed by a much slower (tens of msec), but substantial (≥50%) reduction in the relative density fluctuation level. This second turbulence suppression phase, which is observed to correlate with growingE×Bvelocity shear, has been localized to the plasmainterior, and may explain why the observed transport reduction in the H mode has been observed to extend deep into the plasma, well beyond the edge transport barrier.

ISSN:0899-8221    

DOI:10.1063/1.860871

出版商:AIP    

年代:1993

数据来源: AIP