摘要:

The effects of collisions and anisotropy in the ion temperature gradient on the ion‐temperature‐gradient‐driven (ITG) mode are investigated with dissipative trapped electrons and fully kinetic ions, in the presence of both transit and magnetic drift resonances. For the slab and toroidal modes, electron collisions stabilize the ion branch but destabilize the electron branch. For the mixed slab and toroidal mode, a coupling effect is found that causes a split of the stability region in the &eegr;i∥‐&eegr;i⊥plane. A second stability region at large &eegr;i⊥with electron collisions may provide a possible stabilization scheme for ITG instabilities.

ISSN:0899-8221    

DOI:10.1063/1.860669

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The ionic Fokker–Planck code which was written for describing plasma shock wave fronts [M. Casanovaetal. Phys. Rev. Lett.67, 2143 (1991)] is applied to model the collision of two plasmas in plane geometry. Improvements brought to the code for that purpose are described. The initial phase of the experiment during which the plasmas interpenetrate is accounted for by a simple fluid model, which yields qualitative insight into the phenomena at play as well as an initial condition to start the kinetic simulation. The kinetic results obtained in the stagnation and thermalization phases are discussed with respect to a specific laser‐produced plasma collision experiment, as well as to existing fluid and kinetic (‘‘particle‐in‐cell’’) simulations.

ISSN:0899-8221    

DOI:10.1063/1.860670

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The penetration of a magnetic field into a cylindrical plasma of a density that varies both radially and axially is studied. The magnetic field penetrates rapidly due to the Hall field, along constantnr2lines (nis the dimensionless plasma density andris the dimensionless radial coordinate). For a plasma that conducts between two cylindrical electrodes, it is shown that there is magnetic field penetration for both positive and negative polarity cases as long as there is penetration along the electrodes. The magnetic field evolution is found, analytically and numerically, for different time behaviors of the magnetic field at the boundaries. Ion velocities are also calculated.

ISSN:0899-8221    

DOI:10.1063/1.860671

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Drift wave vortices in a cylindrical plasma is studied based on the modulated point vortex model for the Hasegawa–Mima equation. Various types of interactions are revealed such as exchange scattering, trapping, and detrapping, which sometimes bring about a long‐distance radial excursion, resulting in an enhancement of transport.

ISSN:0899-8221    

DOI:10.1063/1.860672

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A class of two‐dimensional force‐free equilibria are shown to be subject to an ideal linear instability. This instability is similar to the coalescence instability for chains of magnetic islands. Semianalytic methods are used to find second magnetic equilibrium which is accessible from the first and has lower magnetic energy. This equilibrium has a discontinuous magnetic field and current sheets at these discontinuities. Numerical simulations indicate that the nonlinear evolution of the instability allows the plasma to relax to this discontinuous equilibrium.

ISSN:0899-8221    

DOI:10.1063/1.860673

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Two‐dimensional tearinglike behavior is studied in reduced resistive magnetohydrodynamics (MHD) with flux conserving boundary conditions on a rectangular box. The tearinglike perturbations do not destroy the symmetries of the initial state, either discrete or continuous. In such cases, in which the perturbation does not break a symmetry of the equilibrium, linear instability is typically not directly observed. However, there can be a loss of equilibrium associated with the existence of a tearing unstable state. These ideas are illustrated with three examples: a very elongated tokamak, a tokamak with pinching coils to elongate its flux surfaces, and a model for the magnetotail or for solar arcades. The loss of equilibrium is demonstrated by means of a nonlinear energy functional. The importance of the fact that the dynamics shows a loss of equilibrium is that a large amount of free energy can be released, in the form of reconnection, and that there is a possibility of hysteresis.

ISSN:0899-8221    

DOI:10.1063/1.860674

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The small amplitude magnetohydrodynamic Riemann problem is studied using the Cohen–Kulsrud–Burgers equations. Unlike the coplanar Riemann problem, the evolution of noncoplanar Riemann problems is not self‐similar and its flow structures could change in time. But its large‐time behavior is very simple and a time‐dependent 2→3 intermediate shock is always involved for the noncoplanar field rotations. The time‐dependent 2→3 intermediate shock has a well‐defined structure and exists for any degree of field rotation.

ISSN:0899-8221    

DOI:10.1063/1.860675

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A traditional cold‐plasma boundary model is revised to allow for proper description of nonlinear effects in surface wave propagation. It is shown that induced nonlinear surface currents can exist at the boundary. As an example, the third‐order ponderomotive phenomena are considered, and the effect of the boundary condition on these nonlinear interactions is examined.  

ISSN:0899-8221    

DOI:10.1063/1.860676

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Motion of charged particles in electrostatic plasma turbulence is studied analytically and numerically. Analytical study is based on a stochastic differential equation, the generalized Langevin equation, which is derived by the projection operator method with the assumption that the random fluctuation field is a Gaussian and wide sense stationary process. The equation describes the particle velocity as a stochastic process driven by field fluctuations, and is applied to evaluate the velocity diffusion coefficient. The non‐Markovian velocity diffusivity is characterized by the retarded turbulent collision term which contributes to the memory effect of the wave–particle interaction. Test‐particle numerical experiments are carried out by following trajectories of charged particles in Langmuir turbulence. The observed diffusion coefficient in a relatively strong turbulence deviates from predicted values of the quasilinear and the extended resonance broadening theories. The present non‐Markovian formulation explains well such a departure of the diffusion rate.

ISSN:0899-8221    

DOI:10.1063/1.860677

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A two‐dimensional magnetohydrodynamic code that includes resistivity and viscosity has been used to study the growth ofm=0 perturbations of a Z pinch in which the current increases with time. Stability for all wave numbers was found when the productSRwas less than about 1000, whereSis the Lundquist number andRis the Alfve´n–Reynolds number. SinceSRdepends only on the line densityN, the stability criterion translates asN<2×1016ions cm−1(deuterium). This is two to three orders of magnitude smaller than the line density of fiber pinch experiments that have shown anomalous stability, and it is concluded that viscoresistive effects are inadequate to account for these observations.

ISSN:0899-8221    

DOI:10.1063/1.860678

出版商:AIP    

年代:1993

数据来源: AIP