摘要:

The internal kink mode is destabilized by trapped high‐energy particles, leading to a new branch of the internal kink dispersion relation with a real frequency near the average trapped‐particle precession frequency and a growth rate of the same magnitude. This trapped particle branch of the dispersion relation is investigated numerically for a variety of particle distributions. Mode growth rate and frequency is found as a function of plasma &bgr;, density, and trapped‐particle energy and distribution. The high‐energy trapped particle sources considered are neutral beam injection, ion‐cyclotron heating, and fusion alpha particles. Relevance for various plasma heating schemes is discussed.

ISSN:0031-9171    

DOI:10.1063/1.865198

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The spectrum of stable resistive magnetohydrodynamic modes is shown to be determined by the geometry of anti‐Stokes lines. Behavior of the eigenfunctions is also examined.

ISSN:0031-9171    

DOI:10.1063/1.865199

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Curvature and finite pressure are known to have a dramatic influence on linear magnetic tearing stability. An analytic theory of the nonlinear resistive growth of magnetic islands in tokamaks that includes the interchange driving term in presented here. A Grad‐Shafranov equation to describe the magnetohydrodynamic (MHD) equilibrium of thin islands is derived. The resistive evolution of these islands is then obtained. Interchange effects are found to become progressively less important with increasing island width.

ISSN:0031-9171    

DOI:10.1063/1.865200

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The nonlinear dynamics of the magnetohydrodynamic sheet pinch have been investigated as an unforced initial value problem for large scale Reynolds numbers up to 1000. Reconnection is triggered by adding to the sheet pinch a small but finite level of broadband random perturbations. Effects of turbulence in the solutions include the production of reconnected magnetic islands at rates that are insensitive to resistivity at early times. This is explained by noting that electric field fluctuations near the X point produce irregularities in the vector potential, sometimes taking the form of ‘‘magnetic bubbles,’’ which allow rapid change of field topology.

ISSN:0031-9171    

DOI:10.1063/1.865147

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The properties of steady‐state discharges with stochastic magnetic fields are considered using a fluid model. Magnetic field stochasticity provides a simple explanation of the phenomenon of relaxation of a discharge, defined by J. B. Taylor.

ISSN:0031-9171    

DOI:10.1063/1.865148

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Effects of the metal plasma jet emitted from the cathode spot of a vacuum arc (or a unipolar arc) on the surrounding electric field variation are investigated. It is shown, using a 2‐D magnetogasdynamical model, that the cooling of the expanding metal plasma over the cathode surface leads to a strong variation of the electrical conductivity across the thermal boundary layer. This effect, which was ignored in previous theories of the cathode spot, coupled with the induced electric field caused by the plasma motion across magnetic fields which are caused by the arc current and the external currents, gives rise to a strong electric field at the cathode surface. Solving a mixed‐boundary‐value problem for the electric potential, it is shown that the induced electric field is consistent with the random and the directed retrograde motions of the cathodic arc spot.

ISSN:0031-9171    

DOI:10.1063/1.865149

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Three‐dimensional computational studies of nonlinear resistive megnetohydrodynamic (MHD) instabilities in the reversed‐field pinch are presented. It is found that multihelicity mode coupling effects alter the evolution ofm=1 modes from that obtained in single helicity. Strong mode coupling tom=0 andm=2 is observed. Magnetic island overlap results in stochastic field lines. At low values of the pinch parameter this is confined to the central region of the pinch; for larger values the stochasticity may extend to the wall. Healing of outer flux surfaces is observed as modes peak and relax. Decay of positive toroidal flux is retarded. Impact on confinement is discussed, and connection is made with experimental observations.

ISSN:0031-9171    

DOI:10.1063/1.865151

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

In a torsatron, the ambipolar electric field is obtained by equating the ion and electron fluxes. This formulation, when solved simultaneously with the density and temperature rate equations, gives continuous electric fields but may lead to the radial derivative of the electric field being discontinuous. This unphysical situation arises from the neglect of the finite orbit deviation from the flux surfaces. If the fluxes are calculated to higher order in inverse aspect ratio to include the finite orbit deviation, then a second‐order differential equation is obtained that will give a continuous first derivative for the electric field.

ISSN:0031-9171    

DOI:10.1063/1.865152

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Transport is studied in toroidal geometry by integrating the guiding‐center equations in magnetic coordinates and simulating collisions with a Monte Carlo collision operator. The effects of the ambipolar electric field on diffusion losses are determined for model magnetic fields and the correct magnetic field of the Advanced Toroidal Facility (ATF‐1) stellarator. Comparisons are made of the computed diffusion coefficients and the theoretically predicted values.

ISSN:0031-9171    

DOI:10.1063/1.865153

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A symmetric tandem mirror plugging a long central cell, with plugs stabilized by a hot‐component plasma is considered. The system is taken to have a flat pressure profile with a steep edge gradient. The interaction of the precessional mode with Alfve´n waves generated in the central cell is then considered. This analysis is noneikonal and is valid whenm&Dgr;/r<1 (mis the azimuthal mode number,rthe plasma radius, and &Dgr; the radial gradient scale length) for long‐wavelength radial modes. Without finite‐Larmor‐radius (FLR) effects the precessional mode is always destabilized by the excitation of the Alfve´n waves form≥2. Form=1, it is possible to achieve stabilization with conducting walls. A discussion is given of how FLR affects stabilization of them≥2 long‐wavelength modes and of FLR stabilization of modes described in the eikonal approximation.

ISSN:0031-9171    

DOI:10.1063/1.865154

出版商:AIP    

年代:1985

数据来源: AIP