摘要:

The marginal stability of long thin field‐reversed plasmas to axisymmetric tearing modes is examined. It is found that stability improves greatly as flux is excluded from the plasma. Such naturally occurring states may account for the lack of tearing mode activity in many experiments. Consideration is also given as to whether, in three dimensions, the tearing mode is an instability or a condition for the breakdown of equilibrium. An example is given that demonstrates that it is an instability. Idealized analytic results and more realistic numerical results are presented.

ISSN:0031-9171    

DOI:10.1063/1.863759

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A comprehensive analysis of low‐frequency, high‐toroidal‐mode‐number linear eigenmodes for tokamaks is presented. The most significant new features of this stability study are that the calculation is interfaced with a general numerical magnetohydrodynamic equilibrium, and that it is fully electromagnetic. The ballooning formalism is employed and all important kinetic effects, including those of trapped particles, are retained. In particular, the familiar trapped‐electron drift‐wave frequency regime is considered and results are presented for three sequences of artificial equilibria; one of increasing &bgr;(≡plasma pressure/magnetic pressure) values; one of varying equilibrium shape, from inverse‐D to circular to normal‐D; and one of increasing vertical ellipticity. The analysis is then applied to a realistic (self‐consistent) high‐&bgr; equilibrium generated with data obtained from the ISX‐B tokamak experiment. Here it is found that for the usual trapped‐electron branch, kinetic microinstabilities appear to be present over a wide range of toroidal mode numbers.

ISSN:0031-9171    

DOI:10.1063/1.863760

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The interaction of three nonlinearly coupled drift waves is investigated for the occurrence of stochastization of the phases and the applicability of the random phase approximation. The drift wave nonlinearities include the E×B and polarization drift couplings for waves that are linearly unstable for appropriate values of the perpendicular wavenumber. The conservation properties and sample numerical solutions for the exact three wave interaction are given along with the conservation properties and solutions of the corresponding random phase approximation equations.

ISSN:0031-9171    

DOI:10.1063/1.863761

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A nonlinear gyrokinetic formalism for low‐frequency (less than the cyclotron frequency) microscopic electromagnetic perturbations in general magnetic field configurations is developed. The nonlinear equations thus derived are valid in the strong‐turbulence regime and contain effects due to finite Larmor radius, plasma inhomogeneities, and magnetic field geometries. The specific case of axisymmetric tokamaks is then considered and a model nonlinear equation is derived for electrostatic drift waves. Also, applying the formalism to the shear Alfve´n wave heating scheme, it is found that nonlinear ion Landau damping of kinetic shear‐Alfve´n waves is modified, both qualitatively and quantitatively, by the diamagnetic drift effects. In particular, wave energy is found to cascade in wavenumber instead of frequency.

ISSN:0031-9171    

DOI:10.1063/1.863762

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A linear kinetic analysis of the universal drift mode, valid for arbitrary values of &bgr;( = 8&pgr;p/B2), is presented. The three high‐&bgr; effects on the universal, ∇Bdrifting particles, coupling to the drift Alfve´n wave and compressional magnetic fluctuations are examined in detail. For small values of &bgr;, the drift wave behavior is dominated by coupling to the Alfve´n wave, while for &bgr;∼O(1) the wave behavior is determined by ∇Beffects. For most plasma and wave parameters, the mode is stable for &bgr;i⩾7%. The stabilization mechanism is the Alfve´n induced frequency downshift which reduces the parallel phase velocity of the wave until the (slightly) ∇Bbroadened ion Landau resonance damps the wave. For &eegr;e( = ∂ ln Tc/∂ ln N)≳0, a peculiar case is found where the mode remains unstable for &bgr;i⩽0(50%). This is caused by the ∇Bfrequency upshift coupled with inverse transit time damping.

ISSN:0031-9171    

DOI:10.1063/1.863763

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The Grad–Shafranov equation for an ideal magnetohydrodynamic axisymmetric toroidal configuration is solved analytically in a local polar coordinate system using a novel method which produces solutions valid up to the second order in the inverse aspect ratio expansion.

ISSN:0031-9171    

DOI:10.1063/1.863764

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A method is given for expressing the magnetic field strength in magnetic coordinates for an arbitrary toroidal, scalar pressure, equilibrium with magnetic surfaces. The field strength in magnetic coordinates is central to the study of equilibrium, stability, and transport in asymmetric plasmas. While doing these calculations, it is assumed that the plasma equilibrium is known.

ISSN:0031-9171    

DOI:10.1063/1.863765

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The possibility of curtailing trapped particle modes and reducing ripple diffusion in a tokamak reactor by external turbulence is investigated. A ’’classical’’ analysis of the problem shows that the power level required is low for ripple detrapping, but it is very high for suppression of trapped particle modes. If, however, strong turbulence effects including clump formation are considered, periodically pulsed turbulence can be used to eliminate trapped particles and significantly reduce the cross‐field diffusion at an average power level which may be acceptable in a reactor.

ISSN:0031-9171    

DOI:10.1063/1.863766

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

An energy‐conserving model of magnetohydrodynamic turbulence is described that predicts both mode coupling and turbulent dissipation. The dissipation takes the form of anomalous resistivity and viscosity due to turbulent magnetic fields. The model predicts a dual cascade of energy to large wavenumbers and magnetic flux to small wavenumbers. Turbulent rearrangement of equilibrium magnetic shear generates resonant fluctuations via a mixing length process. The effect of the turbulence on the disruptive instability in tokamaks is discussed.

ISSN:0031-9171    

DOI:10.1063/1.863767

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

It has been shown by Hazeltine and Ware that the existence of a reasonable high‐Zimpurity species can produce electrostatic trapping and drift comparable to the magnetic effects, assuming that the main plasma components are in the plateau regime. The calculation is extended to the collisional regime, modeling the edge region of the tokamak column and significant modification to the neoclassical impurity transport coefficients is found. A fluid approach is developed and the transport coefficients are found to be nonlinear in density and temperature gradients.

ISSN:0031-9171    

DOI:10.1063/1.863768

出版商:AIP    

年代:1982

数据来源: AIP