摘要:

Efficient techniques for computing axisymmetric non‐neutral plasma equilibria are described. These equilibria may be obtained either by requiring global thermal equilibrium, by specifying the midplane radial density profile, or by specifying the radial profile of ∫n dz. Both splines and finite‐differences are used, and the accuracy of the two is compared by using a new characterization of the thermal equilibrium density profile which gives a simple formula for estimating the radial and axial gradient scale lengths of thermal equilibria. It is found that for global thermal equilibrium 1% accuracy is achieved with splines if the distance between neighboring splines is about two Debye lengths while finite differences require a grid spacing of about one‐half Debye length to achieve the same accuracy.

ISSN:0899-8221    

DOI:10.1063/1.860594

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The global asymptotic matching equations for multiple coupled resistive modes of arbitrary parity in a cylindrical plasma are derived. Three different variational principles are given for the outer region matching data, while the inner region analysis features a careful treatment of the symmetry‐breaking effect of a gradient in the equilibrium current for a zero‐&bgr; slab model. It is concluded that the usual constant‐&psgr; result remains valid and constrains the matrix matching formalism. The dispersion relation is compared with initial value calculations of a double tearing mode when there are small relative rotation velocities between the rational surfaces. In treating differential rotation within the asymptotic matching formalism, flow is ignored in the outer region and is assumed to affect the inner response solely through a Doppler shift. It is shown that the relative rotation can have a strong stabilizing effect by making all but one rational surface effectively ideal.

ISSN:0899-8221    

DOI:10.1063/1.860595

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Similarity solutions to a problem in radiative magnetogasdynamics with strong shocks are presented. Group theoretic methods are used to obtain a condition on the shock Cowling number, and to characterize the state dependent form of the gas absorption coefficient for which the self‐similar solutions are admitted. Numerical calculations have been performed to determine the value of the self‐similar exponent and the profiles of the flow variables, which enable one to assess the influence of thermal radiation, the magnetic field strength, and the adiabatic heat exponent on the flow pattern.

ISSN:0899-8221    

DOI:10.1063/1.860596

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Thermal corrections toE×Bdrifts cause small structures in pure electron plasmas to smear. This smearing breaks the strict analogy between the behavior of pure electron plasmas and the behavior of two‐dimensional inviscid fluids. The causes and consequences of this smearing are discussed, a criterion for the validity of the plasma/fluid analogy is constructed, and experimental examples of the failure of the analogy are presented. The criterion indicates that fluid‐like behavior can persist to scale lengths far smaller than the normal ‘‘collective’’ behavior limit.

ISSN:0899-8221    

DOI:10.1063/1.860546

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Discussion and applications are presented for two approaches for estimating the effects of scattering of electromagnetic waves by turbulent density fluctuations in tokamaks. Ordinary‐mode waves propagating nearly perpendicular to the equilibrium magnetic field are considered. The multiple‐scattering approach provides analytic results for the angular and spatial spreading of a microwave beam by the turbulence. The single‐scattering approach yields numerical results and is derived by a compact technique involving Wigner functions. Both approaches are applied to idealized tokamaks to clarify relationships between the approaches and to test limits of applicability of the multiple‐scattering approach.

ISSN:0899-8221    

DOI:10.1063/1.860547

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A drift‐kinetic Eulerian Vlasov code, with fluid equations for the ions, is developed to study the problem of the injection of an electron beam into a two‐dimensional magnetized plasma, often referred to as direct current (dc) helicity injection. The diffusion of electrons across a magnetic field in the presence of a beam–plasma instability is studied. The case of a magnetic field tilted with respect to the beam direction is considered. The competition between the velocity shear Kelvin–Helmholtz (KH) and the beam–plasma (BP) instabilities is investigated in order to analyze the plasma heating and current drive mechanism induced by the beam injection. The KH instability generates low‐frequency plasma convection motion associated withcE×B/B2drift. In particular, the diffusion coefficientsDyandDv∥describing, respectively, the anomalous diffusion process induced in space across the magnetic field by the KH instability, and the velocity diffusion process due to the kinetic effects induced in velocity space along the magnetic field by the BP instability, are computed using test‐particle diagnostics. In the present Cartesian model, it is found thatDy=Dv∥ tan2 &thgr;/&ohgr;ce2where &thgr; is the angle between the magnetic field and thexaxis. This relation which links the electron dynamics in thex‐yreal space and in thex‐v∥phase space is verified by the numerical code. The Vlasov code provides a powerful tool to study particle diffusion in space and in phase space, especially in the low‐density regions of the distribution function.

ISSN:0899-8221    

DOI:10.1063/1.860548

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The fast penetration of a strong magnetic field into a plasma, caused by the Hall effect, is studied. The phenomenon is likely to govern the early evolution of the magnetic field not only in two‐dimensional geometry, to which previous studies were restricted, but also in three dimensions. This penetration mechanism is suppressed, if both the plasma and electrodes are collisionless,vAe&tgr;e≳a, wherevAeis the electron Alfve´n velocity, &tgr;e−1the collision frequency, andathe characteristic space‐scale. However, the collisionless penetration can occur in the case of a resistive cathode. The self‐consistent effect of ion motion is shown to be of importance only in a very special geometry. Then the penetration speed is limited by the valueVA(a&ohgr;pi/c)−1/3, whereVAis the Alfve´n velocity andc/&ohgr;pithe ion skin depth.

ISSN:0899-8221    

DOI:10.1063/1.860549

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The weak turbulence theory of Langmuir waves in a one‐dimensional, one‐species plasma is discussed. Analytic calculations using the theory of two‐point correlations show that in the weak turbulence regime, &tgr;ac≪min(&tgr;tr,&ggr;−1k) (where &tgr;acis the field autocorrelation time and &tgr;tris the particle decorrelation time), the nonlinear enhancement of the mode growth rate &ggr;kbeyond the linear, Landau growth rate &ggr;kLis small, additive, and higher order in the weak turbulence expansion parameter. This result thus supports the validity of the quasilinear theory for Langmuir wave turbulence, and disagrees with the predictions of Adam, Laval, and Pesme [Phys. Rev. Lett.43, 1671 (1979)], which indicate a non‐negligible, multiplicative enhancement in the regime &tgr;ac≪&tgr;tr≪&ggr;−1k. Analysis shows that their result comes from the use of an invalid source term for the fluctuations.

ISSN:0899-8221    

DOI:10.1063/1.860550

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Experiments are reported on the ion thermal transport due to the ion‐temperature‐ gradient‐driven instability (ITG mode) and its transport scaling properties with respect to instability parameters like fluctuation leveln˜/niand linear growth rate as well as the drive parameter &eegr;i(=∂ ln[Ti]/∂ ln[ni]) in the Columbia Linear Machine [Phys. Fluids26, 1044 (1983)]. The measured local ion thermal conductivity &khgr;⊥(r) is highly anomalous and strongly correlated with the radial profile of the ITG mode. The linear scaling of the averaged thermal conductivity ⟨&khgr;⊥(r)⟩ with the averaged mode fluctuation level ⟨n˜/ni⟩ and linear growth rate indicates strong turbulence‐type scaling. The scaling of &khgr;⊥with the drive parameter &eegr;iis offset linear.

ISSN:0899-8221    

DOI:10.1063/1.860551

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Possible nonlinear effects in electron‐cyclotron plasma production and heating by microwave radiation are analyzed. They include nonlinear regimes of electron acceleration in strong microwave fields under cyclotron resonance conditions, nonstationary regimes of microwave beam self‐focusing, and some parametric processes. Presented results may be of importance for predictions of plasma response to electron‐cyclotron resonance (ECR) heating or preionization by powerful radiation.

ISSN:0899-8221    

DOI:10.1063/1.860552

出版商:AIP    

年代:1993

数据来源: AIP