摘要:

An eigenmode equation for collisional electrostatic drift waves in general axisymmetric toroidal geometry is derived and solved numerically for a low‐&bgr; spheromak. In the calculation of the density responses, the ions are treated as a cold fluid, and the electrons are assumed to be isothermal. The electron–ion collision operator is approximated by a friction term in the parallel component of the electron momentum equation, and the perturbation analysis includes the self‐consistent equilibrium electron current dynamics. Large toroidal mode numbers are assumed and use is made of the simplifying ballooning mode representation. The main destabilizing mechanism found here comes from electron–ion collisions. For the parameters considered, the mode frequency and growth rate are hardly affected by the equilibrium current driving terms.

ISSN:0031-9171    

DOI:10.1063/1.863693

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Particle simulations and analytic theory confirm the experimental observation of preferential ion acceleration and heating by an inductive electric fieldEdcin picket‐fence geometry. The ions which are unmagnetized over most of the current channel are freely accelerated by the inductive field; the magnetized electrons are tied to the field lines and do not run away as long as the bindingev×B/cforce is greater than the detrapping inductive forceeEdc. Consequently, most of the current is carried by the ions which are also Ohmically heated.

ISSN:0031-9171    

DOI:10.1063/1.863694

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The Kruskal–Oberman energy principle is used to calculate the stability to flutes of an axisymmetric mirror. Marginally stable pressure profiles are calculated for the Lamex device.

ISSN:0031-9171    

DOI:10.1063/1.863695

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The stability of straight helically‐symmetric low‐&bgr; systems is studied. Two families of equilibria are investigated which differ from each other by the ordering of the physical variables in &bgr;. The energy principle as well as eigenmode analysis are used in order to check the stability properties of the equilibria. It is found that low shear systems are stable to interchangelike modes. It is shown that interchange stability is necessary and sufficient for stability. Thus, low shear, zero net current configurations are found which are stable. Systems with arbitrary shear are found to be stable but also to have neutrally stable modes which are localized around rational flux surfaces.

ISSN:0031-9171    

DOI:10.1063/1.863696

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Mathematical techniques are described that facilitate the reduction of the stability problem of a toroidal free‐boundary high‐&bgr; tokamak equilibrium with skin currents to one that is basically one‐dimensional. This includes the conformal mapping of the simply connected plasma region onto a circular disk and the conformal mapping of the doubly connected vacuum region onto an annulus by means of the Theodorsen and Garrick nonlinear integral equations. Henrici’s method of constructing the discretized Hilbert transforms for periodic functions on the boundaries of these domains provides both the basis for constructing the mappings and the tool for the study of the perturbations. The methods are applied to problems of two‐dimensional potential flow with a discontinuity of which the stability of sharp‐boundary high‐&bgr; tokamaks is just a special case.

ISSN:0031-9171    

DOI:10.1063/1.863697

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Using the techniques of Hilbert transforms and conformal mapping, the stability problem of a toroidal free‐boundary high‐&bgr; tokamak equilibrium with a skin current is reduced to a one‐dimensional problem for which a new variational principle is derived. The minimization is carried out numerically and a complete scan of parameter space is carried out. The stability limit is qualitatively different from the one obtained in the usual fixed‐boundary model without a wall. Rather than a more severe, a less severe limitation on the plasma current is obtained. It is shown that the Kruskal–Shafranov limit may be surpassed when the value of &bgr; is sufficiently high and the wall is sufficiently close to the plasma.

ISSN:0031-9171    

DOI:10.1063/1.863698

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Equilibrium and stability properties of an intense electron ring located at the midplane of an externally applied mirror field are investigated within the framework of the linearized Vlasov–Maxwell equations, including the important influence of equilibrium self‐fields and an applied fieldBext0&thgr;in the toroidal direction. It is assumed that the ring is thin and that &ngr;/&ggr;b≪1, where &ngr; is Budker’s parameter and &ggr;bmc2is the characteristic electron energy. Equilibrium and stability properties are calculated for the choice of equilibrium distribution function in which all electrons have the same value of energy in a frame of reference rotating with angular velocity &ohgr;bin the minor cross section of the ring, and a Lorentzian distribution in canonical angular momentumP&thgr;. Negative‐mass and resistive‐wall stability properties are calculated, and a closed dispersion relation is obtained for the case where the ring is located inside a toroidal conductor with finite resistivity and minor radiusacmuch less than the major radiusR0. One of the most important features of the stability analysis is that the negative‐mass instability in a high‐current ring can be stabilized by equilibrium self‐field effects in circumstances where the self‐fields are sufficiently intense. Moreover, a modest spread &Dgr; in canonical angular momentum can stabilize the resistive‐wall instability.ufoff

ISSN:0031-9171    

DOI:10.1063/1.863699

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Transport of neutrals in a plasma, consisting of two species of ions and neutrals, across a plane plasma slab bounded between the wall and hot plasma is investigated using a kinetic approach. Analytical expressions for the neutral density profile and the velocity distribution functions have been obtained. For impurity elements like He, Ne, and Ar for temperaturesT<10 eV, the neutral transport is controlled jointly by electron ionization and charge exchange and the penetration depth for neutral atoms of these elements is found to be somewhat larger than the penetration depth for neutral hydrogen atoms. In the temperature range 20 eV<T<100 eV the penetration of both the neutral species is governed mainly by electron ionization and the penetration depth for neutral hydrogen atoms is found to be nearly equal to that for neutrals of these elements. It is also noted that the impurity content in the plasma phase affects the transport of impurity neutrals weakly when 20 eV<T<100 eV and strongly forT<10 eV.

ISSN:0031-9171    

DOI:10.1063/1.863668

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Experimental tests of anE˜×B˜ plasma sweeper, designed to control the plasma density near the mouth of a phased waveguide array, are described.

ISSN:0031-9171    

DOI:10.1063/1.863669

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

An experimental study of radial transport in the Tandem Mirror Experiment is reported here. Plasma parameters were measured in a series of well‐diagnosed plasma discharges. A negative electric current (80±40 A within a 30‐cm radius) flowed to the end wall, implying an equal radial loss of plasma ions. The axial losses of plasma ions were 100 A from the same volume. The nonambipolar radial ion flux was of the same order as the flux resulting from resonant‐neoclassical and ion‐neutral transport, but the uncertainties are large. The ambipolar radial transport (of both ions and electrons) was investigated by comparing the observed end losses with calculations of the plasma fueling by gas penetration and neutral beams. The ambipolar radial losses are probably smaller than the loses through other processes and may be as small as the classical losses resulting from Coulomb collisions.

ISSN:0031-9171    

DOI:10.1063/1.863670

出版商:AIP    

年代:1982

数据来源: AIP