摘要:

The adiabatic compression of plasmas with mass rotation is formulated as a variational principle based on some constants of the motion. A numerical code is constructed and Grad’s alternating dimensions method is used. The calculations simulate compression either by increasing the flux outside the plasma or by liner compression. Changes in Mach number and some stability criteria during compression are monitored. Interestingly, the Mach number remains almost constant despite a spin up of the plasma. An extension of the interchange stability criterion for rotating plasmas is developed. Interchange stable equilibria exhibit very high current density near the separatrix and tend to be more elongated. Interchange instability offers a mechanism to generate rotation throughout the plasma.

ISSN:0031-9171    

DOI:10.1063/1.865072

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

In order to lay a foundation for understanding kinetic effects on waves and instabilities in reversed field pinches, three different plasma models are employed to study linear perturbations of uniformly magnetized, infinite, homogeneous, current‐carrying plasmas. Two different types of instability emerge: configuration‐space instabilities driven by the macroscopic current and velocity‐space instabilities driven by the relative drift between electrons and ions parallel toB. The dispersion properties of waves and parallel current and drift‐driven instabilities with frequencies below the ion gyrofrequency are used to establish the physics limitations of the asymptotic guiding center plasma model. This model is then used to investigate parallel drift‐driven instabilities in fully self‐consistent, cylindrically symmetric, radially inhomogeneous equilibria that manifest large parallel currents and strong magnetic shear, as in reversed field pinches. The results of the cylindrical guiding center plasma are compared with those of the current‐carrying infinite plasma to illustrate the effects of the magnetic shear and curvature generated by the equilibrium current. Although quantitative differences appear, the same qualitative features are found in each case. The results illuminate the nature of current‐carrying plasmas. The dispersion properties of shear Alfve´n waves in such a plasma are very different from &ohgr;=k∥cA. Some of the modified shear Alfve´n waves that propagate against the current are destabilized by resonant electrons.

ISSN:0031-9171    

DOI:10.1063/1.865073

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The theory of cross‐field ion streaming instabilities is applied to the parameter regime of the end cells of the upgraded Tandem Mirror Experiment with neutral beam injection. The cross‐field ion drift as well as the electron thermal anisotropyTe⊥>Te∥provides the free‐energy that drives various instabilities. Three instabilities, a nearly perpendicular propagating modified two‐stream instability, an obliquely propagating ion–ion streaming instability, and an obliquely propagating electromagnetic lower‐hybrid instability, have been identified. The first two waves are electrostatic and have the largest growth rate. For the actual operation conditions of the tandem mirror machines, it is found that the ion–ion streaming instability has the largest growth rate. When more energetic neutral beams become available, the two‐stream instability may play the dominant role in the stability of these devices.

ISSN:0031-9171    

DOI:10.1063/1.865074

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Some designs for tandem mirror devices rely on a thermal‐barrier cell, a region of depressed potential located between the central cell and the end plugs. This region of depressed potential relies on, to some extent, an ion distribution function that has two peaks invz(ion velocity parallel to the magnetic axis). Therefore there is a possibility that some ion–ion two‐stream modes can be unstable. Using one‐dimensional models, the stability of model equilibria to electrostatic ion two‐stream modes is considered. The results suggest that for parameters of greatest interest (i.e., for planned experiments), these modes could be stable. Particle simulation techniques are used to examine the nonlinear consequences for those conditions where instability is present.

ISSN:0031-9171    

DOI:10.1063/1.865075

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A low‐beta tandem‐mirror trapped‐particle instability theory is developed for arbitrary azimuthal mode number including the effects of radial equilibrium electric fields. A stability window is seen to exist for inward‐pointing electric fields even when passing electrons bounce beyond passing ions. This stability window can persist at zero radial electric field when the instability drive is sufficiently small. The theory also predicts the possibility of an additional instability whenE×Brotation is present: a rotationally driven trapped‐particle mode.

ISSN:0031-9171    

DOI:10.1063/1.865076

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

When large probes are used to measure plasma properties in tokamak scrape‐off layers, the presence of the probe influences the plasma being measured. A theory is presented for probe interpretation which makes it possible to infer undisturbed values ofTe,Ti,ne, etc. The first requirement in such an analysis is for analytic models of the scrape‐off layer, which can then be modified to allow for the presence of the probe. The present work gives such a model for the collisionless scrape‐off layer, and criteria are stated governing its applicability. Such models may be of use for other applications, e.g., predictions of power loading to limiter surfaces, the magnitude of wall sputtering, etc.

ISSN:0031-9171    

DOI:10.1063/1.865077

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

It is shown that for collisionless transverse magnetosonic shocks, there exists an intermediate range of Mach numbers between the maximum Mach number for transverse resistivity and the onset of significant ion reflection. In this intermediate range, the structure is dominated by a breakdown of the quasineutrality approximation, and longitudinal friction is a simple fluid model for the dissipation mechanism which forms the shock. Applications are discussed for laboratory shocks as well as the Earth’s bow shock.

ISSN:0031-9171    

DOI:10.1063/1.865408

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A new mechanism for the direct generation of electromagnetic radiation by a field‐aligned electron beam is presented. It is shown that, under the condition &egr;c=&ohgr;2p/&ohgr;2c≪1, a weakly relativistic beam can couple linearly the two branches of the extraordinary mode. It is suggested that such a mechanism can offer one more possible source for the auroral kilometric radiation.

ISSN:0031-9171    

DOI:10.1063/1.865078

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Growth rates of negative mass instabilities in conventional and modified betatrons are calculated by analytic methods and by performing three‐dimensional particle simulations. In contrast to earlier work, toroidal corrections to the field equations are included in the analytic model. As a result, good agreement with numerical simulations is obtained. The simulations show that the nonlinear development of the instabilities can seriously disrupt the beam.

ISSN:0031-9171    

DOI:10.1063/1.865079

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A quasilinear model is developed that describes the nonlinear evolution and stabilization of the free electron laser instability in circumstances where a broad spectrum of waves is excited. The relativistic electron beam propagates perpendicular to a helical wiggler magnetic fieldB0=−Bˆ cos k0 z eˆx−Bˆ sin k0 z eˆy, and the analysis is based on the Vlasov–Maxwell equations assuming ∂/∂x=0=∂/∂ yand a sufficiently tenuous beam that the Compton‐regime approximation is valid (&dgr;&fgr;&bartil;0). Coupled kinetic equations are derived that describe the evolution of the average distribution functionG0( pz,t) and spectral energy densityEk(t) in the amplifying electromagnetic field perturbations. A thorough exposition of the theoretical model and general quasilinear formalism is presented, and the stabilization process is examined in detail for weak resonant instability with small temporal growth rate &ggr;ksatisfying ‖&ggr;k/&ohgr;k‖≪1 and ‖&ggr;k/k &Dgr;vz‖≪1. Assuming that the beam electrons have small fractional momentum spread (&Dgr; pz/p0≪1), the process of quasilinear stabilization by plateau formation in the resonant region of velocity space (&ohgr;k−kvz=0) is investigated, including estimates of the saturated field energy, efficiency of radiation generation, etc.

ISSN:0031-9171    

DOI:10.1063/1.865080

出版商:AIP    

年代:1985

数据来源: AIP