摘要:

Radial electric fields may be built up in a tokamak by several mechanisms such as nonambipolar particle transport or loss, or the inhomogeneous deposition of electric charge which occurs as a result of the injection of fast neutral atoms. The initial effect of the radial fields is to produce a poloidal rotation of the plasma. Such rotation, however, subjects the moving elements of the plasma to energy dissipation by magnetic pumping, which damps the rotation in a period of the order of the ion‐ion collision time. The problem is analyzed for the “plateau” and “banana” regimes by applying the drift kinetic equation, with a simple relaxation collision term, to a slab‐model low‐&bgr; plasma. The calculation may be more generally applied to the problem of momentum dissipation for any low‐&bgr; long‐mean‐free‐path plasma in a periodic or stochastic magnetic field.

ISSN:0031-9171    

DOI:10.1063/1.1694506

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

It is shown that the loading of a Stix coil by ion‐cyclotron wave production in plasma, which exhibits a second maximum previously reported to be anomalous, can be explained in detail by taking into account the plasma density profile. Data from a number of experiments show that the efficiency for heating the plasma by wave absorption is a monotonically increasing function of density. The reduced heating efficiency observed at the second loading maximum relative to the first can be attributed to damping of the waves responsible for the second maximum in the lower density surface region of the plasma column.

ISSN:0031-9171    

DOI:10.1063/1.1694507

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A new dispersion relation for an unbounded degenerate electron plasma imbedded in a superstrong magnetic field is derived on the basis of the Canuto‐Chiu equation of state. The properties of the various types of waves are discussed for two density regimes of astrophysical interest. Propagation parallel and perpendicular to the magnetic field are examined in detail.

ISSN:0031-9171    

DOI:10.1063/1.1694508

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

New steady‐state solutions are derived which describe electromagnetic waves strong enough to make plasma ions and electrons relativistic. A two‐fluid model is used throughout. The following solutions are studied: (1) Linearly polarized waves with phase velocity much greater thanc; (2) arbitrarily polarized waves with phase velocity nearc, in a cold uniform plasma; (3) circularly polarized waves in a uniform plasma characterized by a scalar pressure tensor. All of these waves are capable of propagating in normally overdense plasmas, due to nonlinearities introduced by relativistic effects. The propagation of relativistically strong waves in a density gradient is examined, for the example of a circularly polarized wave strong enough to make electrons but not ions relativistic. It is shown that such a wave propagates at constant energy flux despite the nonlinearity of the system. However, nonlinear effects can greatly increase the maximum plasma density at which a relativistically strong wave can propagate. Applications to laser‐plasma interactions and to pulsar environments are discussed.

ISSN:0031-9171    

DOI:10.1063/1.1694509

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A dense argon plasma(n e = 4 × 1018cm − 3, KT = 4 eV)is created and allowed to expand either into a vacuum or into a low density, partially ionized plasma. Expansion into a vacuum is shown to be dominated by electric‐field effects which accelerate ions to much higher energies(E ≲ 180 eV)than the original thermal energy. Expansion into a low density(n e = 1 × 1013cm − 3)10% ionized plasma of the same species was dominated by resonant charge exchange giving the appearance of momentum transfer. Expansion into a hydrogen plasma shows essentially complete momentum transfer as in a blast wave. Expansion of a hydrogen plasma into an ambient argon plasma shows spatially separated regions in which the hydrogen appears to collisionally snowplow the argon plasma.

ISSN:0031-9171    

DOI:10.1063/1.1694510

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A model of a neutralized electron beam in which the electrons make helical orbits about the axis is described. This differs from previous models in that there is no longitudinal field or azimuthal current. Three particular cases, corresponding to (1) uniform charge density in a solid beam, (2) uniform current density in a solid beam, and (3) uniform charge density in a hollow beam are analyzed. In none of these configurations is there a current limit, and all the electrons move in the forward direction.

ISSN:0031-9171    

DOI:10.1063/1.1694511

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The wave spectrum of longitudinal electrostatic fluctuations of a beam‐plasma system has been studied in the regime below the threshold for exponentially growing waves. The observed wave spectrum consists of a series of triplets, one set for each natural mode of the magnetized, cylindrical, axially bounded plasma column. The lineshape and intensity of the triplets are in good agreement with a simple theory based on the linearized dispersion relation.

ISSN:0031-9171    

DOI:10.1063/1.1694512

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The excitation and propagation of electron waves in a plasma have been studied experimentally in a low‐density and large‐volume plasma. For frequencies larger than the electron Langmuir frequency, an electron plasma wave was observed which is predicted by the linear theory for a Maxwellian plasma. For smaller frequencies, free‐streaming electron or ballistic signals are observed. For frequencies close to the electron Langmuir frequency, both the electron plasma wave and the free‐streaming electron are excited and show interference patterns. These observations are compared with the theoretical predictions. The effect of a sheath formed around a transmitter on the free‐streaming electron is also discussed.

ISSN:0031-9171    

DOI:10.1063/1.1694513

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The interference structure near the resonance cone of an oscillating point charge in a warm magnetized plasma is investigated theoretically, using the quasistatic approximation and neglecting ion motion. Depending on the frequency and plasma parameters, the interference structure appears inside, outside, or on both sides of the resonance cone. For frequencies less than both the plasma and cyclotron frequencies, the structure lies inside the resonance cone except for frequencies near the cyclotron frequency where the amplitude is small because of cyclotron damping. For frequencies between the upper‐hybrid frequency and the larger of the cyclotron and plasma frequencies, the structure lies outside the resonance cone provided the frequency and angle are sufficiently removed from the upper‐hybrid frequency and 90°, respectively. A simple expression for the angular interference spacing is derived.

ISSN:0031-9171    

DOI:10.1063/1.1694514

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A theory of nonlinear plasma wave propagation is presented which contains, as particular cases, both the nonlinear Schro¨dinger equation for coherent waves and the kinetic wave equation for weak plasma turbulence. Fluctuations are represented as a superposition of “micro” wave packets, with finite spread but negligible overlap in wavenumber and frequency. For the case of coherent wave propagation a nonlinear Schro¨dinger equation is derived, generalized over precious versions in that linear Landau damping nonlinear frequency shift, nonlinear damping, and three‐dimensional effects are all included, as well as the non‐local, non‐Markovian interaction characteristic of this equation. In the case of weak plasma turbulence, the kinetic wave equation is generalized to include self‐interaction of the micro packets, which, just as in the coherent case, results in non‐local, non‐Markovian terms, not heretofore considered in weak turbulence formulations.

ISSN:0031-9171    

DOI:10.1063/1.1694515

出版商:AIP    

年代:1973

数据来源: AIP