摘要:

The mechanism of electron trapping in E×B guiding center motion is proposed as the mechanism for absolute stabilization of drift‐cone modes in mirror geometry. The calculated amplitudes are shown to be in reasonable agreement with experimental results in present mirror machines.

ISSN:0031-9171    

DOI:10.1063/1.861983

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A method for computing the spectral emissivity of spontaneous synchrotron radiation is discussed. The Klimontovich formalism in plasma kinetic theory is adopted in which an ensemble average of the microscopically emitted power is considered. The present method clarifies the meaning of the random phase approximation which is imposed in several existing theories of synchrotron radiation. Both the effects of dielectric polarization and two‐particle correlations are included in the present discussion. The theory is applied to the case of a plasma in thermal equilibrium, for which it is shown that the effect of pair correlations on the emissivity vanishes. On the other hand, the effect of dielectric polarization is studied numerically for a wide range of parameters.

ISSN:0031-9171    

DOI:10.1063/1.861984

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The relation between the particle dynamics of an intense relativistic electron beam and its accompanying microwave radiation has been explored. A diagnostic has been developed which makes use of the strong forward directed x‐ray radiation pattern of relativistic electrons colliding with a lowZthin target foil, to determine the transverse electron momentum of the beam as it moves along a magnetic field. The transverse momentum of the beam electrons is controlled both by a magnetic undulator, consisting of spaced iron rings similar to those used in previous cyclotron maser experiments, and by a carefully wound electromagnet consisting of alternating dipoles. The effect of relative undulator strength on the beam momentum distribution is determined, together with total microwave power as measured by a calorimeter. The results, which are interpreted with the aid of a numerical model, indicate a positive correlation between perpendicular momentum and radiated power. The spread in perpendicular velocity of the beam electrons was found to depend on the type of undulator used, the relative undulator strength and also influences the amount of radiated power.

ISSN:0031-9171    

DOI:10.1063/1.861985

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Equations have been derived which describe the nonlinear evolution of standard drift waves (driven by inverse Landau damping) and of dissipative trapped electron modes. Assuming that all but then=0 modes are shear stabilized, it is shown that the nonlinear equations admit eigenfunctions of the same form as the linear equations with, however, the shear lengthLs=q/(&egr;dlnq/dr) replaced by another lengthls<Ls.lsdecreases with increasing turbulence thereby stabilizing the mode. The turbulence level and the diffusion coefficient are self‐consistently calculated. In the case of the standard drift wave, good agreement is found with experimental results in linear devices. In the case of the trapped electron mode, estimates obtained with parameters derived from published profiles of ST tokamak discharges are quite reasonable. Stabilization arises through nonlinear diamagnetic drifts.

ISSN:0031-9171    

DOI:10.1063/1.861986

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Analytic solutions to the problem of linear wave conversion in a cold, unmagnetized, collisionless plasma are obtained for nearly all angles of incidence. The resulting absorption coefficients are in excellent agreement with numerical work in the appropriate limits and differences in previous solutions are reconciled. The warm plasma equations are also solved, and the independence of the absorption coefficient to thermal effects verified. The singularities neglected by Piliya are properly treated by viewing the frequency dependence as arising from a Laplace transform.

ISSN:0031-9171    

DOI:10.1063/1.861987

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The rate of energy absorption for electrons in a plasma is calculated from the emission, including plasma effects through the index of refraction. The net absorption is obtained for the case of propagation perpendicular to an applied dc magnetic field. The dispersion relation for cyclotron harmonic waves is solved numerically to obtain wavenumbers as functions of excitation frequency. This gives the index of refraction required to find the net absorption rate. Spectra for various temperatures and densities are found by integration over the electron velocity distribution.

ISSN:0031-9171    

DOI:10.1063/1.861988

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The slow nonresonant beat disturbance (&ohgr;2−&ohgr;1, k2−k1) generated by two obliquely propagating ion acoustic waves has been observed. The beat signal wavenumber, direction, and speed agree with predicted values. The beat signal amplitude, normalized to the product of the driving wave amplitudes, exhibits a maximum when the beat signal speed is approximately equal to one‐half the ion thermal speed. The energy transfer between the two driving waves has also been observed.

ISSN:0031-9171    

DOI:10.1063/1.861968

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Two unstable modes were observed in the average minimum‐Bregion of the levitated octupole operating with a weak toroidal field (safety factor of approximately 0.25) and collisionless ions. One mode propagated in the electron diamagnetic drift direction and the other mode propagated in the ion diamagnetic drift direction. The frequencies of the modes were much greater than the ion detrapping collision frequency and slightly less than the trapped ion bounce frequency. The electron collisionality was intermediate between the collisionless trapped ion mode and the dissipative trapped ion mode regimes. Density fluctuation levels from 5% to 50% and enhanced transport approaching Bohm diffusion were the manifest effects of the instabilities. When the ion collisionality was increased by cooling the ion temperature, the unstable fluctuations were not seen.

ISSN:0031-9171    

DOI:10.1063/1.861969

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The time evolution of an initially uniform slightly underdense (&ohgr;e≲&ohgr;) plasma in a resonant cavity has been studied using two‐dimensional electromagnetic simulations. The ponderomotive force compresses plasma into the nodes of the applied radio frequency field. The plasma buildup at the nodes terminates either when the plasma pressure increases to equal the field pressure or when phase space breaking occurs. Explanations of the density buildup and tail formation of the particle distribution functions are provided.

ISSN:0031-9171    

DOI:10.1063/1.861970

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The transverse displacement of free shear layers as inferred from von Ka´rman’s condition is estimated analytically uisng conventional bondary layer theory. The displacement of the dividing streamline can be expressed in terms of the maximum viscous stress present within the mixing region.

ISSN:0031-9171    

DOI:10.1063/1.861971

出版商:AIP    

年代:1977

数据来源: AIP