摘要:

A unified theory of ion‐pressure‐gradient‐driven drift wave instabilities and transport is presented, which ties the long‐wavelength trapped‐ion mode to the moderate‐wavelength hydrodynamic mode in toroidal geometry. An analytic dispersion relation that retains ion drift resonances, and keeps the leading‐order contribution from finite Larmor radius effects and parallel compressibility, is derived. Results indicate that the slab and toroidal branches of these instabilities are of comparable importance, and are both strong candidates to explain the observed anomalous ion loss in toroidal fusion devices. However, it is concluded that in the limit of flat‐density profiles characteristic of H‐mode discharges, the stabilizing influence of perpendicular compressibility is insufficient to corroborate an improvement, if any, inionconfinement quality. Mixing‐length expressions for the fluctuation amplitudes and both electron and ion transport coefficients are derived. Results also indicate that the heretofore experimentally observed favorable current scaling of the energy confinement time may saturate in low ion‐collisionality discharges. Finally, it is shown that a population of energetic trapped particles, such as those that may be produced during radio frequency or perpendicular neutral beam heating, can significantly exacerbate the instability. Several suggestions for experiments are made to help in differentiating among various anomalous transport scenarios.

ISSN:0899-8221    

DOI:10.1063/1.859206

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The spatial structure of resistive pressure‐gradient‐driven turbulence is studied analytically with renormalized two‐point spectrum equations and numerically by multihelicity nonlinear calculations. The wavenumber spectra for the pressure fluctuations and electrostatic potential fluctuations have been calculated with spectral analysis techniques. The least‐squares fit of the numerically calculated wavenumber spectrum to a power law yields a pressure fluctuation spectrum ⟨p˜2⟩m∼m−(2.4±0.4)and an electrostatic potential fluctuation spectrum ⟨&fgr;˜2⟩m∼m−(4.3±0.3). These results agree with the predictions of the analytic theory. The power‐law decay indexes of energylike spectra show the three‐dimensionality of resistive pressure‐gradient‐driven turbulence, even in a plasma with a strong axial magnetic field. This characteristic of resistive fluid turbulence arises from the important role of the resistivity as an integral part of plasma turbulence and differentiates the resistive plasma turbulence from the homogeneous fluid turbulence.

ISSN:0899-8221    

DOI:10.1063/1.859090

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The response of a shock front to arbitrary small perturbations can be calculated analytically. Such rippled shock front solutions are useful for determining the accuracy of hydrodynamic simulation codes such aslasnex[Comments Plasma Phys. Controlled Fusion2, 51 (1977)], which are used to compute perturbation growth in inertial fusion targets. Thelasnexfractional errors are of order &kgr;2L2, where &kgr; is the transverse wavenumber of the perturbation, andLis the largest zone dimension. Numerical errors are about 25% for a calculation using 26 zones per transverse wavelength.

ISSN:0899-8221    

DOI:10.1063/1.859091

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Electron trapping by intense wave electric fields can alter the power deposition of electron‐cyclotron waves in a tokamak when high‐power sources are employed. The effect of wave trapping is examined in a ray‐tracing study that utilizes plasma and wave parameters appropriate for the Microwave Tokamak Experiment (MTX) [National Technical Information Service Document No. DE‐88016919 (1986)]. It is found that while wave trapping does result in some degradation in the rate of power deposition, single‐pass power deposition is expected to remain significant in MTX. In examining current drive for MTX, the influence of electron trapping in the magnetic wells of the tokamak equilibrium field is included. Relativistic and magnetic trapping effects reduce the driven current by 25% to 50%. This initial study does not include the effects of gradients in the magnetic field and wave vector and therefore provides lower bounds for the power deposition and driven current.

ISSN:0899-8221    

DOI:10.1063/1.859092

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Bootstrap currents in the low collisionality regime in nonaxisymmetric toroidal plasmas are calculated analytically using a model drift kinetic equation. The results obtained using the analytic expression are compared with those calculated from the numerical solutions of the drift kinetic equation. Qualitatively and quantitively, the results are in reasonable agreement.

ISSN:0899-8221    

DOI:10.1063/1.859093

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The nonlinear coupling coefficient and the energy transfer associated with three‐wave interactions are computed from measured data of the turbulent edge plasma of the Texas Experimental Tokamak(TEXT) [Nucl. Technol. Fusion1, 479 (1981)]. The results show the presence of three‐wave interactions. The interactions cause energy to cascade away from the dominant waves of the spectrum primarily toward lower, but also toward higher frequencies. The results are obtained with a new digital spectral analysis technique based on the estimation of higher‐order cumulants. The method is discussed and tested on a simulation experiment. The same technique is useful for neutral fluids as well.

ISSN:0899-8221    

DOI:10.1063/1.859082

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Fluctuations in electric potential, electron pressure, and their relative phase have been measured in the RENTOR tokamak [Phys. Rev. Lett.55, 2417 (1985)] using a heavy ion beam probe. Between 70 and 200 kHz, pressure fluctuation levels ofp˜/p∼0.04 and potential fluctuation levels ofe&fgr;˜/Te=0.08–3 have been observed. The phase angle between the pressure and potential fluctuations is approximately 25°. The heat transport by the observed fluctuations is not enough to account for the observed heat loss at the plasma edge. The RENTOR results are compared with measurements on the TEXT (J. Forster, Ph.D. thesis, Rensselaer Polytechnic Institute, 1987) and ISX‐B [Phys. Rev. Lett.59, 1301 (1987)] tokamaks and with drift wave and rippling mode theories.

ISSN:0899-8221    

DOI:10.1063/1.859083

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

An incompressible fluid model of the ablative Rayleigh–Taylor instability [Phys. Fluids29, 2067 (1986)] is generalized to include self‐consistent diffuse boundaries. With diffuse boundaries the incompressible model is found to be in excellent agreement with a number of previous stability studies of laser ablation. The present theory can predict the scaling of the instability cutoff over an extended parameter range and its dependence on the heat conduction law. It is found that more favorable stability behavior can be obtained both for weak and strong thermal diffusion. Furthermore a strong dependence of the stabilization mechanism on the functional form of the heat conductivity is indicated. Representative conditions for laser ablation are identified and discussed in detail.

ISSN:0899-8221    

DOI:10.1063/1.859084

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The observation of an anti‐Stokes satellite in the spectrum of light backscattered from a CO2laser plasma is reported. Its origin is found to be Thomson scattering of the incident light from a counterpropagating mode‐coupled plasma wave. The parent electron and ion waves in the mode‐coupling process were driven by stimulated Raman and Brillouin backscattering. The parent and daughter plasma waves were detected by ruby laser Thomson scattering. A computer simulation modeling the experiment shows further cascading of the Stokes backscattered light to lower frequencies, apparently a result of its rescattering from another, higher phase velocity, counterpropagating coupled mode. Comparisons with theoretical predictions are presented.

ISSN:0899-8221    

DOI:10.1063/1.859085

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Previous absolute instability results for significant growth from a parametric instability involving oppositely directed modes coupled by a uniform pump with phase inflection coupling (&Dgr;k=k‘x2/2) are extended to higher modes and to thresholds. The results are applied to stimulated Raman scattering experiments done with exploding foils.

ISSN:0899-8221    

DOI:10.1063/1.859086

出版商:AIP    

年代:1989

数据来源: AIP