摘要:

The steady‐state flow of a conducting fluid between two coaxial rotating disks in the presence of an axial magnetic field is considered for the following conditions: (1) the gapdbetween two disks is very small compared with the radial extension of the disksR; (2) the angular velocity of the disks is not too high, so that the thickness of the Eckman layer &dgr; is still larger than the gapd, (d/&dgr;)1/4≪1; and (3) the magnetic fieldBis moderate so that the corresponding Hartman numberM≪R2/d2. Under these conditions asymptotic solutions to the problem are obtained in terms of the small parameter &Egr;=d/R. The results show that to the lowest‐order approximation, the electric properties of the disks are not important to the flow field, while the magnitude of the magnetic field plays an important role in the equilibrium flow profile.

ISSN:0031-9171    

DOI:10.1063/1.866417

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Electron cyclotron emission from nonthermal electron distributions has been measured with a vertical view and control of multiple reflections. The observed intensities at the first few harmonics provide information that can be used to deduce the electron distribution function. Although harmonic overlap restricts the detail that can be obtained when the distribution is very energetic, a fitting procedure enables useful results to be obtained. The distribution functions during Ohmic runaway and lower‐hybrid current drive and heating are presented. The current‐drive distributions are not inconsistent with theoretical Fokker–Planck calculations, giving perpendicular and parallel ‘‘temperatures’’ around 60 keV and 200 keV, respectively. The runaway cases have quite similar distributions.

ISSN:0031-9171    

DOI:10.1063/1.866418

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

In a linearl=1 stellarator [Phys. Fluids30, 2885 (1987)] internal probes are used to measure the structure and temporal behavior of the plasma and magnetic field. At lower densities (and higher temperatures) diffuse‐profile equilibria are produced that are perturbed by ak≊0 oscillation. At higher densities (and lower temperatures) sharp‐boundary plasmas are produced that are unstable with an exponentially growingm=1,k≊0 mode. Finite Larmor radius (FLR) effects are adduced to explain the absence of the instability in the oscillatory regime.

ISSN:0031-9171    

DOI:10.1063/1.866419

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Very‐high‐energy electrons of up to an energy of ∼2.3 MeV have been observed to be emitted from the hot underdense exploding thin foil plasmas created by 10.6 &mgr;m CO2laser radiation at intensity levels up to ∼4×1014W/cm2. As a supplement to the electron measurements the forward and backward scattered light components were also measured. Correlation of these measurements shows that either Raman scattering or the high‐temperature version of two‐plasmon decay or both, manifesting themselves near the quarter‐critical density region, are responsible for the production of a hot (Th∼135 keV) tail of electrons at least up to energies of 1 MeV. There are no indications that the Raman forward scattering (as distinct from Raman backward scattering) at lower densities plays any significant role. These experimental results are consistent with the results from a l 1/2 ‐dimensional particle‐in‐cell code simulation with a parabolic density profile resembling the experimental conditions. An apparent anomaly is discussed, which is that hot electrons are produced (both in experiments and simulations) at energies higher than the trapping value appropriate to electron plasma waves whose phase velocity is equal to the matching value (C/(3)1/2) at the turning point for the light of half the laser frequency.

ISSN:0031-9171    

DOI:10.1063/1.866420

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Thomson scattering techniques were used to measure the frequency of plasma waves near the quarter‐critical surface in a well‐diagnosed plasma irradiated by a nanosecond CO2laser with intensity ∼1014W/cm2. The frequency &ohgr;pwas shown to be less than &ohgr;0/2, in disagreement with the commonly used estimate &ohgr;p=&ohgr;0/2+ (9)/(8) (ve/c)2&ohgr;0. The theory of Afeyan and Williams [Phys. Fluids28, 3397 (1985)] gives better agreement, and shows that the density scale length is more important than the temperature in determining the frequency shift.

ISSN:0031-9171    

DOI:10.1063/1.866421

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Simple analytical solutions are presented for the two‐dimensional Stokes’ flow resulting from symmetric arrays of rotlets inside a circular cylinder. From these expressions, streamline patterns are easily drawn which show different varieties of free and attached eddies within the fluid; they bear many comparisons with the recent experiments of Munson and Sturges [Phys. Fluids26, 1173 (1983)].

ISSN:0031-9171    

DOI:10.1063/1.866422

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The stability of Jeffery–Hamel flow in a divergent wedge is considered by means of some initially localized disturbances, whose evolution downstream with time is studied by an integral of fixed frequency modes with respect to the frequency parameter. It is found, typically, that even in regions of parameter space that are nominally ‘‘unstable,’’ the original localized disturbance grows very little before decaying downstream.

ISSN:0031-9171    

DOI:10.1063/1.866423

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The dynamics of two‐dimensional Rayleigh–Be´nard convection rolls are studied in a finite layer with no‐slip, fixed temperature upper and lower boundaries and no‐slip insulating side walls. The dominant mechanism controlling the number of rolls seen in the layer is an instability concentrated near the side walls. This mechanism significantly narrows the band of stable wavenumbers although it can take a time comparable to the long (horizontal) diffusion time scale to operate.

ISSN:0031-9171    

DOI:10.1063/1.866424

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The variational principle derived by Choe and Freidberg [Phys. Fluids29, 1766 (1986)] and used to estimate the geometry of high‐beta tokamak equilibria is extended to include elongation. Ballooning mode stability is then investigated, illustrating the influence of elongation on local and global stability.

ISSN:0031-9171    

DOI:10.1063/1.866425

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The time evolution of the energy for wave propagation in an infinite ideal magnetofluid is studied analytically. It is found that equipartition between the kinetic and potential energies is achieved. Equipartition occurs either in finite time or asymptotically ast→∞ depending upon whether the initial data are compactly supported or have finite energy, respectively.

ISSN:0031-9171    

DOI:10.1063/1.866426

出版商:AIP    

年代:1987

数据来源: AIP