Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • 1990-1994  (16)
Source
Material
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Instability of fluid vortices and generation of sheared flow (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2758-2768 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fluid equilibrium consisting of a periodic array of counter-rotating vortices is found to be unstable to the generation of one-dimensional sheared flow along the direction of periodicity. This instability is inviscid (exists for zero viscosity μ) or viscous (with growth rate γ∼μ3/4) depending on the elongation of the vortices. Nonlinearly, the instability goes through a vortex reconnection or "peeling'' phase in which one of the vortices per period is destroyed, leading to a state with a chain of islands. Without a source, the flow evolves to pure one-dimensional shear flow, which decays because of viscosity on a much longer time scale. In the presence of a source driving the initial vortices, the flow evolves to an equilibrium having vortex flow plus shear flow and, for sufficiently high Reynolds number, having only one vortex per periodicity length rather than two, i.e., with islands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860149
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Reply to "Comment on ‘Peeling of convection cells and the generation of sheared flow' [Phys. Fluids B 4, 488 (1992)]'' (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 658-658 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The comments of Montgomery and Matthaeus on the authors' paper1, have been answered. The results do not contradict those of Montgomery and Matthaeus but for simple case considered, transition to shear flow state and shape of initial vortices is explained. (AIP)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860501
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Theory of ion temperature gradient instabilities: Thresholds and transport (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1822-1832 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An investigation of the ion temperature gradient instability that focuses on the behavior of the mode when it is weakly unstable is presented. It is shown that ηi= (2)/(3) is the threshold for long wavelength instability, ηi being the ratio of the density gradient scale length to the ion temperature gradient scale length. For ηi〉0.902, a short wavelength mode is concomitantly unstable. The transport resulting from both the short and the long wavelengths is shown to constitute a "soft'' turn on of anomalous transport for ηi〈2, with long (short) wavelengths dominating for high (weak) enough collisionality. The point ηi=2 represents a "hard'' threshold for transport: Beyond this point, large, collisionless transport over all wavelengths is precipitated. A nonlocal collisional theory as well as a kinetic theory with a Krook collision operator are presented to describe the progression from weak to strong instability. Transport estimates, based on mixing length arguments, are given for the various regimes incorporated by the critical points ηi= (2)/(3) , 0.902, and 2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859454
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Spontaneous and driven perpendicular rotation in tokamaks (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2519-2524 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent theoretical work pertaining to spontaneously generated or forced plasma rotation in tokamaks is discussed. A description of the spontaneous poloidal spin-up of tokamaks from the Stringer effect is given, highlighting the necessary condition of poloidally asymmetric particle accumulation. The possibility of inducing poloidal rotation using the Stringer effect by poloidally asymmetric particle fueling is suggested. The linear theory of E×B velocity shear stabilization of tokamak microinstabilities is discussed with an emphasis on the general features of the theory and some nonlinear concerns. It is argued that the critical velocity shear for stabilization of microinstabilities in tokamaks required by linear theory may be, in order of magnitude, a universal frequency. The feasibility of driving perpendicular rotation in tokamaks by neutral beam injection, to suppress microturbulence, is assessed for both toroidal and poloidal injection schemes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860738
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Three-dimensional fluid simulations of the nonlinear drift-resistive ballooning modes in tokamak edge plasmas (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3712-3727 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three-dimensional study of the turbulence and sheared flow generated by the drift-resistive ballooning modes in tokamak edge plasmas has been completed. The fluid simulations show that 10%–15% percent density fluctuations can develop in the nonlinear state when the self-consistently generated shear flow is suppressed. These modes are also found to give rise to poloidally asymmetric particle transport. Characteristic scale lengths of these fluctuations are isotropic in the plane transverse to B and smaller than the connection length along the field line. Sheared poloidal flow is self-consistently driven by both the Reynolds stress and the Stringer mechanisms. In the presence of self-consistent shear flow, the transverse spectrum is no longer isotropic transverse to B. The vortices become elongated in the poloidal direction. Also, there is a substantial reduction in both the level of fluctuations of the density and potential and the associated particle transport. These features are in qualitative agreement with L–H transitions observed in tokamaks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860842
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Stability of resistive and ideal ballooning modes in the Texas Experimental Tokamak and DIII-D (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1846-1854 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stability of drift resistive ballooning modes is examined using the reduced Braginskii equations, which include electron temperature and magnetic fluctuations. The Texas Experimental Tokamak (TEXT) [Phys. Fluids B 2, 2879 (1990)] edge plasma is found to be unstable for a broad range of mode numbers. For low mode numbers (m〈70), the plasma is unstable to the drift resistive ballooning mode, which has a growth rate that scales linearly with the resistivity (γ∼η). As the mode number increases, a transistion is found to the resistive ballooning mode with the usual scaling of γ∼η1/3. A similar analysis is made for parameters from DIII-D [Phys. Fluids B 2, 1405 (1990)] for both the L mode and the H mode. It is found that the L mode is unstable to the resistive mode, but β ≈ βI/6, where βI is the critical β for the ideal instability. The H mode is weakly unstable to the resistive mode and is only about a factor of 2 below the β threshold for the more robustly unstable ideal mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860038
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    The effect of bandwidth on the convective Raman instability in inhomogeneous plasmas (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2882-2888 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of bandwidth on the convective amplification of the Raman instability in the underdense, inhomogeneous plasma is investigated. For the case when the homogeneous growth rate γ0(very-much-less-than)Δω, where Δω is the bandwidth, it is shown both analytically and numerically that there is no effect of bandwidth on the convective amplification. The reduction in the homogeneous growth rate due to the bandwidth is compensated for by an increase in the interaction region such that the convective amplification is unaffected. For γ0(approximately-greater-than)Δω there is a statistical enhancement in the amplification factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859921
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Transport barrier in ion temperature gradient driven turbulence (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1381-1385 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fluid simulations of long ηi modes are presented that demonstrate that the density profile plays a much more profound role in controlling global energy confinement than would be expected from simple marginal stability considerations. Specifically, local steepening of the density gradient produces an effective transport barrier that allows ion global confinement to improve dramatically. The threshold value ηi =d ln(Ti)/d ln(n) required for instability ηic plays a fundamental role in the formation of the transport barrier—no transport barrier forms for ηic〈1. The implication of these results for understanding ion energy confinement in tokamaks is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859703
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Ion-temperature-gradient-driven turbulence and transport in a sheared magnetic field (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 620-626 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analytical and numerical investigation has been completed of the nonlinear growth and saturation of long-wavelength ion-temperature-gradient-driven turbulence in a sheared magnetic field for the case of an isolated rational surface. The radial correlation length of the turbulence is found to be of order ρiLs/ Lt, with ρi the ion Larmor radius, Ls the magnetic shear length, and LT the temperature scale length. The scaling of the resulting anomalous cross-field diffusivity is χ⊥∝g(ηi)(ρ2i/LTLy) (Ls/LT)2ρivti, where g(ηi) is obtained from the numerical results. In the poloidal direction, the spectrum collapses to the longest wavelength, Ly, available. Explicit results for the function g(ηi) are presented for values of ηi ranging from just above marginal stability ηic to ηi=∞. Although the quasilinear temperature profile is held fixed, the transport rates are very small as a result of local flattening of the temperature profile near the rational surface. The implications of these results for understanding anomalous transport in tokamaks are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859861
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Auxiliary heated detached plasmas in tokamaks (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 324-328 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Earlier studies on Ohmically heated plasmas have been extended to auxiliary heated detached plasmas in tokamaks. Assuming the electron energy loss channel to be the dominant one and caused by ηe modes, the effect of auxiliary power in determining the thermal equilibria of detached plasmas is examined. Specific predictions for central electron temperature, core plasma radius, and electron energy confinement time as a function of the auxiliary power for the tokamak fusion test reactor (TFTR) [J. Nucl. Mater. 145, 186 (1987)] parameters are obtained. Density limit enhancement by auxiliary power is also studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859321
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...