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  • 1
    Electronic Resource
    Electronic Resource
    Effect of aspect ratio on magnetic field fluctuations in the reversed-field pinch (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3407-3411 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of aspect ratio on magnetic field fluctuations in reversed-field pinches is investigated using a three-dimensional magnetohydrodynamic code. Configurations with aspect ratios of 1.1, 2.2, and 4.4 are modeled. The results are extrapolated to aspect ratio 8.8 for comparison with the Extrap T1 experiment [Nucl. Fusion 34, 427 (1994)]. It is found that the average modal amplitudes decrease with aspect ratio. However, the spectrum broadens correspondingly, resulting in negligible effect on the magnetic fluctuation level. The computed spectrum dynamics are found to be in good agreement with experimental observations on the T1 experiment. Quantitative evaluations of the field line stochasticity indicate no dependence of the mean magnetic field diffusion rate on aspect ratio. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871122
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  • 2
    Electronic Resource
    Electronic Resource
    The role of m=0 modal components in the reversed-field-pinch dynamo effect in the single fluid magnetohydrodynamics model (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1671-1674 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The role of the m=0 modal components on the reversed-field-pinch (RFP) dynamo effect is examined in the single fluid magnetohydrodynamic (MHD) model by comparing results with and without various nonlinear convolutions of the m=0 spectrum. Results indicate that the dynamo effect comes directly from the m=1 instabilities and the effect of other nonlinear convolutions is small. Scaling studies of δB/B with the Lundquist number (S) are also performed. It is found that δB/B is independent of S (diffusionlike scaling), which is consistent with the view that the dynamo effect arises directly from the m=1 modes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858946
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  • 3
    Electronic Resource
    Electronic Resource
    Numerical simulation of reversed-field pinch rising current operation (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 3023-3026 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One of the most interesting reversed-field pinch (RFP) experimental results occurs in discharges where the toroidal current is slowly raised after toroidal field reversal is established. These discharges exhibit the RFP dynamo effect in its most unambiguous form showing the strong nonlinear coupling of the external poloidal and toroidal magnetic field circuits via the plasma-magnetic-field configuration. Three-dimensional, single-fluid resistive magnetohydrodynamic simulations of these discharges are reported. It is found that the appropriate nonlinear coupling needed to explain the experimental observations is provided by one or more helical resistive modes of long wavelength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865462
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  • 4
    Electronic Resource
    Electronic Resource
    Compressibility as a feature of field reversal maintenance in the reversed-field pinch (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 898-902 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Five different codes have been used to simulate the identical problem in reversed-field pinch (RFP) dynamics using the resistive magnetohydrodynamic (MHD) model in three dimensions with the same set of initial and boundary conditions. Three codes are compressible, while two are incompressible. The assumption of incompressibility was made in the spirit of reducing the model so that, for example, the codes would run faster while retaining the relevant physics. The results show that the three compressible codes agree quite well with each other and the two incompressible codes agree with each other also, but the compressible and incompressible models show qualitatively different behavior. Most importantly, for a certain set of boundary and initial conditions, the compressible codes predict field reversal maintenance while the incompressible codes do not. Thus compressibility is an important feature of RFP physics. This is in contrast to tokamak physics where the strong toroidal field enforces incompressibility at low poloidal beta.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865060
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  • 5
    Electronic Resource
    Electronic Resource
    Suppression of m=2 islands by electron cyclotron heating in the Texas Experimental Tokamak: Experiment and theory (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3239-3245 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron cyclotron heating (ECH) is used to suppress m=2 magnetohydrodynamic (MHD) oscillations in the Texas Experimental Tokamak (TEXT) [Nucl. Technol. Fusion 1, 479 (1981)]. The location of ECH power deposition is controlled by a movable antenna. The MHD activity is suppressed when the ECH beam is directed close to the q=2 surface. The experiment is simulated using a three-dimensional resistive MHD code in cylindrical geometry. For fixed plasma current, the saturated m=2 island width is found to depend on the value of the safety factor at the magnetic axis (q0). The simulation suggests that the observed saturated m=2 island in the pre-ECH plasma, which typically occupies 25% of the minor radius, corresponds to q0∼1.3. The suppression of the island in the presence of ECH is attributed to current profile modification. In some discharges, the m=2 activity does not resume even after the ECH pulse is turned off.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860659
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  • 6
    Electronic Resource
    Electronic Resource
    Simulation of oscillating field current drive on the reversed-field pinch (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 1979-1987 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Oscillating field current drive on the reversed-field pinch is simulated by using a three-dimensional nonlinear resistive magnetohydrodynamic model in conjunction with a one-dimensional hyper-resistive model. When input from the three-dimensional model is used for fluctuating fields in the hyper-resistive equations, the two models are found to give similar relaxed profiles. Comparisons are made with experiments on the Los Alamos National Laboratory ZT-40M reversed-field pinch device [Nucl. Fusion 25, 1321 (1985)]. Simulation results indicate that the oscillation period must be much less than the resistive decay time, but should not be much less than the hyper-resistive relaxation time, in order to maintain reversal without a steady-state driving field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866645
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  • 7
    Electronic Resource
    Electronic Resource
    Three-dimensional magnetohydrodynamic studies of the reversed-field pinch (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 321-333 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three-dimensional computational studies of nonlinear resistive megnetohydrodynamic (MHD) instabilities in the reversed-field pinch are presented. It is found that multihelicity mode coupling effects alter the evolution of m=1 modes from that obtained in single helicity. Strong mode coupling to m=0 and m=2 is observed. Magnetic island overlap results in stochastic field lines. At low values of the pinch parameter this is confined to the central region of the pinch; for larger values the stochasticity may extend to the wall. Healing of outer flux surfaces is observed as modes peak and relax. Decay of positive toroidal flux is retarded. Impact on confinement is discussed, and connection is made with experimental observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865151
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  • 8
    Electronic Resource
    Electronic Resource
    The thermal stability of coronal loops numerical simulations (1991)
    Springer
    Solar physics 132 (1991), S. 95-108 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the radiative stability of thermally isolated coronal loops with free-flow boundary conditions by nonlinear numerical simulation. We first establish a chromosphere-to-corona loop equilibrium (including the option of a deep chromosphere) by following the nonlinear evolution from an initial isothermal state with rigid boundaries. We then change the end conditions, to allow free flow and to fix the temperature, and investigate the response to non-isobaric perturbations. Within a family of loops of the same pressure, we find long hot loops to be stable and short cool loops to be unstable to the thermal chromosphericexpansion mode. The stable cases remain so, even when long chromospheric ends and/or gravity are added. In those cases which are unstable, we follow the subsequent nonlinear evolution which exhibits swelling of the chromosphere until the entire loop becomes cool and dense.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00159132
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