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  • 1
    Electronic Resource
    Electronic Resource
    Toroidal field effects on dipole equilibrium and stability at finite plasma pressure (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1452-1458 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of a toroidal magnetic field on the equilibrium and stability of a plasma confined by the magnetic field of a point dipole is considered, since it may be necessary to introduce a toroidal magnetic field to smooth electron heating or other asymmetries in the toroidal direction that can lead to toroidal electric fields and a loss of confinement due to radial E×B drift. To begin, a toriodal magnetic field is shown to restore confinement by reducing electron heating departures from axisymmetry. Then the Grad–Shafranov equation for a point dipole in the presence of a toroidal field is solved to explicitly demonstrate that an equilibrium exists. Finally, it is shown that a toroidal magnetic field destabilizes the otherwise stable point dipole ballooning modes at high plasma pressure. Consequently, if a toroidal magnetic field is necessary to remove toroidal heating asymmetries in a dipole equilibrium, the heating may have to be performed transiently or at lower plasma pressures. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873964
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  • 2
    Electronic Resource
    Electronic Resource
    Comments on particle and energy balance in the edge plasma of Alcator C-Mod (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 3373-3376 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Particle balance is examined in a large set of representative Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] diverted plasmas using measurements of neutral gas pressures and ionization source strengths in the main chamber, and parallel plasma flow into the divertor. It is inferred that plasma flow in the scrape-off layer (SOL) is dominated by transport to the main chamber walls rather than by flow into the divertor. It follows that (i) the effective diffusion coefficient for anomalous cross-field particle transport in the SOL must rapidly grow with distance from the magnetic separatrix to account for the measured density profiles, (ii) a significant fraction of the power from the core plasma can be convected rather than conducted into the SOL, and (iii) the neutral pressure at the outer midplane is governed more by cross-field plasma transport than by wall–plasma separation or divertor/limiter geometries. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873051
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  • 3
    Electronic Resource
    Electronic Resource
    Plasma recombination and molecular effects in tokamak divertors and divertor simulators : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1638-1646 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analysis of the experimental data from tokamaks and linear divertor simulators leads to the conclusion that plasma recombination is a crucial element of plasma detachment. Different mechanisms of plasma recombination relevant to the experimental conditions of the tokamak scrape-off layer (SOL) and divertor simulators are considered. The physics of Molecular Activated Recombination (MAR) involving vibrationally excited molecular hydrogen are discussed. Although conventional Electron–Ion Recombination (EIR) alone can strongly alter the plasma parameters, MAR impact can be substantial for both tokamak SOL plasma and divertor simulators. Investigation of the effects of EIR on the plasma flow in divertor simulators shows that due to the balances of (a) energy transport and electron cooling, and (b) the plasma flow and recombination, that EIR extinguishes the simulator plasma at an electron temperature about 0.15 eV. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872268
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetic effects in tokamak scrape-off layer plasmas : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1672-1680 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The short mean-free path expansion used in fluid modeling of scrape-off layer plasmas is often violated for typical discharge parameters, especially by the superthermal particles, which carry most of the heat flux. Thus, the tail of the distribution function can strongly depart from Maxwellian due to nonlocal mean-free path effects, which can modify plasma transport, impurity radiation, and plasma–neutral gas interactions. These nonlocal effects become particularly pronounced for detached plasma conditions that are characterized by sharp gradients in the plasma parameters along the magnetic field. These problems are being addressed by developing one spatial dimension and two velocity variables, fully kinetic, collisional, and time-dependent particle-in-cell code, W1 [Contrib. Plasma Phys. 34, 436 (1994)], and its parallel-computer version, PW1 [Contrib. Plasma Phys. 34, 424 (1996)]. Comparisons are made with the Fokker–Planck code ALLA [Phys. Plasmas 3, 1634 (1996)] and with experimental results. Kinetic effects on probe measurement interpretation, impurity radiation, and parallel heat conductivity due to non-Maxwellian features in scrape-off layer plasmas are considered. Heat conductivity is compared with ad hoc heat flux limit models. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872280
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  • 5
    Electronic Resource
    Electronic Resource
    Scaling laws for two-dimensional divertor modeling (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 927-938 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To gain insight into divertor operation, similarity techniques are employed to investigate whether model systems of equations plus boundary conditions admit scaling transformations that lead to useful divertor scaling laws. These can be used to perform similarity experiments or more fully exploit large computer simulations. Fluid plasma models of the divertor region are adopted that ignore anomalous processes. We consider neutral descriptions in both the short and long mean-free path limits. As usual, the more approximations that are made, the more scaling transformations are allowed, leading to fewer independent dimensionless parameters that need to be considered, thereby imposing fewer divertor similarity constraints. The simplest model considered balances electron heat conduction with impurity radiation and places the fewest constraints on similarity. To be able to model the onset of detached divertor operation in short mean-free path regimes, a fluid neutral description is employed that balances plasma pressure by neutral pressure. In this model the constraints on divertor similarity are most severe. A less constrained long mean-free path or Knudsen neutral model is also considered. It models the onset of detached divertor operation by balancing plasma pressure by momentum transfer to the neutrals that are randomized by collisions with the deep slot sidewalls. The simpler models have relaxed divertor similarity constraints, but all models remain severely restricted by the collisionality constraints. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871798
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  • 6
    Electronic Resource
    Electronic Resource
    Radiative instabilities in the tokamak scrape-off layer during edge-localized mode activity (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3769-3776 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to reduce the heat flux entering the divertor, it is desirable to have strong impurity radiation in the scrape-off layer (SOL) of reactor-size tokamaks like the International Thermonuclear Experimental Reactor [International Thermonuclear Experimental Reactor (ITER) Conceptual Design Activity Final Report, ITER Documentation Series No. 16 (International Atomic Energy Agency, Vienna, 1991)]. Under such circumstances, however, the SOL plasma is likely to be unstable to the radiative condensation instability. In the present paper, an investigation is undertaken to study the effects of edge-localized mode (ELM) activity on this instability. In the linear regime, it is demonstrated that high-frequency ("grassy'') ELM's may parametrically excite acoustic waves. The possibility of nonlinear radiative collapse with concomitant stratification of the plasma is discussed, and solutions describing nonlinear traveling waves are derived in which the plasma goes over from equilibrium state to another. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871076
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  • 7
    Electronic Resource
    Electronic Resource
    Plasma rotation and electrostatic potential formation at the edge due to suprathermal particle lossesf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1583-1591 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Generation of the edge radial electric field and corresponding plasma rotation is studied for toroidal confinement systems with a separatrix configuration of magnetic surfaces. It is shown that classical acceleration of plasma by ion orbital losses can explain the electric field and the plasma rotation observed near walls when plasma flow to the neutralizing wall is included.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870710
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  • 8
    Electronic Resource
    Electronic Resource
    Tokamak edge plasma simulation including anomalous cross-field convective transport (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 1287-1299 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Multi-fluid two-dimensional transport models such as the UEDGE code model [T. D. Rognlien et al., J. Nucl. Mater. 196–198, 34 (1992)] are widely used in the simulation of tokamak edge plasmas. Usually these models are based on the assumption of anomalous plasma diffusion in the direction perpendicular to magnetic field lines. As will be shown, the pure diffusive cross-field transport model is inadequate and fails to match properly plasma parameters measured both in the scrape-off layer (SOL) and in the divertor of the DIII-D tokamak. Recently it has been suggested that specific nondiffusive transport occurs in the edge plasma [S. I. Krasheninnikov, Phys. Lett. A 283, 368 (2001)]. The nondiffusive transport is incorporated to the UEDGE model by adding the anomalous cross-field convective velocity for plasma species and by prescribing a specific two-dimensional profile to this velocity. A series of highly radiative discharges obtained on the DIII-D tokamak is analyzed using the UEDGE code with the hybrid, convective and diffusive, cross-field transport model. For these discharges, anomalous convective velocity profiles are adjusted until the simulated radial profiles agree with measurements in the SOL and in the divertor. It is found that in order to reproduce most of the extensive experimental data, anomalous plasma convection should play the dominant role in the outboard edge-plasma region. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1459059
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  • 9
    Electronic Resource
    Electronic Resource
    Plasma equilibria in dipolar magnetic configurations : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1831-1838 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of finite plasma pressure and pressure anisotropy, toroidal rotation and gravity on the equilibrium, flow, and stability of plasma in dipolar magnetic configurations are considered. Dipolar equilibria are of interest for magnetic confinement experiments in the laboratory and understanding the physics of magnetospheric and astrophysical plasmas. It is demonstrated that realistic solutions of the appropriate ideal magnetohydrodynamics (MHD) equations can be found in a separable form which drastically simplifies the equations and even allows us to analytically obtain some limiting forms of the nonlinear solutions. The MHD stability of these equilibria is explicitly evaluated in some cases. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874005
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  • 10
    Electronic Resource
    Electronic Resource
    Ionization-recombination instability and multifaceted asymmetric radiation from the edge in magnetic fusion devices (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 950-956 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent experimental studies of MARFEs (Multifaceted Asymmetric Radiation From the Edge) in the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] and TEXTOR-94 (upgraded Torus Experiment for Technology Oriented Research) [A. M. Messiaen et al., Phys. Plasmas 4, 1690 (1997)] tokamaks reveal low plasma temperature T∼0.7 eV, strong hydrogen radiation, and plasma recombination in the MARFE region. These results contradict a well-accepted model, based on low-Z impurity radiation, and can be better explained by a nonlinear stage of an ionization-recombination instability, discussed recently in the literature. In this paper, a qualitative analysis of the instability is performed, and its growth rate γ and the range of wavelengths of unstable perturbations are estimated. It is found that the instability exists for plasma temperatures near the wall T(approximately-less-than)10 eV; and for lower temperatures, T∼1 eV, volumetric recombination becomes important and can increase γ considerably compared to the case without the volumetric recombination. The results of the qualitative analysis are confirmed by a numerical solution of the linearized fluid equations with recombination and ionization describing MARFEs. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873893
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