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  • 1
    Electronic Resource
    Electronic Resource
    Neutrals' effects on stability (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3239-3246 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The physics of the neutral atoms is incorporated into a generalized description of edge instabilities in tokamaks and plasmas with a small neutral fraction. The description includes ideal and resistive ballooning modes; modes driven by a radial electron temperature gradient when the plasma is in contact with conducting material surfaces such as limitors or divertor target plates, the destabilizing effect of the parallel variation in the E×B drift frequency, and effects due to the flow of the neutral gas. The analysis considers the neutral dynamics in both the short and long neutral mean-free path limits (relative to the wavelength of the instability), since the perturbed ion–neutral coupling depends on collisionality. Moreover, parallel and cross-field variations in the equilibrium temperatures, densities, and potential are retained as well as the corresponding diamagnetic effects. In the short neutral mean-free path limit, the ion and neutral viscosities and heat fluxes must be retained, while in the long neutral mean-free path limit the neutrals are not perturbed, but the ion viscosity and heat flux must still be considered. The possible destabilizing impact of the new heat flux and viscous terms on stability is demonstrated. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873564
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  • 2
    Electronic Resource
    Electronic Resource
    Ballooning stability of a point dipole equilibrium (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2526-2529 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The energy principle is employed to show that the equilibrium confined by the magnetic field of a point dipole is stable to ballooning modes. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874092
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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    On the sink/source effects in two-dimensional plasma turbulence (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 5091-5095 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ad hoc sinks and sources of turbulence are added in the two-dimensional (2D) magnetized plasma model to mimic excitation and damping of the modes. Depending on linear growth and damping rates and sink and source localizations, two kind of the turbulence and large scale flows evolution regimes were found: quasisteady state and dynamic. The quasisteady states with saturated averaged energy and enstrophy are characterized by strong large scale flows generated due to the inverse cascade in the nonlinear mode coupling. It is shown that for the adopted model there is not complete stabilization of high-k harmonics (microturbulence) by the generated zonal flows and convective cells. The dynamic regimes are characterized by nonvanishing energy and enstrophy fluctuations around averaged values and the energy spectrum has maximum, which corresponds to the turbulence source. The inverse cascades in these regimes are suppressed by the mode damping in the k-space sink region. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415750
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  • 7
    Electronic Resource
    Electronic Resource
    Modeling of particle and energy transport in the edge plasma of Alcator C-Mod (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2791-2796 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the present study recycling and transport in the edge plasma of Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] is modeled and analyzed with the multi-fluid code UEDGE [T. D. Rognlien et al., J. Nucl. Mater. 196–198, 347 (1992)]. Matching the experimental plasma density profiles in the scrape-off layer (SOL) requires a spatially dependent effective anomalous diffusion coefficient D⊥ growing rapidly towards the wall. The midplane pressure of neutral gas, Pmid, is a key parameter that reflects the magnitude of anomalous transport of plasma from the core. Recycling of plasma on the main chamber wall appears to be quite significant, especially in the case of high Pmid∼0.3 mTorr when the main wall provides ∼70% of recycling neutrals in the main chamber. In the upper SOL (well above the x point) draining of particles by the poloidal flow is weak and thus the particle balance is predominantly radial. For the radial heat transport it is found that energy flux carried by radial plasma convection and by charge-exchange (CX) neutrals is quite significant in SOL. In the high Pmid case, heat conduction by CX neutrals along with radial heat convection by plasma carries most of the power flux (∼75%) across the last closed flux surface. Even in the low Pmid case, heat conduction by CX neutrals dominates the radial heat flux far out in the SOL. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873236
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  • 8
    Electronic Resource
    Electronic Resource
    Volume recombination and opacity in Alcator C-Mod divertor plasmas : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1759-1766 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Volume recombination within the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] divertor plasma is measured and found to be a significant fraction of the total ion sink under detached divertor conditions. The recombination occurs in regions where Te∼1 eV and ne∼1021 m−3. Measurements of the spatial distribution of the recombination are presented. The determinations of the recombination rates are made by measuring the D0 Balmer spectrum and by using a collisional radiative model describing the level populations, ionization, and recombination of D0. The concept of "recombinations per Balmer series photon" is developed to simplify the determinations. Measurements of the opacity of Lyβ emission are presented. It is observed that up to 50% of the Lyβ emission is trapped, indicating that Lyα is strongly trapped in some cases. The effects of Lyα,β trapping on the "recombinations per photon" curves are calculated and considered in the recombination rate determinations. Observations indicating the presence of molecular activated recombination are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872845
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  • 9
    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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  • 10
    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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