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  • 1
    Electronic Resource
    Electronic Resource
    Detailed comparison of simulated and measured plasma profiles in the scrape-off layer and edge plasma of DIII-D (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3663-3680 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The results of detailed comparisons between experimental measurements of the scrape-off layer and divertor plasmas and simulations using the UEDGE code for a DIII-D discharge [J. Luxon et al., Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1986), Vol. I, p. 159] are reported. The simulations focus on understanding the flow of both fuel and impurity particles throughout the edge and scrape-off layer (SOL) plasma. The core impurity content and the core hydrogen ionization rate can be explained by sputtering and recycling in the divertor region alone. The model reproduces most of the detailed experimental measurements. The simulations include the effect of intrinsic impurities, assumed to be carbon originating from sputtering of the plasma facing surfaces. The simulations accurately reproduce the total radiated power, although the spatial profile of radiation is somewhat narrower in the simulation. The measured carbon density on closed field lines is reproduced well with the simulation. Comparison of carbon emission lines indicates the total carbon sputtering yield is a factor of 2 to 4 less than expected, although the total radiated power and core carbon content are insensitive to the sputtering yield. The agreement between simulation and experiment permits more meaningful interpretation of the experimental measurements. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1286509
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  • 2
    Electronic Resource
    Electronic Resource
    Low-to-high confinement transition simulations in divertor geometry (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1951-1958 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent results are presented for turbulence in tokamak boundary plasmas and its relationship to the low-to-high confinement (L–H) transition in a realistic divertor geometry. These results are obtained from a three-dimensional (3D) nonlocal electromagnetic turbulence code, which models the boundary plasma using fluid equations for plasma vorticity, density, electron and ion temperatures and parallel momenta. With sources added in the core-edge region and sinks in the scrape-off layer (SOL), the code follows the self-consistent profile evolution together with turbulence. Under DIII-D [Luxon et al., International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1986), p. 159] tokamak L-mode conditions, the dominant source of turbulence is pressure-gradient-driven resistive X-point modes. These modes are electromagnetic and curvature-driven at the outside mid-plane region but become electrostatic near X-points due to magnetic shear and collisionality. Classical resistive ballooning modes at high toroidal mode number, n, coexist with these modes but are sub-dominant. Results indicate that, as the power is increased, these modes are stabilized by increased turbulence-generated velocity shear, resulting in an abrupt suppression of high-n turbulence and the formation of a pedestal in density and temperature, as is characteristic of the H-mode transition. The sensitivity of the boundary turbulence to the direction of the toroidal field Bt is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874044
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  • 3
    Electronic Resource
    Electronic Resource
    Analytic model of power deposition in inductively coupled plasma sources (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1446-1458 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple analytic model valid for all collisionality regimes is developed to describe the power deposition in a cylindrical inductively coupled plasma source with a planar coil. The heating is ohmic at high pressures and remains finite at low pressures. The low-pressure collisionless heating is due to kinetic nonlocal effects. The model is in good agreement with other calculations of collisionless heating. A diffusion model is then used to determine the plasma density profile and the electron temperature in terms of the gas pressure and the source geometry. The heating and diffusion models are used to determine the scaling of the inductive electric field with applied frequency and input power, and the results are compared with published experimental data to verify the scaling. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360723
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  • 4
    Electronic Resource
    Electronic Resource
    Simulation of experimentally achieved DIII-D detached plasmas using the UEDGE code (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1967-1975 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The introduction of a divertor Thomson scattering system in DIII-D [J. Luxon et al., International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1986), p. 159] has enabled accurate determination of the plasma properties in the divertor region. Two plasma regimes are identified: detached and attached. The electron temperature in the detached regime is about 2 eV, much lower than 5–10 eV determined earlier. Fluid models of the DIII-D scrape-off layer plasma successfully reproduce many of the features of these two regimes, including the boundaries for transition between them. Detailed comparison between the results obtained from the fluid models and experiment suggest the models underestimate the spatial extent of the low-temperature region associated with the detached plasma mode. Low-temperature atomic physics processes that are not included in the present models may account for this discrepancy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871993
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  • 5
    Electronic Resource
    Electronic Resource
    Two-dimensional electric fields and drifts near the magnetic separatrix in divertor tokamaks : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1851-1857 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-dimensional calculation is presented for the transport of plasma in the edge region of a divertor tokamak solving continuity, momentum, and energy balance fluid equations. The model uses classical processes of parallel transport along the magnetic field and cross-field drifts together with anomalous radial diffusion, including perpendicular ion viscosity. The self-consistent electrostatic potential is calculated on both sides of the magnetic separatrix via quasineutrality and current continuity. Outside the separatrix, the model extends to material divertor plates where the incident plasma is recycled as neutral gas and where the plate sheath and parallel currents dominate the potential structure. Inside the separatrix, various radial current terms—from anomalous viscosity, collisional damping, inertia, and ∇B drifts—contribute to determining the potential. The model rigorously enforces cancellation of gyroviscous and magnetization terms from the transport equations. The results emphasize the importance of E×B particle flow under the X-point which depends on the sign of the toroidal magnetic field. Radial electric field profiles at the outer midplane show strong variation with the magnitude of the anomalous diffusion coefficients and the core toroidal rotation velocity, indicating that shear stabilization of edge turbulence can likewise be sensitive to these parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873488
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  • 6
    Electronic Resource
    Electronic Resource
    Kinetic effects on particle and heat fluxes in detached plasmas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3386-3396 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model of high recycling scrape-off layer plasmas in tokamaks is presented where both ion and electron species are described by nonlinear kinetic equations. Coulomb and charged-neutral particle collisions are included. The ambipolar electric field and electrostatic sheath potential are evaluated self-consistently. Two models of fluid neutral transport are used to distinguish the neutral density variation for different tokamak divertor geometries. These models are incorporated into a comprehensive three-dimensional (1-D, 2 V) hybrid collisional particle-in-cell–Monte Carlo code W1 [Contrib. Plasma Phys. 34, 436 (1994)]. This code is used to investigate the effects of neutrals on divertor plasma detachment phenomena and on parallel heat and particle fluxes in the presence of strong gradients where fluid descriptions break down. Results are given for simulations of detached and attached divertor plasmas, and comparisons are made with solutions from a one-dimensional fluid model and with experimental observations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871615
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    E×B circulation at the tokamak divertor X point : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2118-2124 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed measurements in two dimensions by probes and Thomson scattering reveal unexpected local electric potential and electron pressure (pe) maxima near the divertor X point in L-mode plasmas in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)]. The potential drives E×B circulation about the X point, thereby exchanging plasma between closed and open magnetic surfaces at rates that can be comparable to the total cross-separatrix transport. The potential is consistent with the classical parallel Ohm's law. A simple model is proposed to explain the pressure and potential hills in low power, nearly detached plasmas. Recent two-dimensional edge transport modeling with plasma drifts also shows X-point pressure and potential hills but by a different mechanism. These experimental and theoretical results demonstrate that low power tokamak plasmas can be far from poloidal uniformity in a boundary layer just inside the separatrix. Additional data, although preliminary and incomplete, suggest that E×B circulation across the separatrix might be a common feature of low confinement behavior. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1352597
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  • 9
    Electronic Resource
    Electronic Resource
    Electron cyclotron resonance heating in tandem-mirror end cells (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 338-352 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A relativistic Fokker–Planck code is used to study the formation of non-Maxwellian electron velocity distributions in the end cell of a tandem mirror from the combined effects of Coulomb collisions and electron cyclotron radio-frequency (rf) heating. Axial electrostatic potential profiles consistent with thermal-barrier operation are assumed which lead to reasonable electron density profiles. The presence of the potentials results in four populations of electrons occupying different regions of phase space, three of which are solved for self-consistently; the fourth is the passing electron distribution from the center cell that is fixed as a Maxwellian. It is found that the second-harmonic barrier rf near the bottom of the magnetic well, together with rf cavity fields, give a good correspondence to the behavior of the hot electrons in the TMX-U experiment [IEEE Trans. Plasma Sci. PS-16, 1 (1988)]. The behavior of the fundamental rf in the plug region part way up the magnetic well shows poor correlation with experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859323
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  • 10
    Electronic Resource
    Electronic Resource
    Impurity transport in edge plasmas with application to liquid walls : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2120-2126 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transport of impurity ions in a magnetically confined plasma is studied in the region between their origin at a material surface and the core plasma as defined by closed magnetic flux surfaces. The focus is physics understanding of the results of two-dimensional (2-D) transport modeling of the plasma and neutrals. A simple one-dimensional model is introduced to identify key processes and illustrate how such processes affect the core-edge impurity level. The 2-D simulation gives detailed results of scaling of the impurity level with parameters such as anomalous radial diffusion, hydrogen–plasma recycling, core power flux, and core-edge density. The results are obtained for a slab model of a tokamak, but by changing the magnetic connection length, scaling to other types of devices can be inferred. Lithium and fluorine impurities are considered explicitly as examples with low and moderate charge-state number, Z, for liquid wall materials; trends found for these cases provide guidance to the behavior of other impurities. The tolerable amount of impurity influx can be closely associated with the partial thermal collapse of the edge plasma. The results are used to provide a physics picture of previous results on the acceptable evaporative impurity flux from different types of liquid wall materials, and to show how these results can be expected to scale with parameters. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1461384
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