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  • 1
    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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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Characteristics of high-confinement modes in Alcator C Mod (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1992-1998 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The regime of high particle and energy confinement known as the H mode [Phys. Rev. Lett. 49, 1408 (1982)] has been extended to a unique range of operation for divertor tokamaks up to toroidal fields of nearly 8 T, line-averaged electron densities of 3×1020 m−3, and surface power densities of nearly 0.6 MW/m2 in the compact high-field tokamak Alcator C Mod [Phys. Plasmas 1, 1511 (1994)]. H modes are achieved in Alcator C Mod with Ion Cyclotron Resonant Frequency (ICRF) heating and with Ohmic heating alone without boronization of the all molybdenum tiled first wall. Large increases in charge exchange flux are observed during the H mode over the entire range of energies from 2 to 10 keV. There appears to be an upper limit to the midplane neutral pressure, of about 0.08 Pa above which no H modes have been observed. The plasmas with the best energy confinement have the lowest midplane neutral pressures, below 0.01 Pa. There is an edge electron temperature threshold such that Te≥280 eV ±40 eV for sustaining the H mode, which is equal at L–H and H–L transitions. The hysteresis in the threshold power between L–H and H–L transitions is less than 25% on average. Both core and edge particle confinement improve by a factor of 2–4 from L mode to H mode. Energy confinement also improves by up to a factor of 2 over L mode. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871995
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Stabilization of the resistive wall mode by flowing metal walls (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4427-4434 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of flowing metal walls on the resistive wall instabilities is analyzed for a general cylindrically symmetric diffusive pinch configuration. Two types of liquid metal flow are analyzed: a uniform flow which is poloidally symmetric, and a two-stream flow consisting of two opposite streams splitting at the top and merging at the bottom. It is found in both configurations that when the liquid wall flow velocity exceeds a critical value, the resistive wall mode is stabilized. However, for the two-stream flow the critical velocity is several times smaller than that for the uniform flow. Still in a realistic experiment one needs a flow velocity of a few tens m/s to stabilize the resistive wall mode. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1399328
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