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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Scaling and transport analysis of divertor conditions on the Alcator C-Mod tokamak (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2242-2248 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed measurements and transport analysis of divertor conditions in Alcator C-Mod [Phys. Plasmas 1, 1511 (1994)] are presented for a range of line-averaged densities, 0.7〈n¯e〈2.2×1020 m−3. Three parallel heat transport regimes are evident in the scrape-off layer: sheath-limited conduction, high-recycling divertor, and detached divertor, which can coexist in the same discharge. Local cross-field pressure gradients are found to scale simply with a local electron temperature. This scaling is consistent with classical electron parallel conduction being balanced by anomalous cross-field transport (χ⊥∼0.2 m2 s−1) proportional to the local pressure gradient. A 60%–80% of divertor power is radiated in attached discharges, approaching 100% in detached discharges. Detachment occurs when the heat flux to the plate is low and the plasma pressure is high (Te∼5 eV). High neutral pressures in the divertor are nearly always present (1–20 mTorr), sufficient to remove parallel momentum via ion–neutral collisions. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871248
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  • 3
    Electronic Resource
    Electronic Resource
    Transport experiments in Alcator-C-Mod (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2308-2313 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of transport experiments has been carried out in Alcator-C-Mod. [Phys Plasmas 1, 1511 (1994)]. Data from both Ohmic and ICRF (ion cyclotron range of frequencies) heated plasmas can be fitted with an L-mode (low mode) scaling law. The Ohmic τE's show no scaling with density in any regime and can reach values of 2–3 times neo-Alcator. Impurity confinement has been studied with the laser blow-off technique with τI showing nearly linear scaling with plasma current. Ohmic and ICRF H modes are obtained over a wide range of discharge parameters, extending the range in the international database for nB, by almost a factor of 10. The power threshold for ELM-free (edge localized mode) discharges is in rough agreement with the scaling P/S=0.044nB. Energy diffusivities of Ohmic and ICRF heated plasmas have been measured from local analysis of plasma profiles and power fluxes. The same analysis produces a value for plasma resistivity which lies between the Spitzer and neoclassical calculations. Analysis of plasma transients have yielded values for particle diffusivity and convection velocity. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871254
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  • 4
    Electronic Resource
    Electronic Resource
    Comparison of detached and radiative divertor operation in Alcator C-Mod (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1908-1915 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The divertor of the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511 (1994)] routinely radiates a large fraction of the power entering the scrape-off layer. This dissipative divertor operation occurs whether the divertor is detached or not, and large volumetric radiative emissivities, up to 60 MW m−3 in ion cyclotron range of frequency (ICRF) heated discharges, have been measured using bolometer arrays. An analysis of both Ohmic and ICRF-heated discharges has demonstrated some of the relative merits of detached divertor operation versus high-recycling divertor operation. An advantage of detached divertor operation is that the power flux to the divertor plates is decreased even further than its already low value. Some disadvantages are that volumetric losses outside the separatrix in the divertor region are decreased, the neutral compression ratio is decreased, and the penetration efficiency of impurities increases. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871986
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  • 5
    Electronic Resource
    Electronic Resource
    In situ neutral pressure measurements in a compact high-field tokamak, Alcator C-Mod : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 360-362 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Alcator C-Mod advanced divertor program requires fast in situ, absolutely calibrated neutral pressure measurements. The concept of a linear-geometry ionization gauge, first implemented at Princeton and Garching, was further developed at the MIT Plasma Fusion Center, to meet Alcator C-Mod requirements (high field, compact design). In order to correctly interpret experimental data, the gauge was subjected to a series of in situ calibration tests. It has been found that the gauge sensitivity increases with increasing parallel (to gauge axis) magnetic field. In the high-pressure, high-field limit the basic assumption of the operation of ionization gauges, Ii/Ie(very-much-less-than)1, no longer holds. Consequently a modified expression for the gauge sensitivity, which is a strong function of the primary electron current, is necessary to linearize gauge response over a broad pressure range. Representative pressure measurements from the Alcator C-Mod divertor are included. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146411
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