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  • 1
    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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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Status of the neutron diagnostic experiment for Alcator C-Mod : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4530-4532 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Alcator C-Mod experiment is expected to produce neutrons at a rate of up to 1 × 1016 n/s during its highest performance operation. The global neutron detection system must provide accurate measurement of this production over the full operating regime of the experiment, 1011–1016 n/s. This is accomplished using a series of uranium fission detectors enriched in U235 of staggered sensitivity. These are distributed in two moderator assemblies. A BF3 detector is added to each moderator to cover the lowest operational range. Preliminary calibration of the system has been accomplished using a 65.4 μg Cf252 source placed inside the Alcator C-Mod vacuum vessel. The system design and calibration is discussed herein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143711
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  • 4
    Electronic Resource
    Electronic Resource
    Neutral particle diagnostics for ALCATOR C-Mod : Eighth topical conference on high−temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3119-3121 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The ALCATOR C-Mod experiment will be equipped with two PPPL charge exchange neutral particle analyzers (CENAs), one of which views the plasma tangentially (Rtan/R0=1.05), whereas the second has a horizontally scannable sight line (0≤Rtan/R0≤0.51). The perpendicularly viewing CENA will be capable of analyzing neutrals up to 600 keV amu for up to three separate species simultaneously. Thus high-energy tails can be observed together with the bulk ion temperature. The operation of both analyzers will allow simultaneous measurements from both the perpendicular and tangential chords. The CENAs will be used to study the effect of ICRF heating on the ion energy distribution with emphasis on the high-energy tail. A Fokker–Planck code (FPPRF) [Hammett, Ph.D. thesis, Princeton (1986)] is used to assess the appropriate operating regime of the analyzer (n≤4×1020 m−3 for Ti=2 keV, for Maxwellian ion energy distribution). The experimental design and computer simulations will be detailed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141700
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  • 5
    Electronic Resource
    Electronic Resource
    Density measurements in the edge, divertor and X-point regions of Alcator C-Mod from Balmer series emission (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4246-4251 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron density in the edge, divertor and X-point regions of Alcator C-Mod [Proceedings of the IEEE 13th Symposium on Fusion Engineering (Institute of Electrical and Electronic Engineers, New York, 1990), Vol. 1, p. 13] has been measured using the Stark broadening of high-n (n=8 through 11) transitions of the Balmer series of deuterium. These measurements have been made during typical single null, diverted operation and during gas-puffing through capillaries located within the first wall and divertor. Electron densities up to 1.6×1021 m−3 have been measured in the X-point region and slightly lower densities (5−7×1020 m−3) have been measured in the divertor and edge regions. These results are factors of 2 to 5 larger than the density measurements from the CO2 laser interferometer system in the main chamber (3×1020 m−3) and comparable with probe measurements in the divertor. The ratios of the widths of adjacent lines within the Balmer series have been compared with ratios calculated for the Stark broadening of these lines. These transitions can be used to measure electron densities from 3×1019 to 2×1021 m−3 with a modest resolution spectrograph [(Δλinst=1 A(ring) full width at half maximum)]. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871049
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    The visible, imaging diode arrays on 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. 555-557 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A set of multichord, absolutely calibrated viewing arrays has been used to measure the distributions of H/D and C+2 emissions. A total of 227 chordal views are available, with the chords separated at the plasma by ∼1 cm typically. The chord brightness profiles have been combined and inverted (without recourse to symmetry assumptions) to yield local volume emission rates. Because of the thickness of the superstructure surrounding Alcator C-Mod, the views are from points re-entrant to the vacuum vessel. All but one of the arrays employ 64-channel, linear diode arrays, which are read out serially, thus requiring only one digitizer channel per array. Variable frame rates (∼1 Hz to ∼3.5 kHz) result in an extremely large dynamic range for these detectors. A 35-channel diode array which is read out in parallel and can track fast events like ELMs or pellets is also in use. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146349
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  • 8
    Electronic Resource
    Electronic Resource
    Determination of Hα emissivities from line integrated brightness measurements on 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. 619-621 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Alcator C-Mod is equipped with a 227 chord visible light imaging system. Using a nonlinearly constrained least-squares algorithm, local emissivities have been obtained from the chordal brightness measurements without any assumptions about poloidal symmetry. The robustness of the inversion to noise and calibration errors as well as the spatial information (∼5-cm resolution) obtainable has been examined in detail. Some examples, demonstrating how results from the tomographic reconstruction of the Hα light can be used to calculate a particle confinement time and neutral density are given. Different interference filters in front of the arrays allow the same technique to be applied to other atomic species. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146305
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  • 9
    Electronic Resource
    Electronic Resource
    Creation of a monoenergetic pulsed positron beam (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 1944-1946 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a versatile, pulsed source of cold (ΔE=0.018 eV), low-energy positrons (E(approximate)0–9 eV). Multiple pulses of 105 positrons, each 10 μs in duration, are extracted from a thermalized, room temperature positron plasma stored in a Penning trap. The frequency, duration, and amplitude of the pulses can be varied over a wide range. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118787
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  • 10
    Electronic Resource
    Electronic Resource
    Charged fusion product diagnostics in Alcator C-Mod : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4533-4535 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: With a plasma current of up to 3 MA, toroidal field of up to 9 T, the confinement of the charged fusion products (CFPs) in Alcator C-Mod is expected to be excellent. For example, at maximum current and field, classical losses of the 0.8 MeV 3He, 1 MeV triton, 3 MeV proton, 3.5 and 3.7 MeV alphas are expected to be less than 5%. For the study of the global confinement of CFPs, we plan to measure the burnup of the 1 MeV triton (from the D–D reaction) using a proton recoil detector (NE-213) for the detection of the 14 MeV neutron resulting from the secondary fusion reaction (D–T). On the other hand, loss measurements of CFPs will be made inside the first wall with two detectors (one at the bottom, one at the midplane) using silicon based detectors. The midplane detector will be used to diagnose D–3He plasmas by looking at the unconfined 14.7 MeV proton. In addition to the derivation of fusion yield, energy distribution of the escaping protons will provide information about the ion velocity distribution of the reactants. The bottom detector is time, pitch angle and energy resolved, and thus will be used to study loss mechanisms such as first orbit, toroidal field ripple and magnetohydrodynamics-induced diffusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143813
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