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  • 1
    Electronic Resource
    Electronic Resource
    γ-ray diagnostic for the CIT (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1721-1722 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have examined the feasibility of a fusion γ-ray diagnostic for the Compact Ignition Tokamak (CIT), which is expected to produce 1020 (d, t) fusion reactions per second. Gamma rays at 16.7 MeV are produced by the t(d, γ)He5 fusion reaction. A Monte Carlo coupled neutron–photon transport code is used to model the expected γ-ray spectrum incident upon a Compton spectrometer backed by a Cerenkov detector. The results indicate that a signal of ∼3×104 counts/s and a signal-to-noise ratio of ∼30 can be achieved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140145
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  • 2
    Electronic Resource
    Electronic Resource
    Mode conversion electron heating in Alcator C-Mod: Theory and experiment : 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. 1886-1893 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Localized electron heating [full width at half maximum of Δ(r/a)(approximate)0.2] by mode converted ion Bernstein waves (IBW) has been observed in the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. These experiments were performed in D(3He) plasmas at high magnetic field (B0=7.9 T), high-plasma density (ne0≥1.5×1020 m−3), and for 0.05≤nHe-3/ne≤0.30. Electron heating profiles of the mode converted IBW were measured using a break in slope analysis of the electron temperature versus time in the presence of rf (radio frequency) modulation. The peak position of electron heating was found to be well-correlated with 3He concentration, in agreement with the predictions of cold plasma theory. Recently, a toroidal full-wave ion cyclotron range of frequencies (ICRF) code TORIC [M. Brambilla, Nucl. Fusion 38, 1805 (1998)] was modified to include the effects of IBW electron Landau damping at (k⊥ρi)2(very-much-greater-than)1, This model was used in combination with a 1D (one-dimensional) integral wave equation code METS [D. N. Smithe et al., Radio Frequency Power in Plasmas, AIP Conf. Proc. 403 (1997), p. 367] to analyze these experiments. Model predictions were found to be in qualitative and in some instances quantitative agreement with experimental measurements. A model for mode conversion current drive (MCCD) has also been developed which combines a toroidal full wave code with an adjoint evaluation of the ICRF current drive efficiency. Predictions for off-axis MCCD in C-Mod have been made using this model and will be described. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874012
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  • 3
    Electronic Resource
    Electronic Resource
    Electron heating via mode converted ion Bernstein waves in the Alcator C-Mod tokamak : 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. 1774-1782 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Highly localized direct electron heating [full width at half-maximum (FWHM)≅0.2a] via mode converted ion Bernstein waves has been observed in the Alcator C-Mod Tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. Electron heating at or near the plasma center (r/a≥0.3) has been observed in H(3He) discharges at B0=(6.0–6.5) T and ne(0)≅1.8×1020 m−3. [Here, the minority ion species is indicated parenthetically.] Off-axis heating (r/a≥0.5) has also been observed in D(3He) plasmas at B0=7.9 T. The concentration of 3He in these experiments was in the range of n3He/ne≅(0.2–0.3) and the locations of the mode conversion layer and electron heating peak could be controlled by changing the 3He concentration or toroidal magnetic field (B0). The electron heating profiles were deduced using a rf modulation technique. Detailed comparisons with one-dimensional and toroidal full-wave models in the ion cyclotron range of frequencies have been carried out. One-dimensional full-wave code predictions were found to be in qualitative agreement with the experimental results. Toroidal full-wave calculations indicated the importance of volumetric and wave focusing effects in the interpretation of the experimental results. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872344
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  • 4
    Electronic Resource
    Electronic Resource
    Internal transport barriers on Alcator C-Mod : 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. 2023-2028 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of internal transport barriers (ITBs) has been observed in the core region of Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] under a variety of conditions. The improvement in core confinement following pellet injection (pellet enhanced performance or PEP mode) has been well documented on Alcator C-Mod in the past. Recently three new ITB phenomena have been observed which require no externally applied particle or momentum input. Short lived ITBs form spontaneously following the high confinement to low confinement mode transition and are characterized by a large increase in the global neutron production (enhanced neutron or EN modes). Experiments with ion cyclotron range of frequencies power injection to the plasma off-axis on the high field side results in the central density rising abruptly and becoming peaked. The ITB formed at this time lasts for ten energy confinement times. The central toroidal rotation velocity decreases and changes sign as the density rises. Similar spontaneous ITBs have been observed in ohmically heated H-mode plasmas. All of these ITB events have strongly peaked density profiles with a minimum in the density scale length occurring near r/a=0.5 and have improved confinement parameters in the core region of the plasma. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1345883
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of parametric instabilities in the lower-hybrid range of frequencies in the high-density tokamak (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 983-994 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Parametric decay processes have been studied using rf probes and CO2 laser scattering during the lower-hybrid wave heating and current drive experiments in the Alcator C tokamak. The most important process is believed to be the nonresonant decay into ion-cyclotron quasimodes and/or that into electron-Landau quasimodes. At lower densities ω0/ωlh(0)〉2 [where ω0 is the frequency of the injected pump wave and ωlh(0) is the lower-hybrid frequency evaluated at the plasma center], where efficient current drive and electron heating are obtained, parametric decay is absent or very weak. At higher densities [ω0/ωlh(0) (approximately-less-than)2] strong parametric decay is observed which correlates well with ion tail formation near the plasma edge. Above these densities the electron tail is no longer formed and no significant heating or current drive have been obtained. Parametric decay may be responsible, at least partially, for loss of wave power near the plasma periphery.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865070
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  • 6
    Electronic Resource
    Electronic Resource
    Fast-wave ion cyclotron resonance heating experiments on the Alcator C tokamak (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1657-1670 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper, minority regime fast-wave ICRF (Ion cyclotron range of frequency) heating experiments conducted on the Alcator C tokamak [Nucl. Fusion 26, 1665 (1986)] are described. Up to 450 kW of rf (radio frequency) power at frequency f=180 MHz was injected into plasmas composed of deuterium majority and hydrogen minority ion species at magnetic fields of B0(approximately-equal-to)12 T, densities 0.8≤n¯e≤5×1020 m−3, and minority concentrations 0.25(approximately-less-than)ηH≤8%. Typical ion temperatures were TD(0)∼1 keV, while, depending on density, typical electron temperatures were in the range Te(0)∼1.5–2.5 keV. Central deuterium ion temperature increases of ΔTD(0)=400 eV were observed at n¯e=1×1020 m−3, while significantly smaller ion temperature increases were observed at higher densities. At the highest densities, ion heating became insignificant due in part to a limitation on power handling by the antenna that became more severe with increasing density. Significant electron heating was not observed at any density. Heating of the minority species at low densities indicated severe losses, but at higher densities it was consistent with efficient collisional coupling of the rf power from the hydrogen minority species to the deuterium majority species. Analysis of the deuterium power balance indicated no significant change in the deuterium thermal transport properties as a function of rf power. This may be consistent with the fact that the rf power never exceeded the Ohmic heating (OH) contribution. However, a very strong dependence of the deuterium transport properties on density was observed, and appears to be the dominant process limiting the effectiveness of ICRF heating at high density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859686
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  • 7
    Electronic Resource
    Electronic Resource
    Double transport barrier experiments on Alcator C-Mod : 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. 2149-2155 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Double transport barrier modes (simultaneous core and edge transport barrier) have been observed with off-axis ion cyclotron range of frequencies (ICRF) heating in the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. An internal transport barrier (ITB) is routinely produced in enhanced DαH-mode (EDA) discharges where the minority ion cyclotron resonance layer is at r/a∼|0.5| during the current flat top phase of the discharge. The density profile becomes peaked without the presence of a particle source in the plasma core and continues to peak until the increased core impurity radiation arrests the improved energy confinement, ultimately leading to a barrier collapse. With the addition of moderate (0.6 MW) central ICRF heating, the double barrier mode was maintained for as long as the ICRF power was applied. Modeling shows that the internal thermal barrier was maintained throughout the discharge. The presence of sawteeth throughout most of the ITB discharge allows sawtooth-induced heat pulse analysis to be performed. This analysis indicates that there is an abrupt radial discontinuity in the heat pulse time to peak profile when an ITB is present. Furthermore, this discontinuity appears to move into the core plasma from the edge region in about 0.2 s, several confinement times. The deduced thermal diffusivity, χhp, indicates that a barrier exists in the electron thermal transport, the barrier is limited to a narrow radial region, and the transport is unaffected outside this narrow radial extent. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1467347
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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Neutron calibration techniques for comparison of tokamak results (abstract) : Eighth topical conference on high-temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3232-3232 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A workshop on 1–3 August 1989 reviewed the techniques, uncertainties, and experiences of neutron calibration on PLT, TFTR, JET, Tore Supra, JT-60, JIPPT-IIU, Alcator C-Mod, ATF, FT, ASDEX, Textor, and DIII-D. In the summary session, the workshop participants discussed possible consensus neutron calibration techniques appropriate to D-D plasmas in tokamaks. The application of such techniques would facilitate a more accurate comparison of neutron yields from different devices, and also allow new calibration techniques to relate their precision to a reference value. General agreement was reached on the suitability of two techniques: (1) a 252Cf source calibration of epithermal neutron detectors, and (2) threshold neutron activation of Ni foils placed vertically above or below the plasma. This paper will present details on detector positioning, neutron transport calculations, and interlab normalization needed to accomplish the standardized calibration using a Cf neutron source.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141648
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