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  • 1
    Electronic Resource
    Electronic Resource
    Double parallel-plate electrostatic analyzer for Tara end-loss studies (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1789-1791 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An endloss spectrograph has been designed and is being fabricated for the Tara tandem mirror. This spectrograph is a double parallel-plate electrostatic analyzer about 60 cm in length with a 30° entrance angle; the high-voltage plate is a transparent wire cloth grid which allows higher energy particles to pass through for detection on a symmetric ground plane. The analyzer has three detection planes: first, the normal focal plane for low-energy detection at high resolution (0.1–4 keV); second, the entrance grounded plate for mid energies (4–6 keV); and third, the symmetric ground plane for coarse resolution at higher energies (8–20 keV). The analyzer is defocusing on the symmetric plane. This spectrograph will be able to measure simultaneously the endloss potential cutoff and ions from the neutral beams; in conjunction with a loss cone neutral beam source the resolution is sufficient (60 eV) to measure the plasma potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139183
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  • 2
    Electronic Resource
    Electronic Resource
    Acousto-optic spectrum analyzer for plasma diagnostics (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 1387-1392 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An acousto-optic rf spectrometer (AOS) has been designed and constructed for use on the CONSTANCE B and TARA mirror experiments at MIT. The AOS is an analog preprocessor of data that can come from a variety of sources, including rf probes and microwave/laser scattering experiments. The output of the AOS is the Fourier transform amplitude of the input in a parallel format suitable for computer acquisition. The spectrometer, having a bandwidth of 500 MHz and a resolution of 1 MHz, together with its receiver, is capable of looking at fluctuations anywhere in the frequency range of a few MHz up to 4 GHz. Power levels of a few nanowatts can be detected. Complete 500-MHz-wide spectra can be processed and acquired at the rate of 1 every 10 μs. The optical components, receiver, and data-acquisition interface will be discussed, and initial data taken on the CONSTANCE B experiment will be shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139419
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Two-color interferometer system for Alcator C-MOD (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1568-1570 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: High densities with sharp, fast rising profiles are expected during pellet injection in Alcator C-MOD. Consideration of interferometer systems other than far infrared will be needed to avoid refractive effects and make profile measurements during pellet injection possible. CO2 wavelengths are proving to be the most interesting from the standpoint of density measurements, with the necessary vibration subtraction provided by a coaxial He:Ne system. We will describe the two-color interferometer as it is presently designed and present results from simulations made of the system to determine noise levels, minimum measurable density, and optimal number and location of chords. Ray tracing results both with and without pellet injection will be compared. Possible fringe counting schemes will also be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140199
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  • 4
    Electronic Resource
    Electronic Resource
    Multichord interferometer for edge density profiles in Alcator C-Mod (abstract) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1591-1591 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The preliminary design of a multichord imaging interferometer system used to measure the density profiles in the scrape-off layer of the Alcator C-Mod tokamak is presented. The system is envisioned to be a two-color vibration compensated double-pass interferometer based on a CO2 laser with λ=10.6 μm; the second color will either use He–Ne emission at 632.8 nm or 3.39 μm, depending on how serious the vibrations are expected to be. A toroidal view of the plasma near the vertical midplane is considered. We present systematic studies of the requirements on fringe resolution and edge density range, from which reasonably accurate profiles can be inferred. Requirements on the spatial resolution, number of detectors, and the possibility of obtaining 2-D images of the edge will be addressed. Longer wavelength alternatives using a FIR laser will also be studied; in this case the main concern is beam refraction caused by the density gradients in the edge region of interest. This work was supported by U. S. DOE Contract No. DE-AC02-78ET51013.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140154
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  • 5
    Electronic Resource
    Electronic Resource
    Operation of an E (parallel) B end-loss ion spectrometer on the Tara tandem mirror (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1664-1666 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An E (parallel) B end-loss ion spectrometer from the Livermore TMX-U tandem mirror experiment was installed on Tara for high-resolution ion spectroscopy. This diagnostic contains parallel electric and magnetic fields, separating the masses and energies of the ions over 128 collector plates. The ion energy distribution nominally yields confining potentials and parallel ion temperatures. Additional experiments have diagnosed the resonance position of the central cell ion cyclotron heating, rf enhanced losses of high-energy sloshing ions in the axicell ("plug''), and observation of MHD instabilities at higher time resolution (20 kHz).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140126
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  • 6
    Electronic Resource
    Electronic Resource
    Pseudotomographic fitting algorithm for density profile reconstruction from a sparse 1-D interferometer array (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1067-1071 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An algorithm has been developed for fast analysis of a sparse multichord interferometer array, yielding peak density, Gaussian width, radial offset, ellipticity, and instability amplitude and frequency from line-integrated density measurements. A nonlinear least-squares fit is performed over many short time intervals, with independent variables reduced to one dimension. Assumptions of plasma rigidity and slowly evolving rotation rate are necessary to trade temporal resolution (on instability timescales) for spatial resolution across the moving plasma column. Results from the Tara tandem mirror experiment are shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139727
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of neutral particles on edge dynamics in Alcator C-Mod plasmas : 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. 1919-1926 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutral particle densities and energy losses have been measured in the Alcator C-Mod tokamak [Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. Their effect on the formation and evolution of the edge barrier which accompanies the enhanced confinement regime are discussed. The neutrals can enter the edge dynamics through the particle, momentum, and energy balance. Neutral densities of up to 5×1016 m−3 have been measured in the edge barrier region. Neutrals enter the local dynamics around most of the periphery, not just at the X-point. High resolution measurements of the ionization profile have been obtained for the region near the separatrix. The profile shifts inside the separatrix as the plasma is making a transition from low-to high-mode confinement (H-mode) regimes, partly accounting for the dramatic rise in edge density. The measured neutral density is large enough to affect the bulk ion momentum by charge exchange, and thereby introduces a negative radial electric field at the edge. At the same time, significant edge heat flux, carried by the neutrals, contributes to the measured power loss. At very high edge densities, this loss mechanism could contribute to quenching H-modes. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874016
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  • 8
    Electronic Resource
    Electronic Resource
    Measurements of the high confinement mode pedestal region on Alcator C-Mod : 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. 1744-1751 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of the steep transport barrier at the edge of the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] are presented. The parameters at the top of this barrier are in the range Te=150–750 eV and ne=0.5−3.3×1020 m−3, depending on the confinement regime. Type III edge localized modes (ELMs) have an upper temperature limit. Te pedestal profiles show a barrier width ΔT(similar, equals)8 mm. Soft x-ray emissivity profiles are narrower, with Δ=2–4 mm. Edge currents are calculated to alter the ideal stability boundary favorably, leading to ideally stable pedestal profiles. High frequency, broadband, edge density fluctuations are sometimes observed in H-mode (high-confinement mode) and are associated with enhanced particle transport. Coherent magnetic fluctuations localized near the pedestal are also seen. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872843
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  • 9
    Electronic Resource
    Electronic Resource
    Experimental study of nonlinear M=1 modes in the Tara tandem mirror (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 902-907 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nature of a rigid, flutelike M=1 instability as seen in the Tara tandem mirror [Nucl. Fusion 22, 549 (1982); Plasma Physics and Controlled Nuclear Fusion 1984 (IAEA, Vienna, 1985), Vol. 2, p. 285] is discussed. Radial density and light emission profiles obtained by inverting chord measurements are compared to end loss radial profiles during the evolution of the mode to its nonlinear saturated state. This final state is characterized by a coherent, flutelike motion of the plasma as a whole about the machine axis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866773
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  • 10
    Electronic Resource
    Electronic Resource
    Experimental studies of divertor stabilization in an axisymmetric tandem mirror (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 2009-2016 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A divertor coil set has been installed on the Tara tandem mirror [Nucl. Fusion 22, 549 (1982); Plasma Physics and Controlled Nuclear Fusion Research 1984 (IAEA, Vienna, 1985), Vol. 2, p. 285] for stabilization of m=1 flutelike modes. The effectiveness of divertor stabilization is discussed in experiments where m=1 modes are driven to instability by plug electron cyclotron heating (ECH) in an ion cyclotron heated (ICH) plasma. The instability onset is characterized by thresholds in ECH power, fueling rate, ICH power, and mapping radius of the divertor null. In general, the stability is enhanced by mapping the null radially inwards into the plasma. The interdependence of these parameters and their effect on equilibrium profiles and stability boundaries are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866649
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