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  • 1
    Electronic Resource
    Electronic Resource
    Spectroscopy of plasmas with a multifiber commutator (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2015-2016 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Spatially resolved spectra have been obtained, during a single discharge, with one spectrometer using an optical multifiber commutator (OMC). We report results from this device which can be preprogrammed to select up to nine viewing chords, via high transmission optical fibers. This arrangement has been incorporated with a multichannel (OMA) spectrometer, where the fiber-to-fiber switching time matches the basic video scan of the detector (16 ms). The spectrometer can be operated in medium resolution mode (0.3 A(ring)) with a conventional grating or with high resolution (0.05 A(ring)) by substituting an echelle grating. The apparatus has been used for the evaluation of ion temperatures in the source and extraction regions of the Culham negative ion source. It is presently employed in JET for the study of the relative impurity influxes from the wall, the limiters, and the rf antennas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138775
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  • 2
    Electronic Resource
    Electronic Resource
    Coupling of an optical multichannel analyzer to a vacuum spectrometer using a photon convertor (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2038-2040 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Multichannel spectral devices that operate in the vacuum ultraviolet typically employ microchannel plates (MCP) detectors at the instrument focal plane. An alternative is to replace the MCP with a scintillator that converts the short wavelength light to the visible. A multichannel normal incidence spectrometer that incorporates a tetraphenyl-butadiene (TPB) scintillator has been coupled to an optical multichannel analyzer (OMA) by the use of high-quality camera lenses. These allow for magnification, or reduction, of the spectral image for high-resolution or spectral survey applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139203
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Advances in laser fluorescence scattering with Balmer series dye lasers (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1012-1014 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The spatial distribution of neutral deuterium has been determined in a reversed field pinch by fluorescence scattering. The first series of measurements, with a resolution of 4 cm were made with the laser tuned to the Dα, n=2−3(6561 A(ring)) transition. The second set of measurements, with both 4 and 2 cm resolution were performed with the laser tuned to the Dβn=2−4(4861 A(ring)) wavelength. The improvement in signal to noise obtained was substantial, being increased by a factor of (approximately-equal-to)2.5 in general. This is believed to be the first such measurement at this wavelength. The advantages of using this transition are such that this technique can be extended to measure the electron density near the plasma edge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138254
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  • 4
    Electronic Resource
    Electronic Resource
    Time-resolved ion temperature measurements on the HBTX1A reversed field pinch (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1103-1104 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The energy distribution of the neutral particle emission (200 eV–2 keV) from the HBTX1A reversed field pinch has been observed, using a five-channel analyzer, at 20-μs intervals throughout the duration of the discharge. The relative number of high-energy neutrals emitted increases with currents up to 250 kA above which there is little change. Preliminary analyses show that the ion temperature of the bulk of the plasma is in the range 70–120 eV, rather than the few electron volts expected from electron–ion collisions. Equally, the rapid evolution to this temperature (〈0.5 ms) is not accountable by equipartition (τeq∼3 ms). Long thermalization times (∼1 ms), compared with short time-scale excursions (∼100 μs) in the high-energy neutrals indicate that there are nonthermal ions at ∼10 times the Maxwellian temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138237
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  • 5
    Electronic Resource
    Electronic Resource
    Spectroscopic measurements on the Joint European Torus using optical fibers to relay visible radiation (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 862-864 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Light from the Joint European Torus (JET) tokamak is relayed by optical fibers to detectors outside the biological shield, where personnel access is unrestricted. This arrangement, which is described in detail, will permit routine recording during the intense neutron emission associated with the production of D–T plasmas—scheduled for 1989. The diagnostic has been in routine use since JET began operation in mid-1983. A selection of results obtained is presented. The likely degradation in fiber performance, due to irradiation, during the D–T phase of the program is assessed. Methods of overcoming the problems due to induced absorption are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138074
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  • 6
    Electronic Resource
    Electronic Resource
    CCD camera as a multichannel analyzer for the spectral and azimuthal resolution of Fabry–Pérot fringes (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1488-1490 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Fabry–Pérot interferometer is well known for its very favorable combination of high resolution and throughput. However, the radial dispersion of the spectrum makes multichannel detection difficult. Several systems have been devised that physically split the focal plane into annular elements, but these are normally limited to about ten channels while the Fabry–Pérot has potentially a much higher multichannel capability (e.g., the finesse is typically 20–50). In practice these devices have proved to be difficult to make. We have developed a more efficient and versatile technique where the interference pattern is focused onto a CCD array (640×1024 elements). The data can then be transformed to a circular coordinate system and, for example, provide the means of integrating all the information in selected annular ranges (i.e., a multichannel analyzer). The large number of pixels available enables a working finesse of up to 50 to be realized. The technique is particularly valuable for the detection of partial azimuthal fringes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139696
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  • 7
    Electronic Resource
    Electronic Resource
    Multichannel spectrometer for plasma diagnostics (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 552-559 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A multichannel vacuum ultraviolet spectrometer has been constructed to provide time-resolved measurements of line radiation from a plasma. The spectrometer may simultaneously view up to 40 preselected narrow spectral bands or lines from a common viewing chord in a wide spectral region (∼60–450 nm) with the maximum frequency response limited to 80 MHz by the photomultipliers and 350 kHz by the data-acquisition system. Rapid reselection of impurity lines is facilitated by the use of multiple slits cut in a metal foil placed at the Rowland circle of the instrument. Due to the limitation imposed by the present fiber-optic coupling to the plasma the results to date are from impurity wavelength in excess of about 220 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138870
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  • 8
    Electronic Resource
    Electronic Resource
    High-performance discharges in the Small Tight Aspect Ratio Tokamak (START) : 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. 1775-1783 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Small Tight Aspect Ratio Tokamak (START) [A. Sykes et al., Nucl. Fusion 32, 769 (1994)] spherical tokamak has recently achieved the record value of toroidal β∼30% in a tokamak-like configuration. The improvements that have made these results possible are presented along with a description of the global equilibrium parameters of the discharges. The ideal magnetohydrodynamic (MHD) stability of these discharges is analyzed, and they are found to be in close proximity to both the ballooning limit and the external current driven kink limit, but they are found to be far from the pressure driven external kink limit. Disruptivity for a range of shots is not correlated with the normalized β limit, but does correlate well with the empirical high-li disruption limit. The transport properties of these high-β equilibria are analyzed and compared to conventional tokamak scaling laws and transport models. The global transport is at least as good as that predicted by the ITER97-ELMy (edge-localized) scaling law. The local ion transport is in good agreement with that predicted by neoclassical models. The electron transport is anomalous, showing rough agreement with the Lackner–Gottardi transport model. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872819
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  • 9
    Electronic Resource
    Electronic Resource
    First physics results from the MAST Mega-Amp Spherical Tokamak : 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. 2101-2106 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: First physics results are presented from MAST (Mega-Amp Spherical Tokamak), one of the new generation of purpose built spherical tokamaks (STs) now commencing operation. Some of these results demonstrate, for the first time, the novel effects of low aspect ratio, for example, the enhancement of resistivity due to neo-classical effects. H-mode is achieved and the transition to H-mode is accompanied by a tenfold steepening of the edge density gradient which may enable the successful application of electron Bernstein wave heating in STs. Studies of halo currents show that these less than expected from conventional tokamak results, and measurements of divertor power loading confirm that most of the power flows to the outer strike points, easing the power handling on the inner points (a critical issue for STs). © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1352595
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  • 10
    Electronic Resource
    Electronic Resource
    The small tight aspect ratio tokamak experiment (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2481-2484 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-aspect-ratio tokamaks offer both the economic advantage of smaller size and a number of physics advantages which are not available at conventional aspect ratio. The Small Tight Aspect Ratio Tokamak (START) [Fusion Technology 1990, edited by B. E. Keen, M. Huguet, and R. Hemsworth (North-Holland, Amsterdam, 1991), Vol. 1, p. 353] was conceived as a first substantial test of tokamak plasma behavior at low aspect ratio. It has achieved plasma currents up to 200 kA, peak densities of ∼2×1020 m−3 and central electron temperatures of ∼500 eV at an aspect ratio of 1.3–1.5. Central beta values of ∼13% have been measured and the volume-averaged beta 〈β〉 can approach the Troyon limit. Plasmas are naturally elongated (κ(approximately-less-than)2.0) and are vertically stable without feedback control. Major disruptions have not been observed at low aspect ratios (A≤2.0).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860732
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