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  • 1
    Electronic Resource
    Electronic Resource
    Observation of up-down asymmetric impurity densities in TEXT from a horizontal x-ray imaging array (abstract) : Eighth topical conference on high−temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3149-3149 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Up-down asymmetries were observed in the x-ray emission from aluminum injected into TEXT [K. W. Wenzel et al., Bull. Am. Phys. Soc. 34, 2153 (1989)]. The Z dependence of these asymmetries will be explored by injecting carbon, aluminum, titanium, chromium, and iron into similar TEXT discharges. Furthermore, the current-direction dependence will be tested. The latter experiment may clarify coupling between impurity density asymmetries and electron density fluctuation asymmetries, because the fluctuation asymmetries were found to reverse with changed current direction [D. L. Brower et al., Phys. Rev. Lett. 54, 689 (1985)]. A possible theoretical coupling between impurity density and fluctuation asymmetries comes from the effect of radiative cooling on thermally driven convection cells [D. R. Thayer and P. H. Diamond, Phys. Fluids 30, 3724 (1987)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141667
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  • 2
    Electronic Resource
    Electronic Resource
    Improved performance of an optically pumped FIR laser using metallic waveguide : 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. 4672-4674 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In order to improve the overall output characteristics of far-infrared (FIR) lasers, recent development at UCLA has concentrated on the use of a metallic overmoded waveguide (smooth bore and corrugated) instead of a conventional smooth-bore dielectric waveguide. The metallic waveguide has substantially lower propagation losses, especially at frequencies below 500 GHz, and also supports the desired HE11 mode. Laboratory results show a substantial increase in output power using a corrugated metallic waveguide, with 37 mW being obtained at 1.22 mm using 13CH3F (isotopic methyl fluoride) while maintaining the same mode quality and polarization. This represents an improvement of 100% over a smooth-bore dielectric waveguide. Comparison of far-infrared output using the three types of waveguide will be made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143659
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  • 3
    Electronic Resource
    Electronic Resource
    Fluctuation measurements in the DIII-D and TEXT tokamaks via collective scattering and reflectometry (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3509-3519 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Anomalous transport in fusion plasmas remains an enigma requiring explanation. A predictive capability is highly desirable if confinement enhancement regimes such as H mode or super shots are to be extrapolated to the next phase in development of the International Fusion program, epitomized, for example in ITER. Therefore, identification of the role that electrostatic turbulence plays in confinement is a critical issue requiring detailed experimental data capable of testing and challenging existing theoretical models. This article presents microturbulence measurements obtained on the DIII-D and TEXT tokamaks utilizing heterodyne, far-infrared collective scattering, and reflectometry techniques. The experimental systems are described on both machines and emphasis placed on results obtained during the L-H transition, ELM activity, and saturated ohmic operation where ion temperature gradient driven (ITGD) turbulence is theoretically predicted to exist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141560
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  • 4
    Electronic Resource
    Electronic Resource
    UCLA FIR diagnostic systems on TEXT and developments for TEXT Upgrade (abstract) : Eighth topical conference on high−temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3071-3071 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A multipurpose multiview far-infrared diagnostic system is being designed and constructed for the TEXT Upgrade. The system's capabilities, designed to enhance the applications of the present FIR system on TEXT, will include two-view interferometry, polarimetry, and collective scattering in order to measure the plasma density profile, current profile, and density fluctuation distribution. The interferometer/polarimeter system will possess high spatial (Δx=1.5 cm) and high-density (≤5×1010 cm−3) resolution. Tomographic reconstruction techniques will be employed to investigate both the equilibrium and perturbed profiles of plasma density. This represents an extension of the present work on TEXT where MHD effects such as sawteeth, Mirnov oscillations, and disruptions have been studied. Two-view multichannel collective scattering (1≤k⊥≤20 cm−1) will allow the kr and kθ spectra to be measured simultaneously. Heterodyne detection permits the wave propagation direction and multiple modes to be resolved unambiguously. Cross correlation of signals from each view may produce significant improvement in the scattering system spatial resolution. A reflectometry system will also be installed to study fluctuations and provide more localized measurement. This work was supported by U.S. DOE contract No. DE-FG03-86ER-53225 and DE-FG03-88ER-53267.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141733
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  • 5
    Electronic Resource
    Electronic Resource
    Poloidal asymmetry and gradient drive in core electron density and temperature fluctuations on the Texas Experimental Tokamak-Upgrade (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2013-2021 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron temperature and density fluctuations are measured in the core of the Texas Experimental Tokamak-Upgrade (TEXT-U) [P. H. Edmonds, E. R. Solano, and A. J. Wootton, in Proceedings of the 15th Symposium on Fusion Technology, Utrecht (Elsevier Science, Amsterdam, 1989), Vol. 1, p. 342] plasma across the poloidal cross section. The high spatial resolution of the heavy-ion beam probe (HIBP) and correlation radiometry of electron cyclotron emission (CRECE) reveal that both the density and temperature fluctuations are strongly poloidally asymmetric. Temperature fluctuation measurements indicate a broadband drift wave feature localized near the plasma equatorial plane on both the high- and low-field sides, which is consistent with density fluctuation measurements by far infrared (FIR) scattering. In contrast, the HIBP observes this feature localized only to the low-field side. Excellent spatial resolution allows us to investigate whether changes in the gradient affect the fluctuation amplitudes. We find that indeed, the temperature fluctuations increase with the electron temperature gradient. Results also link density fluctuations to changes in the density gradient. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871998
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  • 6
    Electronic Resource
    Electronic Resource
    Interferometric measurement of high-frequency density fluctuations in Madison symmetric torus : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 703-706 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: As a consequence of recent improvements to the far-infrared (FIR) interferometer time response, from bandwidth of 10 kHz up to 1 MHz, high-frequency density fluctuations can now be resolved on the Madison symmetric torus (MST) reversed-field pinch. The phase measurement allows absolute calibration of the fluctuation amplitude while eleven chords generate information on the spatial distribution. Density fluctuations up to 200 kHz are observed. A unique feature of the MST interferometer is that six chords are toroidally displaced 5° from the remaining five. Hence, besides information on the poloidal structure, i.e., m=1, toroidal information is also available. By computing the cross power, coherence, and cross phase between two toroidally displaced chords, one can determine the toroidal rotation speed, dispersion, and correlation length. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149275
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  • 7
    Electronic Resource
    Electronic Resource
    Initial operation of the two-dimensional far-infrared scattering/interferometry system on TEXT-Upgrade : 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. 856-858 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The UCLA far-infrared scattering/interferometry system on TEXT-Upgrade has recently been modified to include a two-dimensional capability. Along with the vertically viewing system, a horizontal view has been added. For interferometric measurements of the plasma density profile, the vertical view consists of a 45 cm array while the horizontal view array spans 15 cm. Density profiles for Text-Upgrade plasmas will be presented. For collective scattering measurements of electron density fluctuations, cross correlation of scattered signals from the two orthogonal views at the same wave vector will be examined. Finite cross coherence may be used to spatially localize the fluctuation measurements. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146252
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  • 8
    Electronic Resource
    Electronic Resource
    Multichannel far-infrared polarimeter-interferometer system on the MST reversed field pinch : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1077-1080 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The multichannel far-infrared (FIR) heterodyne polarimeter-interferometer system on the Madison Symmetric Torus (MST) is now operational. The combined system consists of 11 channels with variable radial and toroidal spacing. Poloidal magnetic field is determined by measuring the Faraday rotation of the FIR laser beam after propagation through the plasma by use of a phase technique. The polarimeter has 3 mrad rms noise level and 1 ms temporal resolution while the interferometer resolution is nedl=1×1012 cm−2 with time response of 1 μs. Absolute calibration of the polarimeter system is achieved by use of a rotating quartz half-wave plate. The first 11-channel polarimeter measurements from MST indicate a Faraday rotation profile in good agreement with expectations from the MSTFIT equilibrium code. Future plans to reduce the polarimeter time response from 1 ms to 10 μs will allow direct measurement of magnetic fluctuations associated with global resistive tearing modes on MST. The effect of these modes on density is already clearly resolved and provides insight into the dynamics of these structures. Improving the time response will also result in lower phase noise for both the polarimeter and interferometer. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1321744
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  • 9
    Electronic Resource
    Electronic Resource
    Application of a digital phase comparator technique to interferometer data : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 902-905 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Substantial improvements have been made to increase the frequency bandwidth of the UCLA multichannel interferometer system on TEXT-Upgrade. Recently, a digital phase comparator technique was implemented that has several advantages over the conventional analog phase comparator. The probe and reference wave forms are directly digitized and the phase computed in software using a numerical demodulation algorithm. For the purpose of reducing the data load, aliasing of the laser difference frequency is employed to vary the time response according to experimental demands. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147765
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  • 10
    Electronic Resource
    Electronic Resource
    Vacuum compatible, variable cross-section magnetic coil diagnostic used in digital feedback control of plasma position in TEXT-Upgrade : 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. 461-463 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A magnetic pickup coil diagnostic set is used to measure the position of the plasma column in the Texas Experimental Tokamak Upgrade (TEXT-U) project. The output from this coil set is used in a digital feedback system to control the plasma position. To provide a fast time response for the feedback system, one complete coil set is located on the interior of the vacuum vessel. Another set with a slower time response is located on the outside of the vessel. To simplify and speed up data processing, the coils are constructed so that the X and Y coordinates of the plasma current centroid are each determined using the signals from only two separate coils. For each coordinate one coil is used to measure a tangential (relative to the coil surface) magnetic field component, while the second coil measures a normal field component. Due to physical constraints, the coils are not continuous around the vacuum vessel. The presence of gaps in the coils causes pickup of the external current flowing in the divertor coil windings during TEXT-U diverted discharges. This pickup has been successfully nulled out by adding a divertor current Rogowski coil to the X position coil circuit. The data indicate that these coils, along with the digital feedback system, are useful tools for flexible position control over a wide range of TEXT-U plasma parameters. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146383
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