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  • 1
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    Operational conditions and characteristics of ELM-events during H-mode plasmas in the stellarator W7-AS (2000)
    Institute of Physics
    Details
    Publication Date: 2000-05-01
    Print ISSN: 0741-3335
    Electronic ISSN: 1361-6587
    Topics: Physics
    Published by Institute of Physics
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    PAPER CURRENT
  • 2
    Electronic Resource
    Electronic Resource
    Survey of magnetohydrodynamic instabilities in the advanced stellarator Wendelstein 7-AS (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 931-956 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetohydrodynamic (MHD) instabilities in the Wendelstein 7-AS stellarator (W7-AS) [G. Grieger et al., Phys. Fluids B 4, 2081 (1992)] are characterized experimentally in various plasma parameter regimes and heating scenarios. The observations are compared with theoretical predictions for particular cases. In the high-β range (〈β〉≤2%) no clear evidence of a stability β-limit could be found yet. In the lower β regime fast particle driven global Alfvén modes are the most important instabilities during neutral beam injection (NBI). Besides of coherent modes with almost no effect on the plasma performance additional Alfvén modes appear at higher frequencies up to 400 kHz, which show nonlinear phenomena-like bursting, frequency chirping, and MHD induced energy and fast particle losses. The activity of edge localized modes (ELMs) is investigated in NBI heated discharges. The issue of current driven instabilities and their potential stabilization by a stellarator field has been investigated with regard to the design of compact hybrid stellarator systems. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1346633
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature fluctuations and their correlation with density fluctuations in W7-AS : 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. 1014-1017 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Correlations between electron density and temperature fluctuations have been measured in the core plasma of W7-AS. The simultaneous use of transmitting and receiving antennas of a heterodyne reflectometer by a crossed sightline ECE correlation radiometer enables the cross-correlation analysis of the reflectometer phase signal and ECE radiation temperature signals in overlapping plasma volumes. Correlations have been found in the spectral range 25–100 kHz, indicating an in-phase correlation between electron density and temperature fluctuations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149291
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  • 4
    Electronic Resource
    Electronic Resource
    Tomography by the maximum entropy method for the W7-AS and W7-X multichannel bolometer systems : 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. 762-765 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A maximum entropy approach has been applied to the tomographic inversion of the line integrated measurements of radiation power flux by a multichannel bolometer system. This method was applied to an H-mode discharge in the W7-AS stellarator, with increasing radiation from the plasma core after the transition being observed. Also, a neutral beam injection discharge was investigated, and the time evolution of a marfe was documented. This method has also been applied to the preliminary design of a multicamera system for full tomographic reconstruction in the W7-X stellarator. In addition, measurements with wire mesh shielded metal foil bolometers have been carried out and the shielding of these bolometers from microwaves produced by the 140 GHz gyrotrons used for electron cyclotron heating has been demonstrated. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147912
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  • 5
    Electronic Resource
    Electronic Resource
    Amplitude modulated heterodyne reflectometer for density profile and density fluctuation profile measurements at W7-AS (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1807-1813 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A broadband heterodyne reflectometer operating in the frequency range 75–110 GHz in extraordinary mode polarization is used at the W7-AS stellarator for both fast density profile determination and density fluctuation studies. The probing signal is amplitude modulated at a frequency 133 MHz using the envelope phase for profile evaluation and the carrier phase to determine the fluctuation information simultaneously. Separate Gaussian beam optics for final signal launch and detection permits a beam waist of about 2 cm at the reflecting layer in the plasma. Amplitude modulated detection is accomplished in the intermediate frequency part by synchronous detection after recovery of the carrier by narrow-band filtering. Voltage controlled solid state oscillators followed by active frequency multiplication allow to scan the full frequency band within less than 1 ms. For typical W7-AS operation the accessible density range is 1×1019 to 6×1019 m−3 for on axis magnetic field of 2.5 T and 4.5×1019 to 10×1019 m−3 for 1.25 T, respectively. The probed radial positions range between 0.2〈r/a〈1.1 depending on plasma conditions (a≈17 cm). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146978
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  • 6
    Electronic Resource
    Electronic Resource
    Broadband heterodyne reflectometer at the W7-AS stellarator (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2284-2290 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A broadband heterodyne reflectometer, operating in the frequency range 75–110 GHz in extraordinary mode polarization, has been installed and operated at the Wendelstein 7-AS stellarator for the study of density fluctuations and density profile determination. At 2.5 T it covers the density range between 5×1018 and 5×1019 m−3. The system differs from the usual setup as it combines the advantages of heterodyne detection with broadband capability avoiding the limitations of phase-locked sources and permits the unambiguous determination of the phase delay independent of amplitude fluctuations in the reflected beam. After a first downconversion to an intermediate frequency of about 6 GHz, two additional mixing steps lead to an intermediate frequency of 60 MHz, which carries the phase delay from the plasma as a phase modulation. The phase information is yielded numerically from sin/cos detection at 60 MHz. Due to the balanced detection scheme, the drift as well as the broadband noise of the signal and local oscillators are canceled. The system has a dynamic range of about 60 dB and is within this range almost insensitive to amplitude fluctuations of the reflected beam. Examples are given demonstrating the potential of the system installed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144678
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  • 7
    Electronic Resource
    Electronic Resource
    Heterodyne reflectometer for phase and time delay measurements in W7-AS : 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. 412-412 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A broadband heterodyne reflectometer operating in the frequency range 75–110 GHz in extraordinary mode polarization, is used at the W7-AS stellarator for density profile and density fluctuation studies. The system allows for broadband operation and permits unambiguous determination of the phase delay independent of the amplitude fluctuations in the reflected beam. The system uses two different gauss beam optics for both signal launch and detection with a slim beam waist of about 2 cm at the relevant plasma location. An amplitude modulation system has been incorporated operating at 133 MHz modulation frequency sharing with the phase sensitive system the main oscillators, antennas, and the receiver front end. AM detection is accomplished in the IF part by synchronous detection after recovery of the carrier by narrowband filtering. Time delay measurements can be done simultaneously with the carrier phase determination. The main purpose of the diagnostic in AM mode is fast edge density profile monitoring, conventional carrier phase detection is used for density fluctuation measurements and planned correlation studies. The agreement between the WKB approximation and the 1 D full wave numerical solutions for the W7-AS parameters and geometry guarantees the good localization of the measurements and permits the estimation of density fluctuation level from the measured phase fluctuations. Density fluctuation studies have been carried out in NBI and ECRH (L- and H-mode) plasmas. Fluctuation levels and spectral characteristics have been analyzed. In addition 2D effects possibly due to rotating turbulent structures have been observed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146363
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  • 8
    Electronic Resource
    Electronic Resource
    Permittivity and Permeability of Mullite-SiC-Whisker and Spinel-SiC-Whisker Composites (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Real and imaginary permittivity (ɛ′ and ɛ″, respectively) values were determined on mullite-silicon carbide whisker (mullite-SiCw) composites, mullite-ZrO2 composites, and spinel-SiCw composites, in the frequency range of 2-18 GHz, using a 14 mm coaxial air-line measurement system. Depending on the frequency, the addition of 30 vol% of SiCw to mullite increases ɛ′ from 6.6-6.9 to 16-22 and increases ɛ′ from 0 to 16-22. The addition of 32 vol% of SiCw to spinel increases ɛ′ from 7.5-7.8 to 37-44 and increases ɛ″ from 0 to 13-20. The addition of 21 vol% of ZrO2 to mullite increases ɛ″ to ∼9 but does not change ɛ″. Real and imaginary permeability values were 1 and 0, which are within experimental error.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02452.x
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  • 9
    Electronic Resource
    Electronic Resource
    A calibration curve for room-temperature resistivity versus donor atom concentration in Si:As (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 3779-3783 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron activation measurements of arsenic concentration have been made on a set of samples cut from melt-grown crystals of Si:As in the concentration range from 7.8×1018 cm−3 to 1.1×1019 cm−3. Measurements of electrical resistivity at room temperature on the same samples provide information for a calibration curve of resistivity ρ versus the donor concentration nD. The data are combined with earlier measurements of ρ and nD made by Backenstoss using radioactive tracer techniques at lower As concentration to yield a calibration curve covering the donor concentration range from 1.0×1018 cm−3 to 1.1×1019 cm−3. A fourth-order polynomial expression for the function ρ vs nD is compared with data derived from Hall constant determinations of donor concentration. Using the expression relating the Hall constant to the electron density, RH=A(nD)/ne, we are able to obtain values of the function A(nD) for arsenic concentrations in the range 3.0×1018 cm−3 to 8.6×1018 cm−3. These values for Si:As are compared to the A(nD) values for Si:P.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335591
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  • 10
    Electronic Resource
    Electronic Resource
    Pressure-Temperature Chart for Vapors (1942)
    s.l. : American Chemical Society
    Industrial & engineering chemistry 34 (1942), S. 174-182 
    Details
    ISSN: 1520-5045
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ie50386a011
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