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  • 1
    Electronic Resource
    Electronic Resource
    Modification of tokamak edge turbulence using feedbackf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1606-1611 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using active feedback, the turbulent fluctuation levels have been reduced by as much as a factor of 2 in the edge of the Texas Experimental Tokamak (TEXT) [K. W. Gentle, Nucl. Fusion Technol. 1, 479 (1981)]. A probe system was used to drive a suppressor wave in the TEXT limiter shadow. A decrease in the local turbulence-induced particle flux has been seen, but a global change in the particle transport at the present time has not been observed. By changing the phase shift and gain of the feedback network, the amplitude of the turbulence was increased by a factor of 10.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870661
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  • 2
    Electronic Resource
    Electronic Resource
    On the role of neutral particles on edge turbulence and electric fields in the Advanced Toroidal Facility (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3-5 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of edge plasma turbulence properties have been carried out in the Advanced Toroidal Facility (ATF) [Fusion Technol. 10, 179 (1986)] during experiments in which hydrogen and neon gas puffing are used to vary the edge temperature in the range 5〈Te〈40 eV in a controlled way. In the temperature range where the rate coefficients for ionization processes are strongly temperature dependent (5〈Te〈15 eV) the electron temperature plays an important role in determining the level of edge turbulence and the value of the self-generated radial electric fields. These results provide evidence of edge turbulence and flows modified by the presence of neutral particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870556
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  • 3
    Electronic Resource
    Electronic Resource
    A comparison of edge turbulence in tokamaks, stellarators, and reversed-field pinches* (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2491-2497 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Edge equilibrium, turbulence and transport related plasma parameters from the Advanced Toroidal Facility (ATF) [Fusion Technol. 10, 179 (1986)] torsatron, the ZT-40M [Fusion Technol. 8, 1571 (1985)] reversed-field pinch, the Phaedrus-T [Nucl. Fusion 32, 2040 (1992)] tokamak, the Texas Experimental Tokamak (TEXT) [Nucl. Technol. Fusion 1, 479 (1981)], and the Tokamak Fusion Test Reactor (TFTR) [in Plasma Physics and Controlled Nuclear Fusion Research, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 1, p. 9] have been obtained using a standardized Langmuir probe array and a consistent set of data analysis packages. Additional data from some other devices have also been furnished via private communications and incorporated from published results. Experimental results over a wide range of parameters are compared and the turbulence contribution to edge transport are assessed. Certain physical properties that are relevant to the modeling of edge turbulence are identified: namely, shear decorrelation of turbulence, the role of resistive dissipation and electron parallel thermal conduction, radial mode structure in sheared magnetic field, and electromagnetic contribution to the parallel Ohm's law.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860734
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  • 4
    Electronic Resource
    Electronic Resource
    Characteristics of edge plasma turbulence on the ATF torsatron (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1000-1005 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of electrostatic fluctuations on the edge of the Advanced Toroidal Facility (ATF) torsatron [Fusion Technol. 10, 179 (1986)] are used to study the role of the edge turbulence in the particle transport in this current-free magnetic configuration. Spatial profiles of the plasma electron density ne, temperature Te, and fluctuations in density (ñe) and in the plasma floating potential (φ˜f ) are measured at the edge in electron cyclotron heated plasmas using a Langmuir probe array. At the last closed flux surface (LCFS), r/a≈1, Te≈20–40 eV, and ne≈1012 cm−3 for a line-averaged electron density n¯e=(3–6)×1012 cm−3. The relative fluctuation levels decrease as the probe is moved into the core plasma. For Te(approximately-greater-than)20 eV, ñe/ne≈5%, and eφ˜f /Te≈2ñe/ne at r/a=0.95. The measured fluctuation spectra are broadband (40–300 kHz) with k¯ρs≈(0.05–0.1), where k¯ is the average wave number of the fluctuations and ρs is the ion Larmor radius at the sound speed. Near the LCFS, the density fluctuations can be approximated by ñe/ne ≈0.4/k¯Ln, where Ln is the gradient scale length of ne. The propagation direction of the fluctuations reverses to the electron diamagnetic direction at r/a〈1. The phase velocity of the fluctuations and the electron drift velocity are comparable. The particle flux estimated from the fluctuations is consistent with fluxes obtained from the particle balance using the Hα spectroscopic measurements. Many of the features seen in the ATF edge fluctuations resemble those of Ohmically heated plasmas in the Texas Experimental Tokamak (TEXT) [Phys. Rev. Lett. 62, 1844 (1989)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859882
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  • 5
    Electronic Resource
    Electronic Resource
    High-field launch electron-cyclotron heating experiments in a bumpy torus (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 318-327 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The midplane microwave heating system in the ELMO Bumpy Torus (EBT) [in Proceedings of the Sixth International Conference on Plasma Physics and Controlled Nuclear Fusion Research, 1976 (IAEA, Vienna, 1977), Vol. II, p. 145] was supplemented with power launched from the high-field side of the fundamental resonance by an antenna in the magnet coil throat. Up to 43 kW of polarized (extraordinary mode), 28 GHz power was successfully launched with one antenna. Measurements were made of changes in the core and hot-electron ring plasma parameters when throat-launch power was added. In sharp contrast to initial expectations, the bulk core-plasma parameters were degraded while the ring parameters, in the launch cavity, were improved. These results are consistent with a modified picture of electron-cyclotron heating (ECH) in EBT. A picture of localized microwave absorption and particle losses is supported by additional measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865943
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  • 6
    Electronic Resource
    Electronic Resource
    Electron confinement in a bumpy torus without the influence of hot-electron rings—"Ring killer'' experiment (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2848-2856 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ELMO Bumpy Torus (EBT) [Plasma Physics and Controlled Nuclear Fusion (IAEA, Vienna, 1975), Vol. II, p. 141] normally has an energetic electron ring in each of its 24 mirror sectors. The original intention of using this hot-electron population was to provide an average local minimum in the magnetic field (through its diamagnetism) to stabilize the simple interchange and flute modes, which otherwise are theoretically inherent in a closed-field-line bumpy torus. To study the confinement properties of a bumpy torus without the influence of hot-electron rings, a water-cooled stainless steel limiter in each mirror sector was extended into the plasma to the ring location; this eliminated the hot-electron ring population. These limiters were aptly named "ring killers.'' Electron temperature, density, space potential, and plasma fluctuations have been measured during the ring killer experiment and are compared to standard EBT operation. The results of these experiments indicate that the hot-electron rings in EBT do enhance the core plasma properties of EBT and do, in fact, reduce plasma fluctuations; however, these improvements are not large in magnitude. These measurements and recent theoretical models suggest that simple interchange/flute modes are stabilized, or fluctuation levels reduced, well before that condition is obtained for average minimum-B stabilization. Several possible mechanisms for this stabilization are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865205
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  • 7
    Electronic Resource
    Electronic Resource
    The electron distribution function in a bumpy torus (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 1922-1931 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: New and improved diagnostic techniques and increased theoretical understanding of electron-cyclotron heating (ECH) have led to a new picture of the electron distribution function in the ELMO Bumpy Torus (EBT). For electron energies ≤2 keV, the distribution function can be approximated as consisting of two components: a cold isotropic bulk component and a warm anisotropic tail. For typical steady-state EBT-Scale (EBT-S) operation (microwave power input of 100 to 150 kW) in the T-mode (the operating mode of interest for fusion experiments), bulk densities and temperatures of ne =0.5–0.7×1012 cm−3 and Te ≤100 eV are observed, while the warm tail component has Te =200–800 eV, and densities ≤0.4 that of the cold component. The non-Maxwellian nature of the distribution function is caused by ECH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.864936
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  • 8
    Electronic Resource
    Electronic Resource
    Electron density profile measurement with a heavy ion beam probe : 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. 4571-4573 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The feasibility of electron density profile measurements using a heavy ion beam probe in high-temperature plasmas has been demonstrated earlier [J. Schwelberger et al., Bull. Am. Phys. Soc. 36, 2292 (1991); Yu. N. Dnestrovskij et al., Sov. J. Plasma Phys. 12, 130 (1986)]. Two algorithms were developed to obtain density profiles from the heavy ion beam probe on the Advanced Toroidal Facility (ATF). A comparison of the algorithms is presented with a detailed study of the errors involved in the measurements. The errors can be due to uncertainties in cross sections, electron temperature, the line average density measurement, and the ion trajectory calculations. The heavy ion beam probe density profile measurement is not very susceptible to errors as long as the electron temperature stays above 30 eV. If the electron temperature is below this value, a small uncertainty in the temperature introduces a large error in the density. Also, important for a good density profile measurement is the calculation of the correct ion trajectories. Examples of density profiles are shown for ECH plasmas on ATF together with a detailed error analysis. The heavy ion beam probe results are in good agreement with multichannel far-infrared laser interferometry and Thomson scattering results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143671
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  • 9
    Electronic Resource
    Electronic Resource
    An amplifier for use with large-area photodiodes (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3909-3910 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a high-gain (∼107) amplifier for use with large-area silicon photodiodes for monitoring the intensity of plasma light from fusion experiments. To achieve the necessary gain without saturating the output signal, the amplifier design incorporates a bootstrap technique and capacitive coupling between amplifier stages. This design eliminates voltage offset at the amplifier output due to detector leakage, while retaining desirable low-frequency response characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141522
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  • 10
    Electronic Resource
    Electronic Resource
    Wave launching as a diagnostic tool to investigate plasma turbulence (abstract) : 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. 440-440 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An experimental scheme to extend the investigation of plasma turbulence has been implemented. It involves driving waves into the plasma to modify the statistical properties of the fluctuations; the dynamical balance of the turbulence is perturbed via the injection of waves at selected spectral regions. New analysis techniques based on conditional sampling and high order correlation are developed for studying the wave launching and the wave-wave coupling processes. Experimental results from TEXT-U tokamak show that the launched waves interact with the intrinsic fluctuations both linearly and nonlinearly. The attainment of driven nonlinearity is necessary for this diagnostic scheme to work. It is also the key to an active modification and control of edge turbulence in tokamaks. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146374
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