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  • 1
    Electronic Resource
    Electronic Resource
    Broadband density fluctuation measurements using a heavy ion beam probe on the Texas Experimental Tokamak (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3360-3367 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Broad bandwidth (60 kHz ≤f≤500 kHz), long wavelength (k¯θ≤2 cm−1) density fluctuation measurements were made using a heavy ion beam probe on the Texas Experimental Tokamak (TEXT) [K. W. Gentle, Nucl. Technol./Fusion 1, 479 (1981)]. Fluctuation amplitudes and correlation length scalings do not correspond to linear or quasilinear drift wave theory. Power-weighted root-mean-square (rms) wave number estimates are much lower (〈k¯θ〉rmsρs≤0.1, ρs=[miTe]1/2/eB) than quasilinear theoretical expectations (k¯⊥ρs∼0.3). Core results indicate strong turbulence with a wave number spread, Δk∼k¯ at fixed frequency f, consistent with strong turbulence predictions, while edge results can be considered consistent with weak turbulence. In between the core and edge (0.6≤r/a≤0.8) is a transition region. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871170
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  • 2
    Electronic Resource
    Electronic Resource
    An experimental counter-example to the local transport paradigm (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2292-2298 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The response of a tokamak discharge to a sharp drop in edge temperature differs significantly from that expected from typical local transport models in several important respects. Laser ablation of carbon induces large (ΔT/T≤70%), rapid (〈200 μs) electron temperature drops in the outermost region of the plasma, r/a≥0.9. This cold pulse proceeds through the outer plasma (r/a≥0.75), rapidly compared with power balance or sawtooth predictions. However, the pulse shrinks markedly thereafter, disappearing near r/a∼0.5. Within r/a∼0.3, the temperature rises promptly. The results are inconsistent with conventional local transport models; a nonlocal phenomenology, in which transport coefficients increase in the edge and decrease in the core, is suggested. The turbulence levels measured with a heavy ion beam probe increase near the edge but are unchanged in the core. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871252
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  • 3
    Electronic Resource
    Electronic Resource
    Broadband fluctuation wave number measurement technique using a heavy ion beam probe : Eighth topical conference on high-temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3058-3060 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The heavy ion beam probe (HIBP) measures localized density fluctuations in the plasma interior. These measurements can be used to calculate two point estimates of interior poloidal wave numbers. The results so far show wave numbers significantly lower than FIR scattering wave numbers and drift wave expectations. Experiments were performed on TEXT to look for possible sources of error in our wave number calculations. The HIBP effects that are considered the possible dominant error terms are finite sample volume size and path effect fluctuations as well as the possible existence of counter-propagating modes. An aperture experiment showed the presence of a finite sample volume effect, but not large enough to correct the measured wave numbers significantly. Simulations using HIBP data show that our processing techniques detect counter-propagating modes. Path effects are discussed. The error analysis so far shows the HIBP calculations to be accurate wave number measurements, but more study on path effects is needed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141726
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Plasma potential measurements on text-upgrade with a 2 MeV heavy ion beam probe (abstract)a) : 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. 316-316 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The plasma potential is measured in TEXT-upgrade tokamak by injection and detection of high energy heavy ions (thallium and cesium with a single charge) using a 2 MeV accelerator and a parallel plate energy analyzer. The change in beam energy, as it crosses the plasma, gives the local plasma potential at the measurement volume. Recent results of high energy beam operations are presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146396
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  • 6
    Electronic Resource
    Electronic Resource
    Path integral effects in heavy ion beam probe density measurements: A comparison of simulation results and experimental data (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1001-1009 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The heavy ion beam probe (HIBP) signal used to measure local density fluctuations in a plasma is also sensitive to modulation due to density fluctuations along the entire beam trajectory. A modulation model of the HIBP experiment on the Texas experimental tokamak (TEXT) is presented. The model includes profile information for equilibrium and fluctuating parameters, allows for differences in the radial and poloidal characteristics of the fluctuations, and uses realistic beam trajectories. It is shown that profile effects are important in understanding HIBP modulation and that modulation does not simply increase with line average density in TEXT. In addition, calculations of the modulation effects show that only the terms which correspond to in-phase signals at the two sample volumes are significant. Therefore, the modulation effects can be approximated with a real parameter. Under these assumptions, it is shown that only long correlation length, low wave number modes will contribute significantly to the corruption of the measured signal. The calculation of the modulation effects are consistent with the experiment. It is illustrated herein how the measured data can be used to set limits on the modulation signal without doing extensive model calculations. These limits show that there must be long wavelength fluctuations in the plasma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144169
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of beam-attenuation modulation on fluctuation measurements by heavy-ion beam probe (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2232-2240 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Beam-attenuation modulation arising from density fluctuations along the orbit of the heavy-ion beam probe (HIBP) in a plasma can distort the local amplitude, coherence, and phase derived from one- and two-point correlation measurements. Path-integral expressions for these effects are derived and applications to the TEXT tokamak are discussed. The work is part of an effort to account for previously reported wave-number data. However, the analysis is general and bears on any correlation measurement in turbulent media that depends on beam propagation or might otherwise be affected by spurious common-mode signals. In the HIBP case the effects depend critically on the ratio of the average fluctuation amplitude ñe along the beam path to the local ñe at the sample volume. Because the fluctuation amplitude is small in the core and rises sharply toward the plasma edge, the contamination effect is negligible in a radial zone near the edge but rises sharply to the interior of a critical radius. With increasing average plasma density n¯e the interior contamination increases strongly and the critical radius moves outward. The conclusion is that beam-modulation fluctuations affect the data but do not fully explain the disagreement with theoretical predictions of drift waves. The effects are expected to decrease with increasing beam energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143144
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  • 8
    Electronic Resource
    Electronic Resource
    High resolution electron cyclotron emission temperature profile and fluctuation diagnostic for Alcator C-Mod : 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. 1011-1013 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new second harmonic heterodyne electron cyclotron emission system with high spatial resolution (≤15 mm) and a large number of channels (32) for dense profile coverage will be installed on Alcator C-Mod. The system will provide detailed radial electron temperature profiles and core temperature fluctuation measurements. The collection system is composed of elliptical and parabolic mirrors coupled to two overmoded waveguides to provide high poloidal spatial resolution necessary for T˜e measurements. Four radiometer sections cover the frequency range of 234–306 GHz, coupled to four optimized intermediate frequency modules with eight channels of detectors, amplifiers, dividers, and filters providing the profile information. A separate filter arrangement allows for temperature fluctuation measurements utilizing correlation techniques. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149368
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  • 9
    Electronic Resource
    Electronic Resource
    Advances in heavy-ion beam probing (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1673-1675 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Recent applications of heavy-ion beam probes on such devices as the TEXT tokamak have shown the importance of increasing the capabilities of both the beam injection and detection systems. To this end we have investigated a new solid-state ion detector that will substantially improve spatial resolution. The application of the diagnostic technique on substantially larger devices will also require new electrostatic energy analyzer geometries, which are also under investigation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140129
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  • 10
    Electronic Resource
    Electronic Resource
    Core turbulence and transport studies on the Texas Experimental Tokamak (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2127-2135 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent experiments on the Texas Experimental Tokamak (TEXT) [Plasma Phys. Controlled Fusion 27, 1335 (1985)] have focused on identifying the drives and transport significance of the turbulence in the interior of discharges in the neo-Alcator confinement regime. Far-infrared (FIR) scattering consistently observes density fluctuations indicative of electron drift waves, i.e., ωk∼ωe*+kθvE, where vE≡−Er/B (the electron diamagnetic frequency Doppler-shifted by the E×B poloidal plasma rotation) and an amplitude that scales inversely with the density scale length Ln. Although consistent with scattering on the power-weighted frequency ω¯, heavy-ion beam probe (HIBP) data typically indicate k¯θρs〈0.1 such that ω¯(very-much-greater-than)ω¯e*+k¯θvE and n¯/ne(very-much-less-than)1/k¯θLn. Experiments with a modulated gas feed and/or electron-cyclotron resonance heating (ECRH) seem to rule out ∇Te as the turbulent drive, although little evidence for ∇ne is apparent either. In fact, the interior fluctuations seen by the HIBP seem to depend more on edge conditions than local gradients. The quasilinear fluxes due to dissipative trapped electrons are found to be sufficient to account for the equilibrium fluxes in the region of low collisionality (νe*(very-much-less-than)1) for a drift-wave spectrum (k¯θρs∼0.3), but not for the low wave numbers seen by the HIBP. While the estimates with k¯θρs∼0.3 predict the scaling of the electron energy flux over a range of discharge conditions with νe*(very-much-less-than)1, the model seems unable to predict the magnitude (or phase) of the perturbed particle flux during modulated gas feed experiments. In the outer regions of the plasma where νe*(approximately-greater-than)1, the calculated quasilinear fluxes are inadequate, even including untrapped particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860019
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