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  • 1995-1999  (29)
  • 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
    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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  • 4
    Electronic Resource
    Electronic Resource
    Current density profile measurement on the Texas Experimental Tokamak using a heavy ion beam probe (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 3828-3834 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For the first time, a heavy ion beam probe has been used to measure the poloidal magnetic flux in a tokamak. In this measurement, first proposed over 20 years ago, the toroidal displacement of the heavy ion beam probe particles is caused by the force of the poloidal magnetic field on the ion beam probe particles. In a nearly toroidally symmetric device such as the Texas Experimental Tokamak, the toroidal position of the ions at the detector consists of a part proportional to the poloidal magnetic flux at the sample volume and an integrated contribution of the poloidal magnetic flux along the trajectory. The local part in the relation between beam position and magnetic flux is used as a correction term in an iterative algorithm that calculates the poloidal magnetic flux. The q profile and the current density profile can be derived from the measured poloidal flux. Errors of the measurement can be due to uncertainties in the analyzer position and also in the knowledge of the location of the sample volume. Also uncertainties in the plasma current and position contribute to the error of the poloidal flux measurement. It is essential to know the magnetic field outside the plasma. The calculation of the outside field is difficult due to the presence of the iron core. The error in the measurement of the poloidal flux is on the order of 1%. The current profiles and q profiles were measured for discharges with on axis and off axis electron cyclotron resonance heating (ECRH), and with impurity injection. As expected, all current profiles peak in the center. With central ECRH, the measured current profiles are consistent with a prediction based on Spitzer resistivity and the measured electron temperature profile. In these plasmas, the safety factor has a central value of qc=0.95±0.1 and near the center of the plasma, the poloidal flux is observed to increase with time. The current profiles for off axis ECRH exhibit a larger current density in the wings of the distribution than comparable centrally heated ECRH plasmas. Results from plasmas with impurity injection yield qc=0.6 which is significantly lower than expected since these plasmas have m=2 activity. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149185
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  • 5
    Electronic Resource
    Electronic Resource
    Design of improved electric potential fluctuation detector for 2 MeV heavy ion beam probe on TEXT (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. 837-837 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The present detector system used for the TEXT heavy ion beam probe (HIBP) is not sensitive to potential fluctuations of magnitude below 10−5×Vacc where Vacc is the accelerator voltage. With the upgrade of the TEXT HIBP to 2 MeV, the minimum detectable fluctuation is on the order of 10 V under optimum conditions. A new detector system has been proposed, and a proof-of-concept experiment has indicated that it should be sensitive to fluctuations on the order of 1 V. The new system separates the ion beam entering the energy analyzer into ten smaller beams. The fluctuations in each smaller beam are measured individually, effectively increasing the signal by a factor of 10 without increasing detector noise. A version of the new detector system is presented that is designed specifically for the high-energy analyzer of the 2 MeV TEXT HIBP. In addition to the improved detector set, this design includes a standard detector set for side-by-side comparison, as well as for measuring other plasma parameters. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146240
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  • 6
    Electronic Resource
    Electronic Resource
    Computer control and data acquisition of the heavy ion beam probe (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. 315-315 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The heavy ion beam probe (HIBP) on TEXT-upgrade and the vertical test stand (VTS) at Rensselaer are to be operated from a virtual control panel using a graphical language interfacea). The system will monitor and control over eighty signals, as well as acquire data using mouse and keyboard inputs. The computer interface utilizes a DEC 5000/240 workstation, two color monitors, SCSI to fiber optic link, and CAMAC crate. Long term goals include remote experimental monitoring and control, and feedback control. The status and visuals of the computer control system and results of implementation on the VTS will be presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146394
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of the electric field and gain of the 2 MeV energy analyzer (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. 315-315 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Accurate determination of plasma potentials in the TEXT-upgrade tokamak using the 2 MeV heavy ion beam probe requires a good understanding of detector characteristics. The detector utilized is a parallel plate electrostatic energy analyzer. A figure of merit for this analyzer is the gain, GA, which is defined as the ratio of the potential of the incident ions to the potential applied to the analyzer anode. Tests are in progress on the vertical test stand at Rensselaera) to characterize the dependence of gain on radial entrance angle, toroidal entrance angle, and toroidal position of the ion beam. Results will be used to assist with in situ calibration on the TEXT-upgrade facility. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146395
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Poloidal magnetic flux measurement on TEXT using a heavy ion beam probe (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. 316-316 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The displacement out of the toroidal plane of the heavy ions of the beam probe diagnostic is caused by forces due to the poloidal magnetic field. In a nearly toroidally symmetric device such as the TEXT tokamak, the toroidal position of the ions at the detector consists of a part proportional to the poloidal magnetic flux at the sample volume and an integrated contribution of the poloidal magnetic flux along the trajectory. The local part in the relation between beam position and magnetic flux is used in an iterative algorithm that calculates the trajectories in the magnetic field of the tokamak. The q profile can be derived from the measured poloidal flux. Errors of the measurements can be due to uncertainties in the analyzer position and also in the knowledge of the location of the sample volume. Also, uncertainties in the plasma current and position contribute to the error in the q measurement. It is essential to know the magnetic field outside the plasma. The calculation of the outside field is difficult due to the presence of the iron core and is still a matter of investigation, since it has a strong effect on the measurement. A description of the measurement and an error analysis is presented with examples of q profiles for discharges with ECH heating and strong magnetic fluctuations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146397
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  • 10
    Electronic Resource
    Electronic Resource
    Sweep system design for a heavy ion beam probe on 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. 967-970 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The sweep system for the heavy ion beam probe on the Madison Symmetric Torus (MST) is described. The two components of the system are the primary sweep optics and secondary collimation plates. Key issues in the sweep system design are the small entrance and exit ports available on MST, the significant toroidal beam motion induced by the strong poloidal magnetic field, and the excessive current loading due to plasma and ultraviolet (UV). The design accommodates these issues using a crossover sweep plate design in two dimensions for the primary beam as well as two dimensional sweeping on the secondary beam. The primary beam sweep design results in a sweep range of ±20° in one direction and ±5° in the perpendicular direction. The secondary beam sweep design results in entrance angles to the energy analyzer of 〈3° in radial and ∼0° in toroidal directions. The procedure for calculating sweep performance including fringe fields, a system for active trajectory control, and initial experiments on plasma and UV loading are also discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149418
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