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2007

  1. A Systematic Method for Verification and Validation of Gyrokinetic Microstability Code (440kB pdf) - R. V. Bravenec, J. Candy, G. M. Staebler, R. E. Waltz, W. Dorland, G. W. Hammett, Presented at TTF07

2006

  1. Studies of H-mode Pedestal Width through Gyrokinetic Microstability Analysis of the Top of the Pedestal (2.4MB pdf) - R. V. Bravenec, W. L. Rowan, I. O. Bespamyatnov, R. J. Groebner, T. Osborne, J. Candy, G. M. Staebler, M. Greenwald, W. Dorland, Presented at TTF06
    A yet unresolved puzzle concerning the H-mode pedestal is what determines the width of the steep-gradient region. Unfortunately, gyrokinetic microstability analysis is not valid in this region because the local ballooning mode approximation is violated, ∂f/f is no longer small, etc. However, a paradigm recently put forward posits that the steep-gradient region extends into the core only as far as the ExB shearing rate can overwhelm the maximum linear growth rate of the turbulence. We take this position and analyze the region just at the top of the pedestal, i.e., where the gradients are shallow enough so that the gyrokinetic treatment is valid, hoping to glean insight into the character of the turbulence. In particular, we employ the GS2 code,1 which can use actual numerical equilibria, to analyze the microstability of this region as close to the steep-gradient region as possible. We then compare the maximum linear growth rates to the ExB shearing rates as determined from measurements. This is performed for two disparate H-mode plasmas: a particularly well diagnosed low-density DIII-D ELMy H-mode plasma and a high-density Alcator C-Mod enhanced-Dalpha H-mode plasma.
    Supported by USDOE under grants DE-FG03-97ER54415, DE-FG03-96ER54373, and DE- FG02-93ER54197, and Coop. Agreements DE-FC02-04ER54698 and DE-FC02-99-ER54512.
    1 F. Jenko, W. Dorland, M. Kotschenreuther, and B. N. Rogers, Phys. Plasmas 7, 1904 (2000) and refs. therein.

  2. Shear Stabilization of Turbulence in Tokamaks: An Application for Line Shape Analysis of Impurity Spectra Excited by Interaction with a Hydrogen Neutral Beam - (1.7MB PDF) - William L. Rowan, I. O. Bespamyatnov, and R. V. Bravenec
    To be published in Proceedings of the 18th International Conference on Spectral Lines Shapes
    The edge of a tokamak plasma can be characterized by regions of sharp gradients which indicate good plasma confinement by the magnetic fields. Unfortunately, these gradientsand the regions of high confinement do not extend very far into the plasma. Here we will report our experiments which are intended to understand why the region of good confinement does not extend further into the plasma. Plasma parameters which are critical to interpretation of the experiments are derived from line shape analysis of impurity spectra. To support this interpretation, an accurate model for the line shape is needed and will be presented here. The model takes into accounts effects of magnetic field, details of the excited state of the beam, motion of the emitting ion, and blends of interfering spectra. The methods for extraction of the useful spectral parameters, intensity, spectral width spectral shift, and uncertainties in each, will be described.

  3. Effects of Neutral-Beam Excited States on Charge-Exchange Emission Cross Sections (540kB PDF file) I. O. Bespamyatnov and W. L. Rowan, R. S. Granetz and D. F. Beals

    Charge-exchange recombination spectroscopy (CXRS) can be used as a diagnostic for local densities of fully stripped impurities. For example, impurity profiles are valuable for transport studies. A major impediment to analysis is the availability of cross sections which relate the observed spectroscopic emission to the impurity densities. In this work, this impediment is removed for boron ions. Emission cross sections for B+4 states excited by charge exchange between beams of neutrals and fully stripped B+5 impurities in high density plasmas are computed for beams with multiple energy components. We show that even the low-energy neutral beam components make significant contributions to the emission for high-density plasmas which are commonly generated in the laboratory. Excited states as high as n=3 are important. This implies that a detailed description of the beam components including density, excited state population, and penetration is required for prediction of intensities of spectral lines excited by diagnostic neutral beams in high- density plasmas. Plasma experiments performed on the Alcator C-Mod tokamak will be described which clearly show the efficacy of our analysis method. This technique can be extended to species other than boron.

2005

  1. One Experimentalist’s View on Gyrokinetic Code Verification and Validation, (142kB PDF file) R. V. Bravenec, Presentation at TTF05.

  2. One Experimentalist's View on Gyrokinetic Code Verification and Validation, (2.5GB PDF file) R. V. Bravenec, D. Ross , J. Candy, R. Waltz, W. Dorland, Poster at TTF05

2004

  1. BEAM EMISSION SPECTROSCOPY ON THE ALCATOR C-MOD TOKAMAK - Matthew Sampsell, Dissertation Presented to the Faculty of the Graduate School of the University of Texas at Austin in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy.
  2. Electron Cyclotron Emission Measurements of Coherent and Broadband Density Fluctuations in the Alcator C-Mod Tokamak (5.2MB) -Alan Gene Lynn, B.S..
  3. Electron Cyclotron Emission (ECE) as a Density Fluctuation Diagnostic (400kB) - A.G. Lynn, P.E. Phillips, FRC, UT, A. Hubbard, PSFC, MIT.
  4. Interpretation of Neutral Beam Emission Spectras the Beam-Component Density Distribution (600kB) - William L. Rowan, R. V. Bravenec, M. B. Sampsell, Fusion Research Center, The University of Texas at Austin, Austin, TX 78712, R. S. Granetz, Plasma Science and Fusion Center, MIT, Cambridge, MA 02139.
  5. Neutral Beam Diagnostics for the HT-7 Tokamak (400kB) - L.Q. Hu, William L. Rowan, B.N. Wan1, C.D. Hu, H. He, B.H. Liu, K. Gentle, and HT-7 DNB Team
  6. Improved spatial resolution for the DIII-D ECE radiometer (1MB) - M.E. Austin,University of Texas, R.F. Ellis, University of Maryland
  7. Attainment of Arc Parameters Required for Full-CurrentOperation of the Diagnostic Neutral Beam (2.8MB pdf), W.L. Rowan, Huang He, C.D. Hu, et al, FRC Report 532.

2003

  1. Observations of core modes during RF-generated internal transport barriers in Alcator C-Mod (560kB) - A G Lynn1, P E Phillips1, A E Hubbard2 and S J Wukitch2
  2. Comparison of Two Ionization Approaches for the VASIMR Engine (1MB pdf) - Evangelos Anastasios Meintanis, B., Thesis .
  3. Characterization of the Resonant Electromagnetic Mode in Helicon Discharges (1.5MB pdf) - Martin Ivanov Panevsky, DISSERTATION

2002

  1. REVIEW OF GYROKINETIC SIMULATIONS AND COMPARISON WITH EXPERIMENT - David W. Ross, TTF, Annapolis, April 5, 2002

  2. Comparison of turbulence simulation with experimentÐÐissues and discussion - David W. Ross, Sherwood, Rochester, April 22, 2002.

2001

  1. Comparing Turbulence Simulation with Experiment, ,D. W. Ross, W. Dorland, and D. Mikkelsen, Proceedings of the Transport Task Force Workshop, Fairbanks, Alaska, (2001).

  2. Sawteeth heat pulse propagation in Alcator C-Mod (pdf)- A. Lynn, R. Chatterjee, P.E. Phillips, K.W. Gentle, R. V. Bravenec, Fusion Research Center, The University of Texas at Austin, C. Watts, Auburn University, Y. In, University of Idaho, A. Hubbard, M. Greenwald, PSFC, MIT - presented at TTF conference.

  3. Floating Potentials in the Vicinity of Biased Flush-Mounted Probes - D. L. Winslow, B. LaBombard, January 30, 2001

2000

  1. Effects of Flush-Mounted Probe Bias on Local Turbulent Fluctuations - D.L. Winslow, B. LaBombard - PSI conference paper.
  2. CXRS on Alcator C-Mod - E. C. Eisner and William L. Rowan, Fusion Research Center, The University of Texas at Austin
  3. First Results from Beam-Emission Spectroscopy on Alcator C-Mod - Presented at TTF 2000 - R. V. BRAVENEC, M. B. SAMPSELL, W. L. ROWAN, E. C. EISNER, D. M. PATTERSON, Fusion Research Center, The University of Texas at Austin, N. L. BRETZ, Princeton Plasma Physics Laboratory, A. E. HUBBARD, J. H. IRBY, E. S. MARMAR, J. L. TERRY, MIT Plasma Science and Fusion Center.
  4. Comparing Turbulence Simulation with Experiment in DIII-D. - David W. Ross and Ronald V. Bravenec Fusion Research Center, The University of Texas at Austin, William Dorland, The University of Maryland, Michael A. Beer and G. W. Hammett, Princeton Plasma Physics Laboratory, George R. McKee, The University of Wisconsin, Madison, Masanori Murakami, General Atomics.

1999

  1. TTF Presentation by D. Ross
    The sensitivity of fluctuation levels and transport fluxes to local plasma parameters and gradients is investigated using the PPPL/IFS nonlinear gyrofluid simulation code.
  2. Investigation of scrape-off layer up-down asymmetries in diverted plasmas in TEXT-Upgrade - X. Bonnin and William L. Rowan - To be published in Nuclear Fusion.
 1998
  1. Comparisons of Measurements and Gyrofluid Simulations of Turbulence in DIII-D R. V. Bravenec, D. W. Ross, G. R. McKee,1 R. J. Fonck,1 M. Kotschenreuther, W. Dorland, M. A. Beer, G. W. Hammett, M. Austin, D. M. Patterson, W. L. Rowan, A. J. Wootton, K. H. Burrell, J. C. DeBoo, C. M. Greenfield

 1997

  1. The q-Diagnostic on TEXT-U - (3.4MB)Lokesh Kumar Duraiappah - Dissertation

 1991

  1. QUASILINEAR TRANSPORT INFERRED FROM DENSITY FLUCTUATION SPECTRA (2.5MB pdf), R.V. BRAVENEC, DAVID W. ROSS, P.M. SCHOCH, D.L. BROWER, J.W. HEARD, R.L. HICKOK, P.W. TERRY, A. J. WOOTTON, X.Z. YANG, Nucl. Fusion 31, 687 (1991).