Pressure Gradient Effects on Alfven Cascade Modes in Tokamaks

POSTER

Abstract

Alfven cascade modes are discrete shear Alfven eigenmodes localized at the radius of minimum of safety factor in tokamak plasmas with reserved shear q profiles [1]. The mode frequency is given by $\omega \sim (n- m/q_{min})V_A/R$ over most parameters, and transforms to the geodesic acoustic mode near rational field lines. The mode is seen in experiments, where the mode frequency sweeps up as q drops. Numerical results indicate that the plasma pressure gradient helps establish the mode [2], in contrast to a previous analytic prediction [3] that the pressure gradient term hinders mode establishment. here a modification of the analysis is developed to include a previously neglected interchange term due to the favorable average curvature of a tokamak. This is the key addition that is needed for the pressure gradient to be favorable for the establishment of a cascade mode, and thereby explain the numerical results. \newline [1] H. L. Berk et al., Phys. Rev. Lett. {\bf 87}, 185002 (2001). \newline [2] G. J. Kramer et al., Plasma Phys. Controlled Fusion {\bf 46}, L23 (2004). \newline [3] B. N. Breizman et al., Phys. Plasmas {\bf 12}, 112506 (2005).

Authors

  • G.Y. Fu

    Princeton Plasma Physics Laboratory

  • Barbara Jacak

    Texas A\&M University, University of Minnesota, Radiation Monitoring Devices, Inc., Livermore National Laboratory, MIT, Association EUTRATOM-CEA, CEA/DSM/DRFC, CEA Cadarache, 13108 St Paul Lez Durance France, University of Munich, Germany, LNS Catania, Italy, NASA Langley Research Center, Fermilab, University of Florida, Princeton Plasma Physics Laboratory, Princeton, NJ, U.S.A., Courant Institute, New York University, New York, U.S.A., Department of Physics, Harvard University, Department of Physics, McGill University, University of Illinois at Chicago, for the LIGO Scientific Collaboration, Stanford University, DESY, LPSC, Grenoble, France, University of Arizona, Cornell University, University of Wisconsin -- Milwaukee, Case Western Reserve University, Space Science Center and Department of Physics, University of New Hampshire, University of Chicago, Fermi National Accelerator Laboratory, University of Wisconsin, Lawrence Livermore National Laboratory, Princeton Plasma Physics Lab., ORNL, Politecnico diTorino, Max-Planck Institute for Plasma Physics, MIT-PSFC, UCLA Physics Department, Abastumani Astrophysical Observatory, A. Kazbegi 2a, Tbilisi 0160, Georgia, NYU, PPPL, Columbia University, UC-Davis, UCLA, UC-Irvine, Culham Science Centre, Massachusetts Institute of Technology, Fusion Research Center, Univ. of Texas at Austin, Institute for Fusion Studies, Univ. of Texas at Austin, Institute for Fusion Studies, Chalmers University of Technology, G\"{o}teborg, Sweden, Princeton Plasma Physics Lab, ANL, LLNL, Politecnico de Torino, Italy, UCSD, Lodestar Research Corp., Saclay, France, California Institute of Technology, NASA/GSFC, NRC, NASA/GSFC, Oslo, Mississippi State, Massachusetts-Lowell, NBI, Tennessee, Argonne National Lab, Florida State, US Naval Academy, Petersburg Nuclear Physics Institute, Dept. of Physics and Astronomy, Ohio Univ., Los Alamos National Laboratory, Ohio State University, University of Glasgow, Jet Propulsion Lab, Pasadena CA, U. of Minnesota, Minneapolis MN, Caltech, Pasadena CA, Washington U., St. Louis MO, NASA/GSFC, Greenbelt MD 20771, University of Michigan, Indiana University, Pennsylvania State University, Purdue University, CalTech, University of California, Berkeley and Lawrence Berkeley National Laboratory, University of Rochester, Washington University, St. Louis, University of Iowa, University of Kansas, University of Athens, Greece, Kent State University, Tenn Tech U., Oak Ridge Assoc. 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Colorado, CNR-IFP, Italy, Associazione Euratom-ENEA sulla Fusione, Italy, Office of Fusion Energy Sciences, US DoE, Fusion Research Center, Georgia Institute of Technology, Lawrence Livermore National Lab, Universidad Nacional de Cordoba, C.W. Post -- Long Island University, Brigham Young University, Louisiana State University, NSCL, Washington University in St. Louis, Cyclotron Institute Texas A\&M University, Cyclotron Institute, Texas A$\&$M University, College Station, TX 77843, Middle East Technical University/FNAL, INRNE-BAS/FNAL, Texas Tech University, FNAL, Cavendish Laboratory, University of Cambridge, UK, CIEMAT, Madrid, Spain, Center for Relativity, Department of Physics, University of Texas at Austin, Cyclotron Institute, Texas A\&M University, College Station, TX 77843, U. Sussex, Tulane U., NIST, U. 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Bonn, D-53115 Bonn, IIT, Chicago, IL 60616, Univ. of Michigan, Ann Arbor, MI 48109-1120, Duke University, SDSU, Racah Institute of Physics, Univ. of Trento, Gesellschaft f\"ur Schwerionenforschung, Bowling Green State Univ., Dept. of Chemistry, Indiana University, SUNY, Stony Brook