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Intense geodesic acousticlike modes driven by suprathermal ions in a tokamak plasma.

  • Author(s): Nazikian, R
  • Fu, GY
  • Austin, ME
  • Berk, HL
  • Budny, RV
  • Gorelenkov, NN
  • Heidbrink, WW
  • Holcomb, CT
  • Kramer, GJ
  • McKee, GR
  • Makowski, MA
  • Solomon, WM
  • Shafer, M
  • Strait, EJ
  • Zeeland, MA Van
  • et al.
Abstract

Intense axisymmetric oscillations driven by suprathermal ions injected in the direction counter to the toroidal plasma current are observed in the DIII-D tokamak. The modes appear at nearly half the ideal geodesic acoustic mode frequency, in plasmas with comparable electron and ion temperatures and elevated magnetic safety factor (q_{min}>or=2). Strong bursting and frequency chirping are observed, concomitant with large (10%-15%) drops in the neutron emission. Large electron density fluctuations (n[over ]_{e}/n_{e} approximately 1.5%) are observed with no detectable electron temperature fluctuations, confirming a dominant compressional contribution to the pressure perturbation as predicted by kinetic theory. The observed mode frequency is consistent with a recent theoretical prediction for the energetic-particle-driven geodesic acoustic mode.

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