Intense geodesic acousticlike modes driven by suprathermal ions in a tokamak plasma |
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Authors: | Nazikian R Fu G Y Austin M E Berk H L Budny R V Gorelenkov N N Heidbrink W W Holcomb C T Kramer G J McKee G R Makowski M A Solomon W M Shafer M Strait E J Zeeland M A Van |
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Affiliation: | Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA. |
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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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