title: Intense geodesic acousticlike modes driven by suprathermal ions in a tokamak plasma.
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.
authors.affiliation: Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA.
authors.forename: R
authors.initials: R
authors.lastname: Nazikian
authors.forename: G Y
authors.initials: GY
authors.lastname: Fu
authors.forename: M E
authors.initials: ME
authors.lastname: Austin
authors.forename: H L
authors.initials: HL
authors.lastname: Berk
authors.forename: R V
authors.initials: RV
authors.lastname: Budny
authors.forename: N N
authors.initials: NN
authors.lastname: Gorelenkov
authors.forename: W W
authors.initials: WW
authors.lastname: Heidbrink
authors.forename: C T
authors.initials: CT
authors.lastname: Holcomb
authors.forename: G J
authors.initials: GJ
authors.lastname: Kramer
authors.forename: G R
authors.initials: GR
authors.lastname: McKee
authors.forename: M A
authors.initials: MA
authors.lastname: Makowski
authors.forename: W M
authors.initials: WM
authors.lastname: Solomon
authors.forename: M
authors.initials: M
authors.lastname: Shafer
authors.forename: E J
authors.initials: EJ
authors.lastname: Strait
authors.forename: M A Van
authors.initials: MA
authors.lastname: Zeeland