title: Detection of zonal flow spectra in DIII-D by a dual-channel Doppler backscattering system.
abstract: Doppler backscattering (DBS) has been successfully used to measure the E x B flow velocity and local intermediate wavenumber density fluctuation levels in the DIII-D tokamak. Depending on the launch angle and the frequency of the probing beam, the signal backscattered from the plasma cut-off layer is sensitive to density fluctuations at a specific perpendicular wavenumber (1 < or = k(perpendicular rho(s)) < or = 4). Due to the localization and high time resolution for poloidal flow measurements, DBS is well suited to detect stationary and time-dependent shear flows [zonal flows (ZFs)]. We present a novel scheme to measure ZF spectra using a dual-channel DBS system capable of simultaneously probing two minor radii separated by a distance of 0.2 cm < Delta r < 3 cm. Frequency spectra of geodesic acoustic modes and low frequency ZFs (f or = 10 kHz) have been obtained for 0.6 < r/a < 0.95.
authors.affiliation: UCLA Physics and Astronomy Department, Los Angeles, California 90095-1547, USA.
authors.forename: L
authors.initials: L
authors.lastname: Schmitz
authors.forename: G
authors.initials: G
authors.lastname: Wang
authors.forename: J C
authors.initials: JC
authors.lastname: Hillesheim
authors.forename: T L
authors.initials: TL
authors.lastname: Rhodes
authors.forename: W A
authors.initials: WA
authors.lastname: Peebles
authors.forename: A E
authors.initials: AE
authors.lastname: White
authors.forename: L
authors.initials: L
authors.lastname: Zeng
authors.forename: T A
authors.initials: TA
authors.lastname: Carter
authors.forename: W
authors.initials: W
authors.lastname: Solomon