Detection of zonal flow spectra in DIII-D by a dual-channel Doppler backscattering system.
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.
Schmitz
L
L
UCLA Physics and Astronomy Department, Los Angeles, California 90095-1547, USA.
Wang
G
G
Hillesheim
J C
JC
Rhodes
T L
TL
Peebles
W A
WA
White
A E
AE
Zeng
L
L
Carter
T A
TA
Solomon
W
W