Speaker
Mr
Shigeyuki Kubota
(USA)
Description
The measurement of radially extended meso-scale structures such as zonal flows and streamers, as well as the underlying microinstabilities driving them, is critical for under-standing turbulence-driven transport in plasma devices [1]. In particular, the shape and evolution of the radial wavenumber spectrum indicate details of the nonlinear spectral energy transfer [2], the spreading of turbulence [3], as well as the formation of transport barriers [4]. In the National Spherical Torus Experiment (NSTX), the FMCW backscattering diagnostic [5] is used to probe the turbulence radial wavenumber spectrum (k_r =0-22 cm^-1) across the outboard minor radius near the L- to H-mode transition in Ohmic discharges. During the L-mode phase, a broad spectral component (k_r~2-10 cm^-1) extends over a significant portion of the edge-core from R=120 to 155 cm (rho=0.4-0.95). At the L-H transition, turbulence is quenched across the measurable k_r range at the ETB location, where the radial correlation length drops from ~1.5 to 0.5 cm. The k_r spectrum away from the ETB location is modified on a time scale of tens of microseconds, indicating that nonlocal turbulence dynamics are playing a strong role. Close to the L-H transition, oscillations in the density gradient and edge turbulence quenching become highly correlated. These oscillations are also present in Ohmic discharges without an L-H transition, but are far less frequent. Similar behavior is also seen near the L-H transition in NB-heated discharges.
*Work supported by U.S. DOE Contracts DE-FG02-99-ER54527 and DE-AC02-09CH11466.
[1] A. Fujisawa et al., Plasma Phys. Control. Fusion 53, 124015 (2011).
[2] J. Li and Y. Kishimoto, Phys. Plasmas 17, 072304 (2010).
[3] T.S. Hahm et al., Plasma Phys. Control. Fusion 46, A323 (2004).
[4] W.X. Wang et al., Phys. Plasmas 14, 072306 (2007).
[5] S. Kubota et al., 53rd Meeting of the APS Division of Plasma Physics, B04.00003 (2012).
Country or International Organization of Primary Author
USA
Primary author
Mr
Shigeyuki Kubota
(USA)
Co-authors
Dr
Ahmed Diallo
(PPPL)
Dr
Benoit P. LeBlanc
(PPPL)
Dr
Charles E. Bush
(ORNL)
Dr
Jong-Kyu Park
(Princeton Plasma Physics Laboratory)
Dr
Neal Crocker
(University of California Los Angeles)
Dr
R.E. Bell
(PPPL)
Dr
Rajesh Maingi
(Oak Ridge National Laboratory)
Dr
Ricardo J. Maqueda
(Nova Photonics)
Dr
Roger Raman
(University of Washington)
Dr
Stanley Kaye
(Princeton Plasma Physics Laboratory, Princeton University, Princeton NJ, 08543 USA)
Dr
Stewart J. Zweben
(PPPL)
Dr
William A. Peebles
(UCLA)
Dr
Yang Ren
(Princeton Plasma Physics Laboratory)
