Low-q resonances, transport barriers, and secondary electrostatic convective cells
- Center for Astrophysics and Space Sciences and Department of Physics, University of California at San Diego, La Jolla, California 92093-0424 (United States)
Recent experimental observations have suggested key characteristics of internal transport barrier (ITB) formation near low-q surfaces in off-axis minimum-q (OAMq) discharges. These observations identify mean profile flattening localized to the low-q surface as a transition precursor in the absence of observable magnetic field perturbations. This observation suggests an electrostatic model of ITB formation which accounts for strong transport in the immediate vicinity of the low-q surface, as well as the formation of an ITB nearby the surface. Here, a low-m electrostatic convective cell driven by modulational instability of the background drift wave turbulence is discussed in the context of ITB formation near low-q resonances in OAMq discharges. Unlike pure m=n=0 zonal flows, convective cells are capable of intense mixing localized around low-q resonant surfaces, thus relaxing {nabla}T and {nabla}n profiles at the k{center_dot}B=0 resonance. However, nearby, but off the low-q resonant surface the magnitude of convective cell shear is maximal, providing an effective means of triggering a transport barrier there. Field line bending coupled with collisional viscosity are found to strongly damp the intensity of the vortical flows except in the case of weak magnetic shear. Furthermore, collisionless nonlinear saturation mechanisms such as nonlinear wave trapping are largely circumvented due to the strong mixing of the convective cell. This suggests that low-m convective cells may play a key role in the regulation of turbulent transport near low-q resonances for OAMq discharges.
- OSTI ID:
- 21069889
- Journal Information:
- Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 11 Vol. 14; ISSN PHPAEN; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Production of internal transport barriers via self-generated mean flows in Alcator C-Mod
Core barrier formation near integer q surfaces in DIII-D
Behavior of electron and ion transport in discharges with an internal transport barrier in the DIII-D tokamak
Journal Article
·
Tue May 15 00:00:00 EDT 2012
· Physics of Plasmas
·
OSTI ID:22072391
Core barrier formation near integer q surfaces in DIII-D
Journal Article
·
Tue Aug 15 00:00:00 EDT 2006
· Physics of Plasmas
·
OSTI ID:20860188
Behavior of electron and ion transport in discharges with an internal transport barrier in the DIII-D tokamak
Conference
·
Mon Nov 30 23:00:00 EST 1998
·
OSTI ID:291189