DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 211: Dependence of Zonal Flows on magnetic shear in internal transport barriers | ||
| Name: | Lothar Schmitz ( |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport Model Validation | Presentation time: | Requested | Co-Author(s): | G. Wang, T.L. Rhodes, E. Doyle, W.A. Peebles, A.E. White. G. McKee, M. Austin |
| Description: | Magnetic shear (in addition to ExB flow shear) is thought to control the amplitude of Zonal Flows and the radial turbulence correlation length in internal transport barriers. This process of turbulence self-regulation is predicted to control the resulting transport fluxes. A reduced radial correlation length for low-k fluctuations has been observed in DIII-D (T.L. Rhodes, Phys. Plasmas 9,2141,2003). Localized core measurements of Zonal flow structures by Doppler Reflectometry can now be attempted in DIII-D. The measurements proposed here rely on Doppler reflectometry in addition to BES, ECE and correlation ECE (CECE), and FIR scattering, to map out the transition from low-k dominated turbulence to TEM and/or ETG dominated turbulence which may occur as the transport barrier forms. The goal of the experiment is to map the evolution of poloidal flow components, <v pol> and v~ pol, and their correlation to the medium-k density fluctuation amplitude vs. magnetic shear. Since turbulence evolution is also determined by the <ExB> flow shear, discrimination of both effects is important. | ||
| Experimental Approach/Plan: | The Quiescent Double Barrier (QDB) discharge is suitable as an initial target for this work. It is stationary and relatively free of MHD activity in the barrier region. The barrier cover regions of negative and positive magnetic shear. Four-channel O-Mode Doppler reflectometry will be employed combined with BES to cover low and intermediate-k fluctuation spectra. Polodal flow spectra are extracted from these data. Profile reflectometry of the barrier region is crucial for density profile reconstruction. | ||
| Background: | A reduction of turbulence correlation length has been previously observed by reflectometry in QDB plasmas in DIII-D (T. Rhodes), and in ITB plasmas in JT60 (Nazikian et al, Phys. Rev. Lett. 94, 135002-1 (2005). Transient Zonal flow structures in the electron temperature profile have previously been seen in Internal Ion Transport Barriers triggered at rational-q surfaces. (M. Austin et al., Phys. Plasmas 13 082502 (2006).
The dependence of zonal flows on magnetic shear has been predicted theoretically (R. Waltz, 2006, Miyata et al., IAEA 2006,Kishimoto, 2004) | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | 4-channel Doppler and Profile refectometry, BES,
FIR-scattering, ECE and CECE, CER, MSE | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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