DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 159: Turbulence dynamics of integer q surfaces in near-sationary NCS discharges w/ off-axis ECCD | ||
| Name: | Morgan Shafer ( |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport | Presentation time: | Requested | Co-Author(s): | G. McKee, D. Schlossberg, M. Austin, K. Burrell |
| Description: | Develop stationary or slowly evolving NCS L-Mode discharges to examine zonal flows and turbulence dynamics in the vicinity of low-order rational q surfaces at zero magnetic shear to examine ITB formation. Use ECCD to drive off-axis current to slow evolution in near-stationary L-Mode NCS discharges. This will allow for far more detailed examination of the evolution and provide good statistics (long, stationary windows for averaging) for high frequency velocity measurements with BES. | ||
| Experimental Approach/Plan: | Necessary discharge conditions: L-Mode, NCS, low density. Various ECCD deposition locations will be utilized, ideally rho(qmin)>0.5., with qmin=2. Application of the ECCD will slow down the evolution of qmin to provide near-stationary q profiles. Two cases of toroidal rotation, 2 co- beams, 1 co- and 1 counter- beams. Previous experiments have shown RSAE modes are less excited at lower rotation, which improves velocity measurements from BES. Repeat scans of the BES array will be needed, given sufficient discharge conditions. MSE data is necessary. A specialized BES channel configuration with 4x12 to 4x16 poloidally offset channels maybe used for extended poloidal coverage for ZF studies. | ||
| Background: | Previous measurements with BES have shown rapid changes in turbulence and turbulence flows near low-order rational q surfaces in NCS discharges. There have similarly been clear simulation and theory predictions for zonal flows or zonal flow-like structures (convective cells) tied to integer q surfaces with weak or no magnetic shear. Higher frequency zonal flows were unresolvable given the rapidly evolving conditions and the long averaging windows required for the measurement. Previous attempts to trigger ITBs with integer values of qmin have used an early NBI to create a temporary off-axis current peak, which moves into the core as the discharge evolves. This resulted in non-stationary NCS q-profiles. | ||
| Resource Requirements: | Neutral Beams, ECCD | ||
| Diagnostic Requirements: | BES, MSE, CER, ECE | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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