DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 102: Collisional damping of zonal flows/GAMs | ||
| Name: | George R. McKee ( |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport | Presentation time: | Requested | Co-Author(s): | D. Schlossberg, M. Shafer, K. Burrell, C. Holland, G. Tynan, L. Schmitz, A. White |
| Description: | Vary collisionality while examining zonal flow/GAM characteristics (amplitude, structure, etc.) to test expectations for ZF/GAM damping physics. | ||
| Experimental Approach/Plan: | Run plasmas were zonal flow/GAM (geodesic acoustic mode) features have been observed (moderate power, USN L-mode conditions) and vary the collisionality by adjusting the density and temperature, while maintaining profiles of other relevant dimensionless parameters approximately constant. The upper divertor pumps will be used to control density as much as possible. A combination of gas puffing, pumping, neutral beam power and ECH will be used to adjust density-temperature to vary the collisionality.
BES is being expanded and reconfigured during this coming 2008 run-period to allow for wider field and greater poloidal-extent measurements. This new capability will be especially valuable for these studies of zonal flows, which are predicted to be m=0 structures. It will allow for greater confidence in identifying the poloidal structure of these flows. | ||
| Background: | Zonal flows (including GAMs) are expected to be collisionally damped by ion-ion collisions. This is founded in the theoretical understanding of zonal flows and has been borne out in simulations. Damping of zonal flows can in turn reduce zonal flow shearing, resulting in higher turbulence and associated transport levels. GAMs have been robustly observed near the outer regions of L-mode discharges on DIII-D using the multipoint BES system, and recent measurements with the upgraded, high-sensitivity BES show features of the lower-frequency residual, or Zero-Mean-Frequency zonal flow deeper in the core. Thus we have the diagnostic capability to examine zonal flows and their characteristics. Experimental determination of the role of collisionality on zonal flows will help validate turbulence models and thereby increase our overall physics understanding as well as predictive capability.
This data set would allow simultaneous measurement of zonal flows/GAMs as well as the ambient turbulence as a function of collisionality. Simulations of these plasmas with GYRO and a comparison of the resulting turbulence/zonal flow characteristics with measurements will help challenge and validate the code. An added benefit to this experiment will be to obtain measurements of general turbulence characteristics as a function of collisionality, thus continuing a program of nondimensional scaling of turbulence characteristics. | ||
| Resource Requirements: | Most NB sources | ||
| Diagnostic Requirements: | All fluctuation and profile diagnostics,esp. BES, Doppler reflectometer, CECE | ||
| Analysis Requirements: | Fluctuation/TDE analysis | ||
| Other Requirements: | -- | ||
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