DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 242: Beta Scaling of turbulence and transport in low-rotation H-Mode Plasmas | ||
| Name: | George R. McKee ( |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport Model Validation | Presentation time: | Requested | Co-Author(s): | C. Petty, C. Holland, T. Luce, D. Schlossberg, M. Shafer |
| Description: | The plasma pressure plays a key role in both driving and stabilizing turbulence. This experiments seeks to vary beta systematically in a set of dimensionally-matched H-mode discharges (similar to those run by C. Petty in 2003) and examine the turbulence characteristics to see if they scale in a manner consistent with theory/simulation and observed transport scaling. | ||
| Experimental Approach/Plan: | Develop low to moderate rotation H-mode discharges at the highest feasible beta_N, then step down beta_N (from perhaps near 3 to about 1) while maintaining other dimensionless parameter nearly constant. Toroidal field and current will be varied by perhaps 25% in this process as density and beam power are scaled more strongly so as to maintain dimensionless parameters roughly constant. At each condition, several repeat discharges will be required to acquire the necessary spatial scan with BES. Also, 150L should be run steady while 150R is off.
All fluctuation diagnostics will be utilized to obtain as comprehensive a set of turbulence characteristics as possible. | ||
| Background: | Experiments and simulations have shown the importance and impact of beta scaling on turbulence and transport. Generallly, as plasma pressure increases, one might expect the turbulence drive to likewise increase. At some beta, alpha-stabilization kicks in and begins to stabilize turbulence. At yet higher beta, electromagnetic instabilities such as kinetic ballooning modes might be driven unstable. For purely electrostatic ExB turbulence, beta does not play a direct role. H-mode beta scaling studies on D3D showed that transport and confinement time vary little with beta (Petty, PoP, 2004), consistent with transport dominated by electrostatic turbulence.
The upgraded BES system provides significantly enhanced sensitivity to small-amplitude fluctuations and has demonstrated capability to measure turbulence in the core of H-mode discharges. We will utilize this capability to monitor turbulence characteristics as beta is varied while other relevant dimensionless parameters are held nearly constant. A similar experiment was performed in hybrid discharges in 2007, however the beta range was quite limited due to ELM-free operation at low beta, and NTMs at higher beta. Furthermore the discharges were not very reproducible which limited the ability to obtain comprehensive measurements with fluctuation diagnostics. The goal will be to utilize the scaling of turbulence characteristics to compare with and help validate models and nonlinear simulations (TGLF, GYRO, etc.). | ||
| Resource Requirements: | All NB sources | ||
| Diagnostic Requirements: | Full Profile and fluctuation diagnostics | ||
| Analysis Requirements: | Lots... | ||
| Other Requirements: | -- | ||
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