DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 113: Understanding low density limit for L-H transition power threshold | ||
| Name: | Guiding Wang ( |
Affiliation: | University of California, Los Angeles |
| Research Area: | General IP | Presentation time: | Not requested | Co-Author(s): | J.C. DeBoo, K.H. Burrell, J. Snipes |
| Description: | The purpose is to understand the mechanism and explore the scaling of low density limit (namely the density at minimum power threshold) with Bt and Ip for L-H transition power threshold. This has been identified as a potential issue for ITER. This is an ITPA joint experiment (CDB-10). | ||
| Experimental Approach/Plan: | Perform density scan of the L-H power threshold at one set of plasma parameters until the density at minimum power threshold can be identified. Scan Bt and Ip and do the similar density scans to achieve the Bt and Ip dependence of this density limit. Collect full set of edge profile and fluctuation data. | ||
| Background: | ITER is planned to access H-mode in a low density (0.5*10^20 m^-3, ~0.4*n_GW) L-mode target. However, low density limit for L-H transition power threshold has been observed in major tokamaks including DIII-D, namely power threshold increases at densities lower than a certain density. So it is crucial to find out if this ITER L-mode target density is below or above the low density limit for ITER in order to predict required power for H-mode access (The scaling law of power threshold in the ITPA power threshold database is defined by excluding low densities). Previous experiments on several major tokamaks including DIII-D showed a low density limit ~0.2-0.3*10^20 m^-3 (except for C-mod at 1*10^20 m^-3), but ~0.2-0.3 if normalized to the Greenwald density limit. So it is desired to find out the scaling of low density limit with Bt and Ip. There is no theory available to understand low density limit for power threshold. Edge fluctuation data could be helpful to understanding the mechanism. Recent experiment on C-mod showed no dependence on Ip. | ||
| Resource Requirements: | All co- and counter-beams. | ||
| Diagnostic Requirements: | fluctuation diagnostics | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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