DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 111: H-mode operation near the threshold power | ||
| Name: | Guiding Wang ( |
Affiliation: | University of California, Los Angeles |
| Research Area: | ITER Demonstration Discharges | Presentation time: | Requested | Co-Author(s): | J.C. DeBoo |
| Description: | The purpose is to characterize the H-mode access in ITER-like L-mode target plasma in DIII-D (ne~0.4*n_GW, ITER shape, q_95 ~3-3.5, low rotation) at different input power levels (PLTH/P_th~1.1, 1.2, 1.3, 1.5, etc). This is an ITPA joint experiment (CDB-11). | ||
| Experimental Approach/Plan: | After establishing ITER-like L-mode Deuterium target plasma at ne~0.4*n_GW and H-mode threshold power being found with power ramp, vary input power shot-to-shot but at a fixed level during each shot (PLTH~1.1, 1.2, 1.3, 1.5 x P_th). Establish new equilibrium condition. If new ne level is below 0.8*n_GW, then gas puff to achieve 0.8*n_GW to see if H-L transition occurs. Characterize ELMs and confinement properties after the L-H transition. If good confinement in the H-mode phase is not achieved, raise input power further. Repeat above process at 2 or 3 collisionality levels. | ||
| Background: | Due to power limitations, ITER will likely need to access H-mode at a low density (0.5*10^20 m^-3, ~0.4*n_GW) with input power close to H-mode power threshold then achieve their target flattop density of 1*10^20 m^-3 without more input power. So it is important to have dedicated experiments to demonstrate/document this scenario. Recent relevant results in different machines provide mixed information. For example on ASDEX database analysis shows that at input power close to threshold power, good confinement can be achieved with Type-I ELMs at low enough collisionality (<1), but at high collisionality Type-III ELMs appear and confinement is ~ 20% worse. On JET, when input power is close to threshold power, Type-III ELMs always dominate and confinement is 10-20% worse than H~1 except at low densities. Typically PLTH~(1.3-2.5)*P_th is needed to achieve Type-I ELMs with good confinement depending on conditions. On DIII-D, when input power is close to threshold power, normally Type-III ELMs appear, and confinement is normally poor at low densities but could reach higher H if edge pressure gradient increases at high density. | ||
| Resource Requirements: | All co- and counter-beams. | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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