DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 394: High energy confinement, low density Type III discharges and study of Type III - Type I transition | ||
| Name: | Tom Osborne ( |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics | Presentation time: | Not requested | Co-Author(s): | P. Snyder, A. Leonard, J. Yu, J. Boedo, R. Moyer, J. Watkins, M. Fenstermacher |
| Description: | In this experiment we try to establish a low density Type III ELMing discharge with good energy confinement by operating near the Type III-Type I power threshold. We also continue a study of the Type III to Type I transition conditions. We will also look for differences in the structure between Type III and Type I ELMs. | ||
| Experimental Approach/Plan: | We will establish a Type III only discharge in with ITER shape operated near the Type III- Type I threshold power to obtain high energy confinement time and examine the Type III characteristics on the UCSD fast camera, magnetics and reciprocating probe to contract to the type I regime. We will then vary q and density to compare the Type III-Type I threshold conditions to previous results and theory. | ||
| Background: | The low density Type III ELM regime is generally though to be an unattractive alternative to the Type I regime for ITER due to the low pedestal pressure gradients obtainable in this regime relative to the Type I regime. However pedestal widths are typically larger in the low density Type III regime compared to the type I regime and previous results have show that much of the confinement is recovered if the discharge is operated near the threshold power for transition between the Type III and Type I regimes. Previous results from DIII-D showed that the power threshold for the Type III/Type I transition scaled as (n/n_GW)**-2, so that operating at low density gave a large margin of power above the H-mode threshold power where the Type III ELM regime could be achieved. In contrast to the Ighitanov/Poguetse theory which predicts a critical betaprime in the pedestal for transition out of the type III regime DIII-D results were more consistent with a critical alpha (q**2*betaprime). No measurements of the Type III ELM energy loss near were made on DIII-D and how Type III ELMs might fit into the filament ejection model for Type I ELMs has never been studied. Type III ELMs need to be reevaluated as an alternative to the Type I regime for ITER. | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | UCSD fast camera, reciprocating probe, langmuir probes, Divertor IR TV. All profile diagnostics | ||
| Analysis Requirements: | Profiles, kinetic EFIT, ELITE stability | ||
| Other Requirements: | Low recycling machine conditions | ||
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