DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 361: Scaling of H-mode pedestal width with rhostar | ||
| Name: | Tom Osborne ( |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics | Presentation time: | Not requested | Co-Author(s): | L. Horton (AUG), M. Beurskens(JET), A. Leonard, R. Groebner |
| Description: | The scaling of H-mode pedestal width with rhostar is determined by comparing otherwise dimensionally similar discharged on DIII-D/JET/Asdex-Upgrade. This would verify the results obtained on DIII-D which showed no rhostar dependence over a variation of about 50% in rhostar to a factor of 4 in rhostar by comparison with JET high field discharges and verify the result by comparison with Asdex-Upgrade. | ||
| Experimental Approach/Plan: | The recent completion of the JET high resolution thomson scattering system (HRTS) now allows the scaling of the pedestal width with rhostar to be determined over a wide range in rhostar by comparison of DIII-D/AUG with small size at low field (large rhostar) to JET with large size and high toroidal field (small rhostar). For each machine discharges would first be made with all dimensionless parameters matched in the H-mode pedestal region, then AUG and DIII-D would push to low Bt increasing rhostar while keeping the other dimensionless parameters fixed while JET would push to high field and small rhostar. It is though a range of a factor of 4 in rhostar should be obtainable. | ||
| Background: | Simple theoretical arguments suggests that the H-mode pedestal width should decrese with decreasing rhostar. Even a small dependence on rhostar would reduce the preformance of a large, small rhostar, machine like ITER by reducing the obtainable pedestal pressure within the edge stability constraing. The importance of determining this scaling for ITER lead to it being listed as ITPA experiment PEP-2. The previous JET/DIII-D pedestal comparison experiment gave similar normalized pedestal widths when all dimensionless parameters were matched and showe no dependence of the width on rhostar in a scan of about 50% on DIII-D alone. In these experiments good profile data could not be obtained from JET at high field and the experiment could not be completed as planned. JET's new high resolution Thomson system will low allow each machine to independently do a rhostar variation while overlapping at the dimensionally matched point to give a wide rhostar range and finally complete PEP-2. Previous results also showed an increase in ELM size with increasing rhostar that could be helpful for ITER. | ||
| Resource Requirements: | Discharge shapes will be matched between JET, DIII-D and AUG possibly requiring some discharge development. | ||
| Diagnostic Requirements: | Profile diagnostics are essential. ELM diagnostics. | ||
| Analysis Requirements: | Profiles including rotation, kinetic EFIT, ELITE. | ||
| Other Requirements: | AUG and JET participants would travel to GA to take part requiring careful scheduling | ||
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