DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 178: Optimal location for fueling pumped DN plasmas | ||
| Name: | Thomas W. Petrie ( |
Affiliation: | General Atomics |
| Research Area: | Boundary | Presentation time: | Not requested | Co-Author(s): | N. Brooks |
| Description: | It is important to determine the most efficient way of fueling DN divertors in order to minimize the amount of deuterium (or tritium) needed to maintain a set density value. With simultaneous pumping on both outer divertor legs of a magnetically balanced high-triangularity DN now possible, DIII-D IS UNIQUELY CONFIGURED TO DETERMINE DEFINITIVELY whether it is more effective to fuel a DN plasma from the high field side or from a divertor versus from the standard low-field side location. Related to this question, it is also important to assess any positive or negative effects to fueling from these locations (e.g., how is tauE affected). This experiment should be done in both forward and reverse toroidal field. | ||
| Experimental Approach/Plan: | A high triangularity, symmetric DN shape is maintained throughout the shot. The upper- and lower outboard cryo-pumps are cold and the inboard (dome) cryo-pump is warm. Conceptually speaking, this approach is made up of four parts: (1) A steady gas puff is injected from the inboard centerpost location into a standard DN H-mode plasma. (2) On the subsequent shot, the same steady gas puff is injected directly into the private flux region of the divertor in the direction of the gradB ion drift. (3) In the third shot, the same steady gas puff is injected from an outboard location (e.g., GasA). We expect that gas injection from the first two locations to yield higher core densities than from GasA. (4) GasA is now programmed to reach the densities achieved in the centerpost puff and divertor puff cases. We expect that more gas will be required to reach these densities using GasA than was used by the gas injectors from the other two locations. It is best to do this experiment in both forward and reverse toroidal field directions in order to account for any effect that differences in the structure of the upper and lower divertors. | ||
| Background: | We have previously found that unpumped DN H-mode plasmas fuel much faster than comparable SN plasmas (PSI1998). In those experiments fueling was done from the outboard vessel side. When gas puffing was used to fuel DNs, an almost immediate detachment of the inboard divertor legs permitted recycled gas from the outboard legs to escape to the inboard side of the core plasma, suggesting after some analysis (UEDGE) that fueling from the inboard side would be more effective than fueling from the outboard side. Experimentally, IR camera and Langmuir probe data from DN cases indicate that both ne and Te may be significantly lower along the inner SOL than along the outboard SOL and that the scrapeoff widths are also narrower on the inboard SOL (PSI2002). We thus expect easier neutrals penetration of the core from the inboard side and thus more effective fueling. An absence of ELMs along the inboard SOL (NF2003) is another reason to expect effective fueling from the inboard side. More recent data from radiating divertor experiments (2007) indicated that injecting impurity (argon) directly into the divertor pointed to by the gradB ion drift direction results in a very rapid impurity ion buildup in the core plasma. Due to the very quick detachment of the inner divertor leg of that divertor, one might expect that deuterium gas injected into the private flux region would also fuel the core plasma just as effectively as from the high field side. | ||
| Resource Requirements: | Machine time: 0.3 (forward Bt) + 0.3 days (reverse-Bt), both upper and lower outer divertor baffle cryo-pumps cold, minimum 5 beam sources. | ||
| Diagnostic Requirements: | Asdex gauges inside both outer baffles, core Thomson scattering, upper divertor and centerpost fixed Langmuir probes, and CER. | ||
| Analysis Requirements: | UEDGE, ONETWO | ||
| Other Requirements: | -- | ||
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