DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 179: Effect of particle drifts on particle exhaust in an ITER-like configuration | ||
| Name: | Thomas W. Petrie ( |
Affiliation: | General Atomics |
| Research Area: | Boundary | Presentation time: | Not requested | Co-Author(s): | N. Brooks |
| Description: | ITER has chosen the pumping of neutrals from the private flux region as its method of particle control. To-date, modeling of the effectiveness of this approach has been done but this modeling presently does not include the effect of particle drifts in the divertor, such as those involving ExB, might have on these results. It is the intention of this experiment to evaluate whether or not neglecting these drifts can an appreciable effect on particle exhaust and detachment, when particle control is based on pumping on the private flux region. Note that detachment is crucial to ITER in maintaining power loading to acceptable values and we know that it also would be affected divertor particle drifts. Hence, these are rather important issues that need to be resolved sooner rather than later. | ||
| Experimental Approach/Plan: | An upper SN plasma (dRsep > +3 cm) has its outer strike point on the side of the outer baffle just above the entrance to the outer baffle. Simulate the ITER plasma shape as much as practical. The inner strike point is tangent to the dome next to the entrance to the inner pump plenum. Only the upper outer pump is at liquid helium temperature. Hence, neither the inner nor the outer strike points are pumped directly; only neutrals from the private flux region are pumped. This configuration is similar to the pumping setup describe in the ITER Technical Basis [G A0 FDR 1 01-07-13 R1.0], except for absence of a semi-permeable dome located between the pump and the private flux region.
The experiment is straightforward. The main parameter scan is core density and pumping rate vs gas puff rate (from the bottom of the vessel). The range in core density for which the plasmas are attached and detached and the neutral pressure values in the private flux region and inside the upper outer plenum are determined in both forward and reverse Bt cases. | ||
| Background: | The geometry of the ITER divertor has been based on simulations obtained using the B2-EIRENE Monte Carlo code and by extrapolation from results of tokamak experiments. The reference configuration for the ITER divertor is a vertical target/baffle with an open private flux region and a dome below the Xpoint. Neutrals that have entered the dome (which is partially open to neutrals from the inner and outer divertor legs) can then be pumped out of the vessel. Also, the magnetic field lines intercept the vertical target at an acute angle for power spreading on a larger wetted area and for easier partial detachment.
The calculations used to evaluate pumping expectations were based on models that do not include the particle drifts that studies at DIII-D have indicated play a very large roles in particle behavior in the divertor. We can simulate the ITER pumping scenario well enough to determine whether or not neglecting drifts are important for ITER. In addition to experimental verification, the progress that UEDGE has made in modeling these types of plasmas with drifts, particularly the Etheta x B and the Er x B drifts, should provide a theoretical underpinning to our measurements. Etheta is the poloidal component of the electric field on an SOL flux surface, arises principally from the poloidal gradient in Te on that flux surface, and is directed toward the divertor target. | ||
| Resource Requirements: | Machine time: 0.25 (forward Bt) + 0.25 days (reverse-Bt), upper outer divertor baffle cryo-pump is at liquid helium temperature, minimum 6 beam sources. | ||
| Diagnostic Requirements: | Asdex gauges inside both outer baffles, core Thomson scattering, upper divertor and centerpost fixed Langmuir probes, upper divertor IRTV, and CER. | ||
| Analysis Requirements: | UEDGE, ONETWO | ||
| Other Requirements: | -- | ||
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