DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 281: Production of a Mass gradient in DIII-D Discharges | ||
| Name: | Jim Leuer ( |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges | Presentation time: | Not requested | Co-Author(s): | J. Leuer, A. Hyatt, M. Schaffer, T. Jernigan |
| Description: | In DIII-D most discharges use D as the primary gas; occasionally H or He is used. However, considerable differences in plasma transport and MHD (ie ELM'S) are observed using different gas species. We propose establishing a mass species gradient in DIII-D using H gas puffing or recycling at the edge and D beam and/or pellet injection in the core to establish the largest gradient permissible in the device. If we can achieve a large gradient in mass we would expect standard core D plasmas with favorable edge H parameters. This has direct bearing on ITER with the ability to vary the reactivity, MHD characteristics near the edge. This could add another tool for the control internal plasma profiles. | ||
| Experimental Approach/Plan: | This experiment will try to establish a mass gradient over the plasma radius. We will use beam/pellet and gas_puff/recycling to control the core and edge, fuel sources, respectively. Nominally we will use D for the core and H for the edge. We want to balance the core/edge fueling to maximize the the gradient while maintaining the plasma below global density limits. Initial testing will be with L-mode plasma since it is expected we can achieve the best control over the sources and thus establish the largest gradients. We would run 4 discharges types, identical except for fueling sources: 1) All D 2) All H, 3) D-core, H-edge, 4) H-core, D-edge. Diagnostics techniques to measure the gradients are expected to be difficult. However, using four different types above should enable us to compare global parameters and infer the impact on transport and MHD the mass variation provides. We might even try (H and He) to maximize the mass ratio effect. If successful we would extend the studies to H-mode plasmas and infer any benefits to ITER type discharges. | ||
| Background: | Most all tokamaks explore uniform mass (all D or all H) over the cross section of the device. The primary assumption is that a final single 50/50 mixture of D/T is ideal for a fusion power plant. However, toward the edge of a ignited plasma the low temperature would greatly reduce the importance of the edge to overall energy balance. A 50% DT mixture is not needed. However, edge region is critical to the success of reactors and a number of phenomena could be modified by different isotopes in the edge. In a device like ITER it could run with a larger fraction of deuterium in the plasma edge to reduce the tritium uptake in the wall. Transport is expected to be much different in a deuterium edge and will impact interactions in the divertor. Alternatively, we may increase the edge mass number by introducing only T at the edge while fueling a 50/50 mixture in the core. We need to explore how far edge species migrate up stream and what impact a lighter (or heavier) mass will have on the edge behavior. Ultimately, this gives us another knob to control profiles in the tokamak and an area that has not been explored to date. | ||
| Resource Requirements: | NBI sources especially tangential, upper and lower cryopumps, inner pellet injectors | ||
| Diagnostic Requirements: | Full set of diagnostics - with emphasis on spectroscopic analysis to determine H/D/(He) Isotope gradients. | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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