DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 369: DiMES Erosion Measurements with Detached Plasmas Induced by Argon Injection | ||
| Name: | Dmitry Rudakov ( |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary | Presentation time: | Not requested | Co-Author(s): | W. Wampler, W. West, T. Petrie, D. Whyte, C. Wong, R. Moyer, S. Allen, N. Brooks, P. Stangeby, J. Boedo, C. Lasnier |
| Description: | DiMES will be used to measure the rate of carbon and tungsten erosion at the outer strike point (OSP) of H-mode plasmas detached by argon injection. This experiment should determine whether argon-detached plasmas can be used with a carbon/tungsten divertor in a tritium fueled next step device. Results will be compared to those from a previous DiMES exposures to plasmas detached by neon injection and semi-detached plasmas with argon injection. | ||
| Experimental Approach/Plan: | This is a continuation of previous DiMES experiments with noble gas injection. A DiMES probe containing depth-marked graphite and tungsten (surface-deposited films or solid buttons) samples will be exposed to the OSP with LSN H-mode plasmas detached by argon injection. Plasma and machine parameters should be close to those used in the previous experiments with neon and argon injection. The OSP should be moved onto the DiMES probe during periods of detached H-mode for a total exposure time of 10-12 seconds (3-4 discharges). Heat flux reduction during Ar injection should be about a factor of 4 compared to the attached phase. Divertor plasma conditions should be characterized to allow comparison of experimental results with erosion/deposition models. Pellet ELM pacing may be used to prevent density runaway in ELM-free H-mode. | ||
| Background: | Carbon and tungsten are the materials currently in the ITER divertor design. A possibility of switching to all-tungsten divertor for D-T phase is being discussed. Divertor detachment is required to reduce heat flux and erosion rates of the targets. With all-tungsten divertor impurity injection will be required to reach the detachment. Previous studies using DiMES showed that net carbon erosion rate at the OSP with neon injection can be rather high even with detachment. Attempts have been made to repeat this experiment with argon injection, but due to various problems the desired plasma conditions were not achieved. During the latest attempt argon injection rate had to be limited because of the density runaway at detachment. As a result, OSP stayed attached through most of the exposure. Preliminary results indicate that tungsten from a surface-deposited strip has eroded. An experiment with better controlled conditions is needed for better extrapolation to ITER. | ||
| Resource Requirements: | 1/2 day experiment; ELMing H-mode, NBI, Ar puff | ||
| Diagnostic Requirements: | DIMES, all available lower divertor diagnostics | ||
| Analysis Requirements: | IBA analysis of the exposed samples | ||
| Other Requirements: | Pellet injection for ELM pacing | ||
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