DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 407: ITER Mirror performance test. Active control over the deposition on the mirrors by the gas feed. | ||
| Name: | Andrey Litnovsky ( |
Affiliation: | Forschungszentrum Juelich |
| Research Area: | Boundary | Presentation time: | Not requested | Co-Author(s): | D. Rudakov (UCSD), V. Philipps (FZJ), C. Wong (GA), W. West (GA), R. Boivin(GA), N. Brooks (GA), P. Wienhold (FZJ), G. Sergienko (FZJ), R. Bastasz (SNL), J. Whaley (SNL), W. Wampler (SNL), J. Watkins (SNL), J. Brooks (ANL), T. Evans (GA), D. Whyte (UW), P. Stangeby (Univ. of Toronto), A.Mclean (Univ. of Toronto), J. Boedo (UCSD), R. Moyer (UCSD) |
| Description: | This experiment is the further continuation of the tests of ITER candidate mirror materials under ITER relevant plasma conditions. The goal is to study the efficiency of the gas feed in front of the mirror to mitigate the deposition on the mirror surface | ||
| Experimental Approach/Plan: | Following the results obtained in 2005 and 2006 when the dedicated experiments were done with diagnostic mirrors in the divertor of DIII-D, the continuation of this program is proposed. In the experiments made in 2005 and 2006, the suppression of carbon deposition was demonstrated in the experiment made in 2005 and the complete preservation of mirror optical characteristics was achieved in the experiment made in 2006. The gas feed in the vicinity of mirror is another attractive option to mitigate the impurity deposition and degradation of the optical properties of the diagnostic mirrors which should be tested in divertor environment.
It is planned to expose the set of mirrors in the private flux region for series of identical ELMy H-Mode discharges similar to those used in 2005-2006 experiments. The exposure is to be made using the DiMES Mirror holder. Molybdenum mirrors will be used for the experiment. The gas flow of D in the vicinity of mirrors will be realized using the existing gas feed system located near the DiMES transport system. Total exposure time of >40 seconds (>8 plasma discharges) is requested. | ||
| Background: | Metallic first mirrors are currently foreseen for all optical and laser diagnostics of ITER. The mirrors will be subject to erosion, deposition and particle implantation which will degrade their properties and impact the performance of entire respective diagnostic systems in ITER. The robust solution is needed to ensure the optimal performance of diagnostic mirrors in ITER throughout the whole lifetime of the machine. The development of the deposition mitigation techniques is of crucial importance to make such a solution possible.
The investigations on first mirrors are presently recognized as High Priority Task of the ITPA Topical Group on Diagnostics and are the subject of IEA-ITPA Joint Experiments Program (Task DIAG 2). The importance of the R&D program on first mirrors was outlined in the recent ITER Diagnostics review, carried out in Cadarache, France in July 2007. The first-ever dedicated experiment with ITER-candidate mirror materials under ITER-relevant conditions was performed in DIII-D divertor in April 2005. This experiment confirmed that mirrors in detached divertor suffer from carbon deposition. It also delivered important information on the active deposition mitigation on divertor mirrors by elevated temperature. The subsequent experiment in 2006 has demonstrated the capability to prevent the carbon deposition and degradation of optical properties by heating the mirrors. Another promising technique presently being assessed for several ITER diagnostics, is the gas feed in front of the mirrors protecting them from deposition of impurities. In the pilot experiment performed in TEXTOR it was demonstrated that the gas feed is capable to prevent the carbon deposition on the mirrors directly exposed in plasma. We need to elaborate this technique further and to prove that the gas feed is efficient enough to gain the control under deposition in the ITER-relevant divertor conditions. | ||
| Resource Requirements: | Machine Time: 1/2 day experiment
Number of neutral beam sources: 3 | ||
| Diagnostic Requirements: | all SOL and lower divertor diagnostics, DiMES TV, core Thomson scattering, CER. | ||
| Analysis Requirements: | SIMS, XPS, Ellipsometry, Reflectivity measurements, NRA, DEKTAK profiling (the most of analyses will be provided by FZJ) | ||
| Other Requirements: | Plasma shape and discharge parameters similar to those of experiment with molybdenum mirrors performed on September 8, 2006 | ||
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