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The purpose of this experiment is to observe and analyze the ablation of carbon-based material samples in the DIII-D SOL and edge plasma environment. Carbon-based materials are widely used as thermal shields protecting spacecrafts during atmospheric entries. For missions involving high-speed atmospheric entries, such as hyperbolic Earth re-entries and probe missions to the gas giants, these shields should withstand extremely high heat fluxes, . Testing and modeling of material performance in this regime is challenging due to the lack of adequate ground testing facilities. As the DIII-D L-mode discharge yields stable plasma and heat fluxes well within the targeted range, this experiment presents a unique opportunity for examining plasma-materials interactions in space-relevant conditions.

The scientific goal of this experiment is to test the predictive capabilities of engineering equations for material mass loss rate in the high heat flux regime. Those equations are initially based on simplified models and available space flight data and will be subsequently refined by comparison with the DIII-D results. The operational goal is to demonstrate that DiMES can be successfully reconfigured to expose material samples in controlled plasma conditions and to provide state of the art diagnostics of the ablation process. The results from this experiment will be used both to benchmark theoretical models and to initiate the performance evaluation of certain carbon-based ablative materials in the high-heat flux regime. This, in turn, will assist the aerospace community in forming the requirements for needed ground testing facilities.

The project objective is to design the carbon rod that can be mounted on the DIII-D DiMES port head. The rod needs to be thermally and electrically isolated. Necessary ANSYS modeling should be done to estimate heat stresses. Several (2-3) rod designs will be done and evaluated. The team will perform the design under the supervision of the UCSD CER researchers (D.M. Orlov and D.L. Rudakov). The team will present the design of the rod to the DIII-D design review committee. The approved design will be manufactured and installed on DIII-D for the experiment scheduled for April of 2021. It is expected that the design of the rod and the results of the DIII-D experiment will be submitted for publication in the Review of Scientific Instruments journal with all the team members included in the list of co-authors.