Re-Deposition Dynamics of Trace 13C in H-mode Divertor Conditions

This contribution focuses on a particular local impurity transport mechanism, "walking" [1], based on re-erosion of C, which is believed to have a significant capability to accumulate impurities into remote divertor corners, possibly forming thick hydrogen-rich deposits. To this end, we revisit the JET 2004 and 2009 tracer injection experiments, in which the experimental campaigns were concluded by injecting 13CH4 into series of identical ELMy H-mode plasmas in the scrape-off layer at the outer divertor. The first experiment is described in detail in [1], where a consistent picture of 13C migration in a global scale was achieved by extensive modelling with the EDGE2D/NIMBUS code suite. However, local modelling of this experiment [2] has not yet successfully matched divertor plasma conditions, impurity emission and post-mortem measurements simultaneously. The 2009 experiment and corresponding local modelling has been reported in [3], but the modelling has been extended to employ a long-range migration model that will be described in detail in a subsequent paper. First results shown in this paper illustrate that the deposition on the entire divertor can be much better explained with the extended model. Although the present contribution still focuses on JET results with the carbon wall, walking is a result of sputtering and therefore relevant for all impurity species. Moreover, co-deposition of hydrogen is relevant for beryllium as well. Available tracer injection data is still dominated by 13C as the opportunities to gather data only occur once a campaign.
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