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Mapping of blobs/filaments from miplane to divertor target

Proposed by J.L. Terry, B. LaBombard , I. Cziegler , S. Zweben , and O. Grulke. How do SOL filaments map onto divertor targets? Are filaments sheared apart as they pass near the X-pt (Cohen,Ryutov 1 )?

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Mapping of blobs/filaments from miplane to divertor target

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  1. Proposed by J.L. Terry, B. LaBombard, I. Cziegler, S. Zweben, and O. Grulke • How do SOL filaments map onto divertor targets? • Are filaments sheared apart as they pass near the X-pt (Cohen,Ryutov1)? • Does the current carried by the filament perturb the field locally so as to move the filament out radially at the target (Krashenninikov2)? Mapping of blobs/filaments from miplane to divertor target Background: Motivation: • Maqueda, et al.3 show NSTX filaments reaching the targets for rfil>rcrit. • Existing C-Mod data show strong cross-correlation between miplane GPI and target probes (F-port floor), as well as between GPI and FSP. • However, this occurs with a EFIT mapping that that deviates from actual geometry (Dr~7 mm & Dz ~ 6 cm) 1 Cohen & Ryutov NF 37 (1997) p 621. 2 private communication 3Maqueda, et al., NF 50 (2010) p 75002. C-Mod Ideas Forum: Jan. 10-12, 2011

  2. Mapping of blobs/filaments from miplane to divertor target These are low q (q95=3.1)configurations However, these peak correlations/mappings are for mappings that differ from those predicted by EFIT, i.e. Bt=0.925 BtEFIT and midpl view of max corr. maps to an R< the actual R of the probe! C-Mod Ideas Forum: Jan. 10-12, 2011

  3. To date we have only successfully mapped probes above the nose to the 2D GPI view, thus run shots which map those F divertor probes that are closer to the strike pt into the GPI view. Observe at what r’s correlation is observed. • The mapping occurs at q95~3.1. Previous observation was at Bt=3.62T. Scan Bt and Ip, keeping q fixed to see if observed mismatch in r scales with Bp, as it should if the filaments currents are perturbing the local field. • Measure the distribution of time lags • for maximum correlation to see if the • filaments propagate from midplane to • divertor or are born along outboard flux • tubes at the same time (i.e. k||=0). Mapping of blobs/filaments from miplane to divertor target Plan: preliminary: ~3ms lag between GPI & FSP 1 dedicated run is needed. C-Mod Ideas Forum: Jan. 10-12, 2011

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