EMC3-EIRENE modeling of boron transport in DIII-D L-mode real-time wall conditioning experiments

<p>Observations from powder injection experiments in ASDEX-U and DIII-D showed improvements in the wall conditions in response to boron (B) or boron nitride (BN) injection in H-mode plasmas [1, 2]. Recent experiments have been performed in DIII-D to understand the physics of boron impurity transport during real-time wall conditioning via B powder injection. For this purpose, B powder was injected gravitationally in DIII-D at rates between 2-50 mg/s in 4 s flat top L-mode scenarios with the magnetic field in the unfavorable &nabla;B drift direction. Graphite and W-coated witness samples were introduced using the divertor material evaluation system (DiMES) for in-depth analysis of the deposited impurity layers.<br> Observations with a spectroscopically filtered camera showed evidence of striation patterns in the CII and BII emission on the divertor floor extending in the toroidal direction. Post-mortem analysis of the DiMES samples showed corresponding striation patterns alternating between strongly-coated and barely-coated regions. Secondary peaks in the divertor density and temperature obtained with Langmuir probes support the interpretation of a significant static magnetic perturbation affecting the scrape-off layer (SOL) background plasma and impurity transport during these experiments.<br> These effects visible in the SOL transport and plasma-surface interactions are investigated based on an analysis of potential error field effects and local source effects. First, the magnetic boundary and divertor footprints are analyzed based on equilibrium reconstruction, including static magnetic perturbations to account for known error fields. Then, the fully 3D plasma-fluid and kinetic edge neutral transport Monte-Carlo code EMC3-EIRENE is employed to resolve the effects of these error fields on SOL impurity transport and impurity fluxes onto the divertor. The structure and widths of the deposition patterns will be studied as a function of anomalous cross-field transport and impurity source location and compared with the experimental findings. This work will contribute to optimizing improvements in the wall conditions in response to B and BN powder injection recently observed on many confinement devices around the world [3, 4].</p> <p>[1] A. Bortolon et al., Nucl. Mater. and Energy, 384-389 (2019) 19</p> <p>[2] R. Lunsford et al., Nucl. Fusion 126034 (2019) 59</p> <p>[3] A. Nagy et al Rev. Sci. Instrum., 10K121 (2018) 89</p> <p>[4] R. Maingi et al., Nucl. Fusion, 024003 (2018) 58</p>