Formation of hot spots and arc ignition on tungsten with nano-tendril bundles under high-density hydrogen plasma exposure.

Nano-tendril bundles (NTBs) are clusters of fuzzy nanostructures that form on tungsten surfaces when they are exposed to helium plasmas under specific conditions, reaching lengths of over 100 µm. Tungsten samples with NTBs and fuzz were exposed to high-density hydrogen plasmas in the Upgraded Pilot-PSI linear plasma device to investigate their response, with a particular focus on unipolar arc ignition and hot spot formation. Although NTBs are prone to arcing due to their high field electron emission characteristics, unipolar arcs have never occurred on NTBs. Post-mortem analysis showed that the heights of the NTBs changed significantly during irradiation mainly due to rapid heating, and that these changes strongly influenced their interaction with high-density plasmas.