Carbon dust formation from re-deposited layers in high-density hydrogen/helium plasmas in the NAGDIS-II device

Formation of carbon dust particles on a graphite surface irradiated by a high-density hydrogen plasma and a mixed hydrogen/helium plasma has been investigated in the NAGDIS-II linear divertor plasma simulator. Carbon dust particles are generated at the center region of the graphite surface facing the high-density plasma. No dust particles are formed in the peripheral region. These observations indicate that the re-deposition process of the hydrocarbon ions due to a strong plasma flow at the center of the plasma column is one of the key factors determining the dust growth as well as chemical sputtering.