First impurity powder injection experiments in LHD

Nespoli, F ; Ashikawa, N.; Gilson, E. P. ; Lunsford, R. ; Masuzaki, S.; Shoji, M.; Oishi, T.; Suzuki, C.; Nagy, A. ; Mollén, A. ; Pablant, N. A. ; Ida, K.; Yoshinuma, M.; Tamura, N.; Gates, D. A. ; Morisaki, T.; experiment group, LHD
Issue date: 2020
Creative Commons Attribution 4.0 International (CC BY)
Cite as:
Nespoli, F, Ashikawa, N., Gilson, E. P., Lunsford, R., Masuzaki, S., Shoji, M., Oishi, T., Suzuki, C., Nagy, A., Mollén, A., Pablant, N. A., Ida, K., Yoshinuma, M., Tamura, N., Gates, D. A., Morisaki, T., & experiment group, LHD. (2020). First impurity powder injection experiments in LHD [Data set]. Princeton Plasma Physics Laboratory, Princeton University.
  author      = {Nespoli, F and
                Ashikawa, N. and
                Gilson, E. P. and
                Lunsford, R. and
                Masuzaki, S. and
                Shoji, M. and
                Oishi, T. and
                Suzuki, C. and
                Nagy, A. and
                Mollén, A. and
                Pablant, N. A. and
                Ida, K. and
                Yoshinuma, M. and
                Tamura, N. and
                Gates, D. A. and
                Morisaki, T. and
                experiment group, LHD},
  title       = {{First impurity powder injection experime
                nts in LHD}},
  publisher   = {{Princeton Plasma Physics Laboratory, Pri
                nceton University}},
  year        = 2020,
  url         = {}

Injection of impurities in the form of sub-millimeter powder grains is performed for the first time in the Large Helical Device (LHD) plasma, employing the Impurity Powder Dropper (IPD) [A. Nagy et al., RSI 2018], developed and built by PPPL. Controlled amounts of boron (B) and boron nitride (BN) powder are injected into the helical plasma. Visible camera imaging, UV and charge exchange spectroscopy measurements show that the injected impurities effectively penetrate into the plasma in two different magnetic configurations.The prompt effects of the impurities on the plasma are characterized as the injection rate is scanned. The injected impurities provide a supplemental electron source, causing the plasma density to increase, together with the radiated power. Beneficial effects on the confined plasma temperature are observed at low plasma densities, due to an increased efficiency in NBI power absorption. For $n_{e,av}<10^{19}m^{-3}$ the powder grains penetrate deeper into the plasma, as they can be less effectively deflected by the plasma flow in the divertor leg, which they have to cross first as they are injected from the top of the machine.In this case, the created B ions are observed to move outwards from UV spectroscopy and charge exchange measurements, due to the outwards direction of the radial electric field. This makes low density plasmas a better candidate for powder boronization techniques.

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