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Effects of metal impurity re-cycling in the scrape-off plasma of a large tokamak

Re-cycling of self-sputtered impurities from a limiter or a divertor neutralizer plate is investigated numerically. An upper limit for the boundary plasma temperature is determined from the condition that wall material impurity ions do not increase. This temperature is shown to be very low in a conventional tokamak but not limited in a divertor tokamak with a molybdenum neutralizer plate.