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It must be removed faster than a certain rate, and it is not certain reactors can do so.","posed_since":"","precise":"Steady burn requires the ratio $\\rho = \\tau_{\\mathrm{He}}*/\\tau_E$ of effective helium particle confinement time to energy confinement time below about 5 to 10. Predict $\\rho$ for ITER and a reactor from core helium transport, edge and divertor helium enrichment and pumping. 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