[en] The first experiment simulating helium ash exhaust in a DT fusion reactor has been performed in the JT-60 tokamak with L-mode divertor discharges. He was injected with a 30-keV neutral beam to realize core fueling. Divertor neutral pressures of hydrogen and He increased in proportion to the cube of the electron density of the main plasma. The He enrichment factor was 0.5 at bar n_e=6x10¹⁹ m^-3 and increased in proportion to n_e. In an L-mode plasma of a fusion reactor, thermalized α particles (He ash) generated in the core plasma can be easily exhausted with a pumping speed of several tens m³/s