AbstractA real-time control function of neutron emission rate has been developed as a first step towards fusion power control. By controlling the number of neutral beam injection units, the neutron emission rate was successfully kept constant for ∼ 5 s until the feedback control was turned off. The plasma stored energy was also kept constant during the same period owing to the correlation between the stored energy and the neutron emission rate. This function is expected to be effective in extending the steady-state performance and in controlling the reactivity of a fusion reactor at Q ≤ 1.