Fusion yield in He3 plasmas by 10 MW injection of 500 keV deuteron(D)-beam and by up to 30 MW injection of 120 keV D-beam is studied by taking global energy confinement into account. The global energy confinement time, tau E, defined by the ratio of the total stored energy to the input power, is taken to be inversely proportional to the square root of the input power. Higher fusion yield is produced in the regime of lower ne and higher Te, unless the reduction of the He3 density due to the increase of the non-thermal deuteron population is too significant. The hot ion mode of Ti=2Te assumed for high-power 120 keV D-beam injection is found not to be preferable to the Ti=Te mode under the same tau E. The effect of accumulation of thermal deuterons on the fusion yield is also discussed.