[en] A peak fusion power production of 9.3±0.7 MW has been achieved on the Tokamak Fusion Test Reactor (TFTR) in deuterium plasmas heated by co and counter injected deuterium and tritium neutral beams with a total power of 33.7 MW. The ratio of fusion power output to heating power input is 0.27. At the time of the highest neutron flux the plasma conditions are: T_e(0)=11.5 keV, T_i(0)=44 keV, n_e(0)=8.5x10¹⁹ m^-3, and left-angle Z_eff right-angle=2.2 giving τ_E=0.24 s. These conditions are similar to those found in the highest confinement deuterium plasmas. The measured D-T neutron yield is within 7% of computer code estimates based on profile measurements and within experimental uncertainties. These plasmas have an inferred central fusion alpha fraction of 0.2% and central fusion power density of 2 MW/m³ similar to that expected in a fusion reactor. Even though the alpha velocity exceeds the Alfven velocity throughout the time of high neutron output in most high power plasmas, MHD activity is similar to that in comparable deuterium plasmas and Alfven wave activity is low. The measured loss rate of energetic alpha particles is about 3% of the total as expected from alphas which are born on unconfined orbits. Compared to pure deuterium plasmas with similar externally applied conditions, the stored energy in electrons and ions is about 25% higher indicating improvements in confinement associated with D-T plasmas and consistent with modest electron heating expected from alpha particles. ICRF heating of D-T plasmas using up to 5.5 MW has resulted in 10 keV increases in central ion and 2.5 keV increases in central electron temperatures in relatively good agreement with code predictions. In these cases heating on the magnetic axis at 2Ω_T gave up to 80% of the ICRF energy to ions. copyright 1995 American Institute of Physics