One of the important problems in a tokamak is the existence of inherent thermal instability. For this reason, the control of plasma density and temperature are the most important issues in fusion reactors. We have considered the effect of presence impurity on fusion (50:50) deuterium-tritium plasma parameters in tokamak reactor. This study has been carried out on the base of the particle and energy balance equations in a zero-dimensional model, then the obtained results are compared with the particle and energy balance equations in presence of Beryllium and Argon impurities. We have shown that thermal instability in two states (without impurity and with impurity) then by using refueling rate removed this instability and plasma parameters have thermal stability. The results of our study show that the presence of impurity increases the time to reach steady state and that causes an increase of the plasma temperature, decrease of the plasma density and decrease of β parameter of plasma in a controlled state
