In this paper, ignition curve for deuterium/helium-3 fusion reaction is studied. Four fusion reactions are considered. Zero-dimensional model for the power balance equation has been used. The closed ignition curves for ρ = constant (ratio of particle to energy confinement time) have been derived. The results of our calculations show that ignited equilibria for deuterium/helium- 3 fuel in a spherical tokamak is only possible for ρ = 5.5 and 6. Then, by using the energy confinement scaling and parameters of the spherical tokamak reactor, the plasma stability limits have been obtained in ne, T plane and, to determine the thermal instability of plasma, the timedependent transport equations have been solved.
