The optimal values of Greenwald density limit and plasma safety factor in inductive and non-inductive operation modes

The spherical tokamak (ST) operates in a steady state with a high fusion gain. The 0-dimensional power balance model, including radiation losses to determine Q value as an inductive fusion gain, and the current balance model for determining \(Q_{\textrm{CD}}\) as a non-inductive fusion gain, is used to investigate the viability of D–\(^{3}\)He fuel for a steady-state operation. The spherical tokamak’s geometry, including the magnetic field \(B_{t}\) and \(\beta _{\textrm{th}}\) as a ratio of its kinetic pressure to the magnetic pressure, is used to analyse the impact of the confinement enhancement factor \(H_{y2}\) and the impurity density fraction \(f_{\textrm{I}}\) on \(Q_{\textrm{CD}}\). By comparing the obtained values with the device data, plasma characteristics, such as the safety factor \(q_{\textrm{I}}\) and Greenwald density limit \(N_{\textrm{G}}\) are examined to determine the optimum density limit and safety factor for an assurance about \(Q\approx Q_{\textrm{CD}}\) as the aim of steady-state operation. A comparison with ARIES-III performance is also made. The overall plant power balance equation is included. Furthermore, the desirable plant thermal efficiency value \(\eta _{\textrm{th}}\) and normalised beta value \(\beta _{N}\) for producing net electric power \(P_{\textrm{NET}}>\) 1 GW for the ST are achieved. Therefore, ST’s capability of having a lower aspect ratio A and higher elongation \(\kappa _{s}\) than ARIES-III in generating more significant fusion power with lower \(H_{y2}\) and higher energy confinement time \(\tau _{E}\) is approved.