Simulation and Comparative Analysis of Advanced Scenarios for High- and Low-Temperature Superconducting Tokamaks Using METIS Code

The development of steady-state advanced operation modes with high fusion gain (Q) is a primary objective of magnetic confinement fusion research. The advancement of high-temperature superconducting (HTS) magnet technology has introduced a new development path using devices like SPARC. This path contrasts with the conventional low-temperature superconducting (LTS) approach represented by devices such as BEST. This study utilizes the fast integrated modeling code METIS to compare the physical conditions required for HTS-based (SPARC-like) and LTS-based (BEST-like) devices to achieve an energy gain of Q ≈ 5. Furthermore, we simulated the achievable fusion power for both devices under an identical set of core physics parameters to isolate the effect of magnetic field strength. Simulation results show that at a similar Q ≈ 5, the HTS device leverages its high magnetic field to require significantly lower auxiliary heating power (approximately 50–60% less). Additionally, it operates at a lower Greenwald density fraction (f_GW ≈ 0.37) than the LTS device (f_GW ≈ 0.87). This well validates the strong dependence of the fusion triple product on magnetic field strength (∝B³). Under identical high-density (“BEST-like”) parameters, the HTS device achieves much higher fusion power but faces a drastically increased L-H transition power threshold. This increase may force operation in L-mode. Crucially, even in L-mode, there remains the possibility for high-field HTS devices to achieve Q > 5 via high-density operation.