Stability analysis of magnetohydrodynamic instabilities for H-mode scenario in CFEDR

Global magnetohydrodynamic (MHD) instabilities are assessed for a reference H-mode scenario designed for the China Fusion Engineering Demo Reactor (CFEDR) with a normalized beta of \beta _\mathrmN=2.6 and a safety factor of q_95=5.3 . For this scenario, the Troyon no-wall beta limit and ideal-wall beta limit computed by MARS-F code are \beta _\mathrmN^\mathrmN\mathrmW=2.8 and \beta _\mathrmN^\mathrmI\mathrmW=3.1 , respectively. This means that it is stable against the external kink mode for the target plasma pressure. However, even with a stable classical tearing mode (TM) via optimization of the q-profile, the 2/1 neoclassical tearing mode (NTM) remains significantly unstable and can be triggered if the seed island exceeds 5 cm in width. Therefore, electron cyclotron current drive can be employed to stabilize this mode, with the necessary driven current amounting to 1% of the plasma current. Additionally, in both the plasma ramp-up and high-confinement flat-top stages, the error field tolerance of CFEDR ( b_\mathrmr/B_\mathrmT\sim 5.7\times 10⁻⁵ and b_\mathrmr/B_\mathrmT\sim14.6\times 10⁻⁵) is larger than that of ITER ( b_\mathrmr/B_\mathrmT\sim2.7\times 10⁻⁵ and b_\mathrmr/B_\mathrmT\sim11\times 10⁻⁵), respectively, in Ohmic cases. The positional accuracy of the poloidal field coils and center solenoid coil should be controlled within 3.5 mm for shifts in order to reduce the intrinsic error field to within the specified tolerance. This reference H-mode scenario is being designed to operate in high-q₉₅ and high-plasma pressure, which will reduce the error field tolerance due to the resonant field amplification effect and NTM locking, as well as the actual beta limit. Therefore, further assessments for dynamic error field correction with higher plasma pressure are required.