Discharge path-dependent bifurcation of plasma confinement on EAST

Abstract We report the first experimental observation of confinement state bifurcation in steady-state H-mode discharges sustained by lower hybrid wave (LHW) current drive and electron cyclotron resonance heating on the EAST superconducting tokamak. The experiments demonstrate that under identical external actuators, plasma confinement evolves into distinct high-performance regimes depending on the initial conditions. Theoretical analysis establishes that this bifurcation mechanism originates from the nonlinear coupling between LHW power deposition dynamics and transport processes: (1) the LHW-driven current profile exhibits strong dependence on real-time plasma parameters (such as the temperature, plasma density and q-profile) and their temporal evolution; (2) transport coefficients display heightened sensitivity to profile gradients during transition phases. Consequently, the plasma reaches different equilibria along various paths. This finding reveals a fundamental interplay between wave-driven current profile control and nonlinear transport dynamics in maintaining steady-state high-confinement plasmas, providing critical insights for ITER and CFETR operation scenarios.