Advances in physics understanding of high poloidal beta regime towards steady-state operation of CFETR

Experimental and modeling investigations on EAST and DIII-D show how plasma current profiles, turbulent transport and radiation properties self-consistently evolve toward fusion relevant steady state conditions. Integrated experiments on EAST demonstrate that high $\beta _{\mathrm{P\thinspace }}$(\textasciitilde 2.0), fully non-inductive, moderate bootstrap current fraction (f$_{\mathrm{bs}}$50{\%}) plasmas are maintained over 40 current relaxation times with metal wall, low rotation and small ELMs at high density (n$_{\mathrm{e}}$/n$_{\mathrm{GW}}$\textasciitilde 0.80) and using only RF H{\&}CD. The current density profile was broadened at higher density and higher $\beta_{\mathrm{P}}$ operation, with an increase of f$_{\mathrm{bs}}$, leading to a slightly reversed shear profile, which contributes to the increase in energy confinement, similar to observations on DIII-D. The improved confinement was observed at high $\beta _{\mathrm{P}}$, consistent with lower electron turbulence measurement. The achieved small ELMs facilitate RF power coupling in H-mode phase and reduce divertor sputtering/erosion. Low tungsten concentration was observed at high $\beta_{\mathrm{P\thinspace }}$with a hollow profile in the core region. Reduction of the peak heat flux on the divertor with f$_{\mathrm{rad}}$ up to 40{\%} was compatible with high $\beta_{\mathrm{P}}$ scenario by using active radiation feedback control. Modeling and physics experiments confirmed synergistic effects between ECH and LHW, where ECH enhances heating and current drive from LHW injection, enabling fully non-inductive operation at higher density. On DIII-D, high normalized fusion performance results from a large radius ($\rho $\textasciitilde 0.7) internal transport barrier, observed at high $\beta_{\mathrm{P}}$ (\textgreater 2.0) and high normalized density (n$_{\mathrm{e}}$/n$_{\mathrm{GW}}$\textasciitilde 1.0), and consistent with the effect of Shafranov shift stabilization of turbulence. Excellent confinement in this regime is insensitive to plasma rotation. These results increase confidence in the extrapolation of the high $\beta_{\mathrm{P}}$ regime to steady state scenarios for CFETR.