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

Experimental and modeling investigations of high beta (p) scenarios on DIII-D and EAST tokamaks show advantages in high energy confinement, avoidance of n=1 MHD, and core-edge integration with reduced heat flux, making this scenario an attractive option for China Fusion Engineering Test Reactor steady-state operation. Experiments show that plasmas with high confinement and high density can be achieved with neutral beam injection on DIII-D (beta (p) similar to 2.2, beta (N) similar to 3.5, f(BS) similar to 50%, f(Gw) similar to 1.0, and H-98y2 similar to 1.5) and pure RF power on EAST (beta (P) similar to 2.0, beta (N) similar to 1.6, f(BS) similar to 50%, f(Gw) similar to 0.8, and H-98y2 > 1.3). By tailoring the current density profile, a q-profile with local (off-axis) negative shear is achieved, which yields improved confinement and MHD stability. Transport analysis and simulation suggest that the combination of a high density gradient and high Shafranov shift allows turbulence stabilization and higher confinement. Using on-axis Electron Cyclotron Heating injection, tungsten accumulation is avoided on EAST, and this is reproduced in modeling. Reduced heat flux (by > 40%) and maintenance of high core confinement is achieved with active feedback control of the radiated divertor, an important result for long pulse operation in tokamaks. The improved physics understanding and validated modeling tools are used to design a 1GW steady-state scenario for CFETR.

Automated summary

Experimental and modeling investigations of high beta (p) scenarios on DIII-D and EAST tokamaks show that tailored current density profiles can achieve improved confinement and MHD stability by creating q-profiles with local negative shear, leading to turbulence stabilization and higher confinement. The combination of high density gradients and high Shafranov shift allows for improved transport analysis and simulation, resulting in reduced heat flux and maintenance of high core confinement for long pulse operation in tokamaks. These advancements are crucial in designing a 1GW steady-state scenario for CFETR.