Description
The high poloidal beta (βp) scenario [Ding_Nature2024] is one of reactor-relevant advanced tokamak regimes, combining high confinement (H98y2 > 1.5) with operation at Greenwald fraction ≥ 1. The most specific feature of this scenario is the formation of an internal transport barrier (ITB) at large radius (≥ 0.5), enabled by an optimized current ramp-up phase and current profile shaping that establish favorable magnetic shear conditions to suppress core turbulence.
First demonstrated in JT-60U [Takenaga_NF2005] and subsequently developed in DIII-D, the high βp scenario has been reproduced in several devices as EAST, ASDEX-U, JET and, more recently, also explored in MAST-U, establishing a solid experimental and physics basis. In this invited talk, we focus on how integrated modelling can be used to study the performance and robustness of this scenario, with particular emphasis on access conditions, density evolution toward the Greenwald limit, and the sustainment of the ITB condition during the flat-top phase.
Using an ASTRA–TGLF integrated modelling framework [Bonanomi_NF2025], we study the time-dependent evolution of high βp plasmas in DIII-D, from current ramp-up through flat-top. The analysis highlights the key role of the turbulence stabilization in the formation and sustainment of the ITB, a feature consistently captured by both gyrokinetic studies and the quasi-linear TGLF model. Particular attention is paid to magnetic shear and pressure gradient, and their dominant impact on transport, as well as the effect of the toroidal velocity and its minor role in the formation and sustainment of the ITB.
The validated DIII-D analysis opens the possibility to extend such approach to MAST-U cases to provide insights on the influence of low aspect ratio on current diffusion, turbulence stabilization, and ITB physics.
Finally, the physics understanding gained from present devices is applied to the design of a high βp scenario for the DTT tokamak, currently under construction in Italy. The results illustrate how integrated modelling can guide the development of high-performance, reactor-relevant scenarios in next-step, high-field superconducting machines.