Advanced tokamak investigations in full-tungsten ASDEX Upgrade

The appropriate tailoring of the q-profile is the key to accessing Advanced Tokamak (AT) scenarios, which are of great benefit to future all-metal fusion power plants. Such scenarios depend on low collisionality ν* which permits efficient external current drive and high amounts of intrinsic bootstrap current. At constant pressure, lowering of the electron density n_e leads to a strong decrease in the collisionality with increasing electron temperature ν* $∼Te−3$⁠. Simultaneously, the conditions for low n_e also benefit impurity accumulation. This paper reports on how radiative collapses due to central W accumulation were overcome by improved understanding of the changes to recycling and pumping, substantially expanded ECRH capacities for both heating and current drive, and a new solid W divertor capable of withstanding the power loads at low n_e. Furthermore, it reports on various improvements to the reliability of the q-profile reconstruction. A candidate steady state scenario for ITER/DEMO (q₉₅ = 5.3, β_N = 2.7, f_bs > 40%) is presented. The ion temperature profiles are steeper than predicted by TGLF, but nonlinear electromagnetic gyro-kinetic analyses with GENE including fast particle effects matched the experimental heat fluxes. A fully non-inductive scenario at higher q₉₅ = 7.1 for current drive model validation is also discussed. The results show that non-inductive operation is principally compatible with full-metal machines.