Determining the access to H–mode in the ITER pre–fusion and fusion power operation phases at low plasma current with full–radius TGLF–SAT2 simulations of L–mode plasmas

Abstract

The pre–fusion power operation 1 phase of ITER is planned to be characterized by electron cyclotron resonance heating only. Under the assumption that the access to H–mode is determined by a critical ion heat flux at the plasma edge, full–radius ASTRA simulations with the TGLF–SAT2 transport model are performed in order to compute the ion heat flux produced by the thermal exchange between electrons and ions in different operational conditions. Both hydrogen and deuterium plasmas at 5MA are considered, respectively at 1.8T and 2.65T, corresponding to one third and half of the nominal maximum magnetic field. Different levels of electron cyclotron heating power are considered in sets of simulations with increasing values of the electron line averaged density. The predictions are compared with the currently available scaling of the critical ion heat flux. In hydrogen, 20MWof electron heating power are predicted
to allow H–mode access in a vanishingly small density window, whereas 30MW and 40MW would allow more substantial H–mode operational windows. Despite the fact that in deuterium plasmas the thermal exchange between electrons and ions is smaller
by the hydrogen to deuterium mass ratio compared to hydrogen plasmas, the lower H–mode power threshold in deuterium leads to the prediction that an even broader and more robust domain to access H–mode is obtained at half field at 40 MW in deuterium as compared to operation in hydrogen at one third of the maximum magnetic field, even at the same power.

Full-radius integrated modelling of ASDEX Upgrade L-modes including impurity transport and radiation

“…As boundary condition we use the 2-point model for T e,sep [36], with a heat flux width λ q from the heuristic drift model [37], and we set T i,sep = 1.5 T e,sep , n e,sep = 0.3⟨n e ⟩ vol like in [14]. The radial electric field E r becomes particularly relevant at the edge of ion heated discharges at powers approaching the L-H transition, through its role on the E×B shearing [38]. Our description is based on the work of [39], where the edge E r well is mimicked by solving the ion force balance until a radial position ρ min in the normalized poloidal flux ρ pol , then forcing E r to zero at the separatrix (thus E r has a local minimum at ρ min ), such that…”