Predicting pedestal pressure height and width in reactor conditions
In plain words
The pressure reached at the top of the edge layer largely decides how much fusion power a tokamak makes. Models that predict it work in many present machines but fail in some, such as those with metal walls and heavy gas fueling.
Precise statement
Pedestal models of the EPED type combine the ideal peeling-ballooning stability limit with a kinetic-ballooning-mode constraint on pedestal width (width ~ beta_pol,ped^0.5) to predict the pedestal pressure $p_{\mathrm{ped}}$. Determine what additional physics (separatrix density and neutral fueling, microtearing or electron-temperature-gradient transport, resistive and diamagnetic effects) is needed to predict $p_{\mathrm{ped}}$ to within 20 percent at high separatrix density, high gas fueling and metal walls, and give the prediction for ITER $Q = 10$. An answer is a model validated on at least three devices including a metal-wall one.
What would settle it
Blind pedestal predictions agreeing with measured $p_{\mathrm{ped}}$ within 20 percent on multiple devices, including high-fueling metal-wall discharges, followed by ITER H-mode data.
Status in the literature
Unverified note
EPED-type models reproduce pedestal heights in many conventional H-modes but miss the degradation seen at high fueling and separatrix density, as in metal-wall JET; no accepted extension was known as of mid-2026.