Prediction and realization of ITER-like pedestal pressure in the high-$B$ tokamak Alcator C-Mod

Fusion power in a burning plasma will scale as the square of the plasma pressure, which is increased in a straightforward way by increasing magnetic field: $P_{fus} \sim p^2 \sim B^4$. Experiments on Alcator C-Mod, a compact high-$B$ tokamak, have tested predictive capability for pedestal pressure, at toroidal field $B_T$ up to $8 \mbox{T}$, and poloidal field $B_P$ up to $1 \mbox{T}$. These reactor-like fields enable C-Mod to approach an ITER predicted value of $90 \mbox{kPa}$. This is expected if, as in the EPED model, the pedestal is constrained by onset of kinetic ballooning modes (KBMs) and peeling-ballooning modes (PMB), yielding a pressure pedestal approximately as $p_{ped} \sim B_T \times B_P$. One successful path to high confinement on C-Mod is the high-density ($\bar{n}_e > 3 \times 10^{20} \mbox{m}^{-3}$) approach, pursued using enhanced D-alpha (EDAs) H-mode. In EDA H-mode, transport regulates both the pedestal profiles and the core impurity content, holding the pedestal stationary, at just below the PBM stability boundary. We have extended this stationary ELM-suppressed regime to the highest magnetic fields achievable on C-Mod, and used it to approach the maximum pedestal predicted by EPED at high density: $p_{ped} \approx 60 \mbox{kPa}$. Another approach to high pressure utilizes a pedestal limited by PBMs at low collisionality, where pressure increases with density and EPED predicts access to a higher ``Super H'' solution for $p_{ped}$. Experiments at reduced density ($\bar{n}_e < 2 \times 10^{20} \mbox{m}^{-3}$) and strong plasma shaping ($\delta > 0.5$) accessed these regimes on C-Mod, producing pedestals with world record $p_{ped} \approx 80 \mbox{kPa}$, at $T_{ped} \approx 2 \mbox{keV}$. In both the high and low density approaches, the impact of the pedestal on core performance is substantial. Our exploration of high pedestal regimes yielded a volume-averaged pressure $\langle p \rangle > 2 \mbox{atm}$, a world record value for a magnetic fusion device. The results hold promise for the projection of pedestal pressure and overall performance of high field burning plasma devices.