Overview of Alcator C-Mod Research

Alcator C-Mod, a compact (R$=$0.68m, a$=$0.21m), high magnetic field, B$_{\mathrm{t}}\le $8T, tokamak accesses a variety of naturally ELM-suppressed high confinement regimes that feature extreme power density into the divertor, q$_{\mathrm{\vert \vert }}\le $3 GW/m$^{\mathrm{2}}$, with SOL heat flux widths $\lambda_{\mathrm{q\thinspace }}$\textless 0.5mm, exceeding conditions expected in ITER and approaching those foreseen in power plants. The unique parameter range provides much of the physics basis of a high-field, compact tokamak reactor. Research spans the topics of core transport and turbulence, RF heating and current drive, pedestal physics, scrape-off layer, divertor and plasma wall interactions. In the last experimental campaign, Super H-mode was explored and featured the highest pedestal pressures ever recorded, p$_{\mathrm{ped}}\approx $90 kPa (90{\%} of ITER target), consistent with EPED predictions. Optimization of naturally ELM-suppressed EDA H-modes accessed the highest volume averaged pressures ever achieved (\textless p\textgreater \textgreater 2 atm), with p$_{\mathrm{ped}}\approx $60 kPa. The SOL heat flux width has been measured at B$_{\mathrm{pol\thinspace }}=$1.25T, confirming the Eich scaling over a broader poloidal field range than before. Multi-channel transport studies focus on the relationship between momentum transport and heat transport with perturbative experiments and new multi-scale gyrokinetic simulation validation techniques were developed.