Boundary plasma heat flux width measurements for poloidal magnetic fields above 1 Tesla in the Alcator C-Mod tokamak

The boundary heat flux width, along with the total power flowing into the boundary, sets the power exhaust challenge for tokamaks. A multi-machine boundary heat flux width database found that the heat flux width in H-modes scaled inversely with poloidal magnetic field ($B_{\mathrm{p}})$ and was independent of machine size. The maximum $B_{\mathrm{p}}$ in the database was \textasciitilde 0.8 T, whereas the ITER 15 MA, Q$=$10 scenario will be 1.2 T. New measurements of the boundary heat flux width in Alcator C-Mod extend the international database to plasmas with $B_{\mathrm{p}}$ up to \textasciitilde 1.3 T. C-Mod was the only experiment able to operate at ITER-level $B_{\mathrm{p}}$. These new measurements are from over 300 plasma shots in L-, I-, and EDA H-modes spanning essentially the whole operating space in C-Mod. We find that the inverse-$B_{\mathrm{p}}$ dependence of the heat flux width in H-modes continues to ITER-level $B_{\mathrm{p}}$, further reinforcing the empirical projection of \textasciitilde 500 $\mu $m heat flux width for ITER. We find \textasciitilde 50{\%} scatter around the inverse-$B_{\mathrm{p}}$ scaling and are searching for the `hidden variables' causing this scatter. Supported by USDoE award DE-FC02-99ER54512.