Improving Fast-Ion Confinement by Reducing Alfv\'{e}n Eigenmodes in the qmin\textgreater 2 Steady-State Tokamak Scenario

Experiments in the DIII-D tokamak show that a broadened fast-ion pressure profile enables better control of Alfv\'{e}n Eigenmodes (AEs), improves fast-ion confinement, and allows access to new regimes with 15{\%} higher normalized plasma beta ($\beta_{\mathrm{N}})$ than previously achieved in high-field, steady-state scenarios with negative central shear and q$_{\mathrm{min}}$\textgreater 2. Reversed Shear Alfv\'{e}n Eigenmodes (RSAEs) were reduced in the current ramp by increasing the off-axis neutral beam power fraction, resulting in $\sim $24{\%} higher ratio of measured neutrons to calculated classical neutrons. The neutron fraction was further improved using Electron Cyclotron Current Drive aimed on-axis, which suppressed RSAEs by moving the q$_{\mathrm{min}}$ location inward toward reduced beam pressure gradient and higher plasma pressure, resulting in a $\sim $36{\%} higher neutron ratio than the reference shot. In flattop, fast-ion confinement improved by $\sim $25{\%} after reducing beam pressure gradient (thus AE drive) by increasing the off-axis beam power fraction from 30{\%} to 70{\%}. Record parameters were achieved by increasing the relative density, reaching $\beta_{\mathrm{N}}\sim $3.1 and H$_{\mathrm{89}}\sim $2.3 at B$_{\mathrm{T}}=$2.0 T and q$_{\mathrm{95}}=$6.0. These experiments mark significant progress in understanding potential optimized regimes for steady-state advanced tokamaks that can avoid AE-induced fast-ion redistribution, loss, reduced heating efficiency, and limits to the achievable $\beta_{\mathrm{N}}$.