Studies in DIII-D of High Beta Discharge Scenarios Appropriate for Steady-state Tokamak Operation With Burning Plasmas

In the DIII-D steady-state scenario with $q_{min} =\,$1.5-2.0, the duration with the noninductive current fraction ($f_{NI}$) near 1 has been extended to 70\% of the resistive time. To extend duration, ECCD is deposited with a broad profile in order to avoid the 2/1 tearing mode, enabling reliable operation at $\beta_N =\,$3.6-3.7. These discharges have double-null shape biased in the direction opposite the $\nabla B$ drift, in order to simultaneously optimize confinement and divertor pumping, and ECCD power up to 3~MW. An alternate scenario with internal inductance increased to 1.1-1.4 is under study, motivated by the possibility of steady-state operation at $\beta_N=\,$4-5 without wall stabilization. Thus far, $\beta_N=\,$4.6, just below the calculated $n=1$ and $n =\infty$ stability limits, has been achieved transiently with $f_{NI} = 0.85$.