Predictive modeling of high $\beta$ DIII-D plasmas

Predictive modeling tools are used to test the effects of various actuators and plasma parameters in order to optimize the development and sustainment of high $\beta_N$ discharges on DIII-D. Two discharges are used as starting points for this modeling: 1. A high q$_{min}$ shot with $\beta_N \sim 3.5$, q$_{min} > 2$, and q$_{95} \sim 6.1$; 2. A hybrid shot with $\beta_N \sim 3.7$, q$_{min} \sim 1$, and q$_{95} \sim 5.6$. For the high q$_{min}$ discharge, the goal is to understand how to best utilize additional heating and current drive actuators, such as electron cyclotron heating (ECH), to increase beta and improve stability. Predictive modeling is performed using TGLF in TRANSP over several seconds of shot time. The density and temperature profiles are fixed in the pedestal region and TGLF models the evolution of T$_e$, T$_i$, and ne based on the plasma and current drive actuators. Results of these simulations show that additional ECH power broadens the current density profile and increases the ideal-wall stability limits. For the hybrid discharge, a single time slice during the high confinement portion of the shot (H$_{98y2} \sim 2$) is analyzed in detail using TGYRO. The rotation profile is scaled to separate the effects of rotation and pedestal height on confinement. These rotation scans will then be performed experimentally in the future by varying the ratio of co- and counter-Ip neutral beam current drive.