Transport Variations in High qmin>1.5 Plasmas with Heating and Current Drive Actuators

K.E. Thome, J.R. Ferron, C.C. Petty, B.S. Victor, C.T. Holcomb, E. Schuster, W. Wehner, J.M. Park, B.A. Grierson, F.M. Poli

Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)

Portland, OR, USA, November 5-9, 2018

`Predict-first' methodology was employed to develop an experimental plan on DIII-D to study the effect of heating and current drive actuators on the current and pressure profiles of high-qmin>1.5, βN>3 plasmas, with the goal of achieving stable unchanging Vloop profiles as early in the discharge as possible to avoid the appearance of deleterious tearing modes. Predictive transport modeling conducted with TGLF in TRANSP indicated how varying the Ip ramp rate, ECCD timing, and NBI timing would change these profiles. During the experiment, qmin>2 discharges were sustained and their tearing instability, qmin, and performance was altered by these actuators. Changing the Ip ramp rate had little effect on the discharge but applying ECCD and/or NBI earlier increased qmin and improved n=2 tearing stability. TGLF predicted the effect of ECCD but not the other results. Increased fast-ion transport was also observed. Comparison of pre-experiment modeling, experimental results including turbulence data, and post-experiment simulations will be discussed in detail. These results will be used to validate transport models in this regime and to prepare for the upcoming 2019 campaign when increased off-axis co-Ip NBI power will be available.