Stationary I-modes in multiple configurations in the DIII-D tokamak

By using β feedback to compensate for improving τ_E, longer, more stationary I-modes were obtained than in past DIII-D experiments. These experiments were conducted as part of the 2022 Joint Research Target campaign on intrinsically non-ELMing enhanced confinement regimes. I-modes feature a temperature pedestal but low particle confinement. Configurations tested were a LSN, low triangularity δ shape matching an ASDEX Upgrade I-mode discharge and a higher δ USN shape with better pumping in the closed divertor. Both had B×∇B drifts away from the X-point, as usual for I-mode. In the LSN shape, the upper limit for heating power (3.5 MW) and pressure (β_N=1) was set by I-H transitions. In the USN shape, it was limited by available power (11 MW NBI) and β_N as high as1.6 was achieved. T_e and T_i pedestals formed in both configurations, with negligible changes in density from L-mode. The Weakly Coherent Mode has not yet been identified in these discharges; further analysis is ongoing. Many other turbulence and fluctuations changes were observed, including a reduction of density fluctuations at intermediate k, a decrease of magnetic turbulence at 100-500 kHz, and bursts of n~20 MHD in T_e on ECE Imaging.