Very high‐ and high‐confinement mode limited discharges in DIII‐D

The first observations of marginally limited very high confinement mode (VH‐mode) discharges have been achieved in DIII‐D [Nucl. Fusion Special Supplement: World Survey of Activities in Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1990)] with significant reductions in peak heat flux conducted to plasma facing surfaces. In addition, quasistationary well limited high confinement‐mode (H‐mode) discharges have been obtained in DIII‐D, also with reduced peak heat flux. This demonstration of reduced peak heat flux while maintaining high performance, i.e., high energy confinement time, can be important for the design of fusion ignition devices. Energy confinement enhancements in these high triangularity discharges are comparable to diverted discharges with similar parameters: τE/τITER‐89P=2.9 for VH‐mode and τE/τITER‐89P=1.8 for quasistationary high confinement mode (H mode), where τITER‐89P is the empirically derived low confinement mode (L‐mode) energy confinement scaling relation [N...