Progress towards sustainment of advanced tokamak modes in DIII-D

Improving confinement and beta limits simultaneously in long-pulse ELMy H-mode discharges is investigated. The product {beta}{sub N}H{sub 98y} serves as a useful figure-of-merit for performance, where {beta}{sub N} {triple_bond} {beta}/(I/aB) and H{sub 98y} is the ratio of the thermal confinement time relative to the most recent ELMy H-mode confinement scaling established by the ITER confinement database working group. In discharges with q{sub 0} {approximately} 1 (no sawteeth) and discharges with q{sub min} > 1.5 and negative central magnetic shear, {beta}{sub N} {approximately} 2.9 and H{sub 98y} {approximately} 1.4 are sustained for up to 2 s. Although peaked profiles are observed, steep internal transport barriers are not present. Further increases in {beta}{sub N} in these discharges is limited by neoclassical tearing modes (NTM) in the positive shear region. In another recently developed regime, {beta}{sub N} {approximately} 3.8 and H{sub 98y} {approximately} 1.8 has been sustained during large infrequent ELMs in non-sawtoothing discharges with 1{sub 0} {approximately} 1. This level of performance is similar to that obtained in ELM-free regimes such as VH-mode. The limitation on {beta}{sub N} and pulse length in these discharges is also the onset of NTMs.