Results from experiments on DIII-D [J. L. Luxon, Fusion Sci. Technol. 48, 828 (2005)] aimed at developing high steady-state operating scenarios with high- confirm that fast-ion transport is a critical issue for advanced tokamak development using neutral beam injection current drive. In DIII-D, greater than 11 MW of neutral beam heating power is applied with the intent of maximizing and the noninductive current drive. However, in scenarios with that target the typical range of 5–7 used in next-step steady-state reactor models, Alfvén eigenmodes cause greater fast-ion transport than classical models predict. This enhanced transport reduces the absorbed neutral beam heating power and current drive and limits the achievable βN. In contrast, similar plasmas except with just above 1 have approximately classical fast-ion transport. Experiments that take plasmas to higher with 11–12 for testing long pulse operation exhibit regimes of better than expected thermal confinement. Compared to the standard high- scenario, the high cases have shorter slowing-down time and lower , and this reduces the drive for Alfvénic modes, yielding nearly classical fast-ion transport, high values of normalized confinement, , and noninductive current fraction. These results suggest DIII-D might obtain better performance in lower-, high- plasmas using broader neutral beam heating profiles and increased direct electron heating power to lower the drive for Alfvén eigenmodes.
This material was based upon work supported in part by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Award Nos. DE-FC02-04ER54698, DE-AC52-07NA27344, SC-G903402, DE-AC02-09CH11466, DE-AC05-00OR22725, and DE-FG02-04ER54761. DIII-D data shown in this paper can be obtained in digital format by following the links at https://fusion.gat.com/global/D3D_DMP.
I. INTRODUCTION II. COMPARISON OF HIGH- AND LOW- DISCHARGES HAVING 5–7 III. HIGH WITH HIGH IV. FUTURE OUTLOOK V. SUMMARY