Turbulence evolution and transport behavior during current ramp-up in ITER-like plasmas on DIII-D

Journal Article · 11 July 2017 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/aa78b8 · OSTI ID:1376861

McKee, George R. ^[1]; Austin, Max E. ^[2]; Boedo, Jose A. ^[3]; Bravenec, Ronald ^[4]; Holland, Christopher G. ^[3]; Jackson, Gary L. ^[5]; Luce, Timothy C. ^[5]; Rhodes, Terry L. ^[6]; Rudakov, Dimitry L. ^[3]; Wang, Guiding ^[6]; Yan, Zheng ^[7]; Zeng, Linjin ^[6]; Zhao, Yan ^[8]

---

1. Univ. of Wisconsin, Madison, WI (United States); General Atomics
2. Univ. of Texas, Austin, TX (United States)
3. Univ. of California San Diego, La Jolla, CA (United States)
4. Fourth State Research, Austin, TX (United States)
5. General Atomics, San Diego, CA (United States)
6. Univ. of California, Los Angeles, CA (United States)
7. Univ. of Wisconsin, Madison, WI (United States)
8. Univ. of Wisconsin, Madison, WI (United States); Soochow Univ., Jiangsu (People's Republic of China)

Low-wavenumber density fluctuations exhibit unique characteristics during the current ramp-up phase of ITER-like discharges that can partially explain the challenges of correctly modeling transport behavior and predicting global plasma parameters during this period. A strong interaction takes place between the evolving transport, safety factor (q) and kinetic profiles as well as the appearance and evolution of low-order rational surfaces. Density fluctuations from 0.75 < ρ < 0.9 are transiently reduced to exceptionally low levels during early times and from 0.8 < ρ < 0.9 at late times in the ramp-up in a manner that is different from behavior observed during steady-state plasma conditions with similar values of q₉₅. Turbulence is suppressed as low-order-rational q-surfaces enter the plasma; the local electron temperature likewise exhibits transient increases during these periods of reduced fluctuations indicating changes in transport that impact temperature and consequently the evolution of current density and plasma inductance. These observations can explain discrepancies between CORSICA modelling and the higher electron temperature found previously over the outer half radius. Comparison of turbulence properties with time-varying linear growth rates with GYRO and GENE demonstrate qualitative consistency with measured fluctuation levels, but calculations don’t exhibit reduced growth rates near low-order rational surfaces, which is inconsistent with experimental observations. Here, this indicates a mechanism that can contribute to reconciling observed turbulence behavior with transport models, allowing for the development of more accurate predictive tools.

• Research Organization: General Atomics, San Diego, CA (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE)
• Grant/Contract Number: FC02-04ER54698
• OSTI ID: 1376861
• Alternate ID(s): OSTI ID: 22925817
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 8 Vol. 57; ISSN 0029-5515
• Publisher: IOP ScienceCopyright Statement
• Country of Publication: United States
• Language: English