Role of turbulence regime on determining the local density gradient

Journal Article · Thu Nov 16 00:00:00 EST 2017 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/aa92a0· OSTI ID:1420327

Wang, X. ^[1]; Mordijck, Saskia ^[1]; Doyle, E. J. ^[2]; Zeng, L. ^[2]; Staebler, Gary M. ^[3]; Meneghini, Orso ^[3]; Smith, Sterling P. ^[3]

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1. College of William and Mary, Williamsburg, VA (United States)
2. Univ. of California, Los Angeles, CA (United States)
3. General Atomics, San Diego, CA (United States)

In this study we show that the local density gradient in the plasma core depends on the calculated mode-frequency of the most unstable linear mode and reaches a maximum when this frequency is close to zero. Previous theoretical and experimental work on AUG has shown that the ratio of electron to ion temperature, and as such the frequency of the dominant linear gyrokinetic mode, affects the local density gradient close to ρ = 0.3 [1, 2]. On DIII-D we find that by adding Electron Cyclotron Heating (ECH), we modify the dominant unstable linear gyro kinetic mode from an Ion Temperature Gradient (ITG) mode to a Trapped Electron Mode (TEM), which means that the frequency of the dominant mode changes sign (from the ion to the electron direction). Local density peaking around mid-radius increases by 50% right around the cross-over between the ITG and TEM regimes. By comparing how the particle flux changes, through the derivative of the electron density, n_e, with respect to time, ∂n_e/∂t, we find that the particle flux also exhibits the same trend versus mode frequency. As a result, we find that the changes in local particle transport are inversely proportional to the changes in electron density, indicating that the changes are driven by a change in thermo-diffusive pinch.

• Research Organization: General Atomics, San Diego, CA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: FC02-04ER54698
• OSTI ID: 1420327
• Journal Information: Nuclear Fusion, Vol. 58, Issue 1; ISSN 0029-5515
• Publisher: IOP Science
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
transport
turbulence
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