Momentum transport studies from multi-machine comparisons

ITPA Transport & Confinement Topical Group

    Research output: Contribution to journalArticleScientificpeer-review

    11 Citations (Scopus)

    Abstract

    A database of toroidal momentum transport on five tokamaks, Alcator C-Mod, DIII-D, JET, NSTX and JT-60U, has been constructed under a wide range of conditions in order to understand the characteristics of toroidal momentum transport coefficients, namely the toroidal momentum diffusivity (χ) and the pinch velocity (Vpinch). Through an inter-machine comparison, the similarities and differences in the properties of χ and Vpinch among the machines have been clarified. Parametric dependences of these momentum transport coefficients have been investigated over a wide range of plasma parameters taking advantage of the different operation regimes in machines. The approach offers insights into the parametric dependences as follows. The toroidal momentum diffusivity (χ) generally increases with increasing heat diffusivity (χi). The correlation is observed over a wide range of χ, covering roughly two orders of magnitude, and within each of the machines over the whole radius. Through the inter-machine comparison, it is found that χbecomes larger in the outer region of the plasma. Also observed is a general trend for Vpinch in tokamaks; the inward pinch velocity (−Vpinch) increases with increasing χ. The results that are commonly observed in machines will support a toroidal rotation prediction in future devices. On the other hand, differences among machines have been observed. The toroidal momentum diffusivity, χ, is larger than or equal to χi in JET and JT-60U; on the other hand, χ is smaller than or equal to χiin NSTX, DIII-D and Alcator C-Mod. In DIII-D, the ratio −RVpinch/χ at r/a = 0.5–0.6 is about 2, which is small compared with that in other tokamaks (−RVpinch/χ ≈ 5). Based on these different observations, parametric dependences of χ/χi, RVpinch/χ and χ have been investigated in H-mode plasmas. Across the dataset from all machines, the ratio χ/χi tends to be larger in low  at fixed Te/Ti and . An increase in χ is observed with decreasing ne and/or increasing Te. The pinch number (−RVpinch/χ) is observed to increase with increasing  at both q95 = 5.5–7.2 and q95 = 3.7–4.5. Here , , Te, Ti,  and q95 are, respectively, the normalized effective electron collision frequency, the normalized ion poloidal Larmor radius, the electron and ion temperatures, the inverse ratio of density scale length, , to the major radius, R, and the safety factor at the 95% flux surface.
    Original languageEnglish
    Article number123005
    JournalNuclear Fusion
    Volume52
    Issue number12
    DOIs
    Publication statusPublished - 2012
    MoE publication typeA1 Journal article-refereed

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