Observation of trapped-electron-mode microturbulence in reversed field pinch plasmas

Duff, J. R.; Williams, Z. R.; Brower, D. L.; Chapman, B. E.; Ding, W. X.; Pueschel, M. J.; Sarff, J. S.; Terry, P. W.

doi:10.1063/1.5010198

Title: Observation of trapped-electron-mode microturbulence in reversed field pinch plasmas

Journal Article · 29 December 2018 · Physics of Plasmas

DOI: https://doi.org/10.1063/1.5010198 · OSTI ID:1524582

^[1];

^[1]; Brower, D. L. ^[2];

^[1]; Ding, W. X. ^[2]; Pueschel, M. J. ^[1]; Sarff, J. S. ^[1]; Terry, P. W. ^[1]

Univ. of Wisconsin, Madison, WI (United States). Dept. of Physics
Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy

Density fluctuations in the large-density-gradient region of improved confinement Madison Symmetric Torus reversed field pinch (RFP) plasmas exhibit multiple features that are characteristic of the trapped-electron mode (TEM). Core transport in conventional RFP plasmas is governed by magnetic stochasticity stemming from multiple long-wavelength tearing modes. Using inductive current profile control, these tearing modes are reduced, and global confinement is increased to that expected for comparable tokamak plasmas. Under these conditions, new short-wavelength fluctuations distinct from global tearing modes appear in the spectrum at a frequency of f ~ 50 kHz, which have normalized perpendicular wave numbers k_⊥ρ_s≲0.2 and propagate in the electron diamagnetic drift direction. They exhibit a critical-gradient threshold, and the fluctuation amplitude increases with the local electron density gradient. These characteristics are consistent with predictions from gyrokinetic analysis using the Gene code, including increased TEM turbulence and transport from the interaction of remnant tearing magnetic fluctuations and zonal flow.

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Research Organization:: Univ. of Wisconsin, Madison, WI (United States); Univ. of California, Los Angeles, CA (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE

Grant/Contract Number:: FC02-05ER54814; FG02-01ER54615

OSTI ID:: 1524582

Alternate ID(s):: OSTI ID: 1415156

Journal Information:: Physics of Plasmas, Vol. 25, Issue 1; ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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