title: Observation of a critical gradient threshold for electron temperature fluctuations in the DIII-D Tokamak.
abstract: A critical gradient threshold has been observed for the first time in a systematic, controlled experiment for a locally measured turbulent quantity in the core of a confined high-temperature plasma. In an experiment in the DIII-D tokamak where L(T(e))(-1) = |∇T(e)|/T(e) and toroidal rotation were varied, long wavelength (k(θ)ρ(s) ≲ 0.4) electron temperature fluctuations exhibit a threshold in L(T(e))(-1): below, they change little; above, they steadily increase. The increase in δT(e)/T(e) is concurrent with increased electron heat flux and transport stiffness. Observations were insensitive to rotation. Accumulated evidence strongly enforces the identification of the experimentally observed threshold with ∇T(e)-driven trapped electron mode turbulence.
authors.affiliation: Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Hillesheim
authors.affiliation: General Atomics, San Diego, California 92186-5608, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: DeBoo
authors.affiliation: Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA.
authors.forename: W A
authors.initials: WA
authors.lastname: Peebles
authors.affiliation: Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Carter
authors.affiliation: Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA.
authors.forename: G
authors.initials: G
authors.lastname: Wang
authors.affiliation: Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA.
authors.forename: T L
authors.initials: TL
authors.lastname: Rhodes
authors.affiliation: Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA.
authors.forename: L
authors.initials: L
authors.lastname: Schmitz
authors.affiliation: University of Wisconsin Madison, Madison, Wisconsin 53706-1687, USA.
authors.forename: G R
authors.initials: GR
authors.lastname: McKee
authors.affiliation: University of Wisconsin Madison, Madison, Wisconsin 53706-1687, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Yan
authors.affiliation: General Atomics, San Diego, California 92186-5608, USA.
authors.forename: G M
authors.initials: GM
authors.lastname: Staebler
authors.affiliation: General Atomics, San Diego, California 92186-5608, USA.
authors.forename: K H
authors.initials: KH
authors.lastname: Burrell
authors.affiliation: Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Doyle
authors.affiliation: University of California at San Diego, La Jolla, California 92093-0417, USA.
authors.forename: C
authors.initials: C
authors.lastname: Holland
authors.affiliation: General Atomics, San Diego, California 92186-5608, USA.
authors.forename: C C
authors.initials: CC
authors.lastname: Petty
authors.affiliation: General Atomics, San Diego, California 92186-5608, USA.
authors.forename: S P
authors.initials: SP
authors.lastname: Smith
authors.affiliation: Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: A E
authors.initials: AE
authors.lastname: White
authors.affiliation: Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA.
authors.forename: L
authors.initials: L
authors.lastname: Zeng