Observation of a critical gradient threshold for electron temperature fluctuations in the DIII-D Tokamak

• Published in: Physical review letters 2013-01, Vol.110 (4), p.045003-045003, Article 045003
• Main Authors: Hillesheim, J C, DeBoo, J C, Peebles, W A, Carter, T A, Wang, G, Rhodes, T L, Schmitz, L, McKee, G R, Yan, Z, Staebler, G M, Burrell, K H, Doyle, E J, Holland, C, Petty, C C, Smith, S P, White, A E, Zeng, L
• Format: Article
• Language: English
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/physrevlett.110.045003

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.