Stabilization of electron-scale turbulence by electron density gradient in national spherical torus experiment

• DOI: 10.1063/1.4936110
• Publication Date: 2015-12-04T18:53:35Z
• Authors: J. Ruiz Ruiz; Y. Ren; W. Guttenfelder; A. E. White; S. M. Kaye; B. P. Leblanc; E. Mazzucato; K. C. Lee; C. W. Domier; D. R. Smith; H. Yuh
• Keywords: Density gradient; Electron temperature

Theory and experiments have shown that electron temperature gradient (ETG) turbulence on the gyro-scale, k⊥ρe ≲ 1, can be responsible for anomalous thermal transport in NSTX. Electron scale (high-k) is diagnosed NSTX with a high-k microwave scattering system [D. R. Smith et al., Rev. Sci. Instrum. 79, 123501 (2008)]. Here we report stabilization effects of density electron-scale fluctuations set neutral beam injection heated H-mode plasmas. We found absence from measurements correlated large equilibrium gradient, which to consistent linear ETG modes due using analytical threshold F. Jenko al. [Phys. Plasmas 8, 4096 (2001)] gyrokinetic simulations GS2 [M. Kotschenreuther Comput. Phys. Commun. 88, 128 (1995)]. also observed power (when it exists) anti-correlated suggesting as nonlinear stabilizing mechanism. Higher gradients give rise lower values plasma frame frequency, calculated based Doppler shift measured fluctuations. Linear show higher reduce value real agreement experimental observation. Nonlinear high reduces heat flux stiffness, increases threshold, observations.