title: Suppression of electron temperature gradient turbulence via negative magnetic shear in NSTX.
abstract: Negative magnetic shear is found to suppress electron turbulence and improve electron thermal transport for plasmas in the National Spherical Torus Experiment (NSTX). Sufficiently negative magnetic shear results in a transition out of a stiff profile regime. Density fluctuation measurements from high-k microwave scattering are verified to be the electron temperature gradient (ETG) mode by matching measured rest frequency and linear growth rate to gyrokinetic calculations. Fluctuation suppression under negligible E×B shear conditions confirm that negative magnetic shear alone is sufficient for ETG suppression. Measured electron temperature gradients can significantly exceed ETG critical gradients with ETG mode activity reduced to intermittent bursts, while electron thermal diffusivity improves to below 0.1 electron gyro-Bohms.
authors.affiliation: Nova Photonics Inc., Princeton, New Jersey 08540, USA. hyuh@pppl.gov
authors.forename: H Y
authors.initials: HY
authors.lastname: Yuh
authors.forename: S M
authors.initials: SM
authors.lastname: Kaye
authors.forename: F M
authors.initials: FM
authors.lastname: Levinton
authors.forename: E
authors.initials: E
authors.lastname: Mazzucato
authors.forename: D R
authors.initials: DR
authors.lastname: Mikkelsen
authors.forename: D R
authors.initials: DR
authors.lastname: Smith
authors.forename: R E
authors.initials: RE
authors.lastname: Bell
authors.forename: J C
authors.initials: JC
authors.lastname: Hosea
authors.forename: B P
authors.initials: BP
authors.lastname: LeBlanc
authors.forename: J L
authors.initials: JL
authors.lastname: Peterson
authors.forename: H K
authors.initials: HK
authors.lastname: Park
authors.forename: W
authors.initials: W
authors.lastname: Lee