Toroidal asymmetries in divertor impurity influxes in NSTX

Scotti, F.; Soukhanovskii, V.; Ahn, J.-W.; McLean, A.G.; Kaita, R.

doi:10.1016/j.nme.2017.03.037

Cited by 2 publications

(1 citation statement)

References 17 publications

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“…Lithium erosion at the divertor plate was found to be consistent with physical and temperature-enhanced erosion [157] while the application of lithium on graphite plasma facing components led to a moderate reduction in carbon sputtering. Toroidal asymmetries in divertor impurity influxes were found to be due to leading edges of divertor tiles (for carbon) and the toroidally asymmetric deposition from the lithium wall conditioning evaporators (for lithium) [158]. The latter toroidal asymmetries, in particular, could lead to inaccuracies in determining the total source of lithium impurities.…”

Section: Particle Transportmentioning

confidence: 99%

Thermal confinement and transport in spherical tokamaks: a review

Kaye¹,

Connor²,

Roach³

2021

Plasma Phys. Control. Fusion

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In this paper, we review the thermal plasma confinement and transport properties observed and predicted in low aspect ratio tokamaks, or spherical tokamaks (STs), which can depart significantly from those observed at higher aspect ratio. In particular, thermal energy confinement scalings show a strong, near linear dependence of energy confinement time on toroidal magnetic field, while the dependence on plasma current is more modest, the opposite of what is seen at higher aspect ratio. STs have revealed a very strong improvement in normalized confinement with decreasing collisionality, much stronger than at higher aspect ratio, which bodes well for an ST-based fusion pilot plant should this trend continue at an even lower collisionality than has already been accessed. These differences arise because of fundamental differences in transport in STs due to the more extreme toroidicity (i.e. reduced region of bad curvature), and to the relatively larger E r × B shearing rates, both of which can suppress electrostatic drift wave instabilities at both ion and electron gyroradius scales. In addition, electromagnetic effects are much stronger in STs because they operate at high β T . Gyrokinetic (GK) studies, coupled with low- and high-k turbulence measurements, have shed light on the underlying physics controlling transport. At lower β T , both ion- and electron-scale electrostatic drift turbulence may be responsible for transport. At higher βT , microtearing, kinetic ballooning, and hybrid trapped electron/kinetic ballooning modes increasingly play a role, and they have a much stronger impact in the core of ST plasmas than at higher aspect ratio. Flow shear affects the balance between ion- and electron-scale modes. Non-linear GK simulations find regimes where the electron heat flux decreases with decreasing collisionality, consistent with the experimental global normalized confinement scaling. The ST is unique in that the relatively low toroidal magnetic field allows for localized measurements of electron-scale turbulence, and this coupled with turbulence measurements at ion-scales has facilitated detailed comparisons with GK simulations. These data have provided compelling evidence for the presence of ion temperature gradient and electron temperature gradient turbulence in some plasmas, and direct experimental support for the impact of experimental actuators like rotation shear, density gradient and magnetic shear on turbulence and transport.

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Section: Particle Transportmentioning

confidence: 99%

Thermal confinement and transport in spherical tokamaks: a review

Kaye¹,

Connor²,

Roach³

2021

Plasma Phys. Control. Fusion

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MHD-blob correlations in NSTX

Zweben

Myra

et al. 2020

Physics of Plasmas

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This paper describes a study of the cross-correlations between edge fluctuations as seen in the gas puff imaging (GPI) diagnostic and low frequency coherent magnetic fluctuations (MHD) in H-mode plasmas in NSTX. The main new result was that large blobs in the scrape-off-layer were significantly correlated with MHD activity in the 3–6 kHz range in 21 of the 223 shots examined. There were also many other shots in which fluctuations in the GPI signal level and its peak radius Rpeak were correlated with MHD activity but without any significant correlation of the MHD with large blobs. The structure and motion of the MHD are compared with those of the correlated blobs, and some possible theoretical mechanisms for the MHD-blob correlation are discussed.

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Toroidal asymmetries in divertor impurity influxes in NSTX

Cited by 2 publications

References 17 publications

Thermal confinement and transport in spherical tokamaks: a review

Thermal confinement and transport in spherical tokamaks: a review

MHD-blob correlations in NSTX

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