Speaker
Mr
John Canik
(Oak Ridge National Laboratory)
Description
The application of lithium coatings to the plasma-facing components (PFCs) of the National Spherical Torus Experiment (NSTX) has been shown to strongly impact plasma performance, improving energy confinement and eliminating ELMs. The pedestal structure is strongly affected by lithium: in discharges with lithium coatings, the density pedestal widens, and the electron temperature (Te) gradient increases inside a radius of N~0.95, but is unchanged for N >0.95. Interpretive 2-D plasma/neutrals modeling has been performed for pre-lithium and with-lithium discharges. The modeling indicates that the application of lithium to the PFC surfaces reduces R from ~0.98 to 0.9. The inferred effective electron thermal (eeff) and particle (Deeff) profiles reflect the profile changes: eeff is similar in the near-separatrix region, and is reduced in the region N < 0.95 in the with-lithium case. The Deeff profile shows a broadening of the region with low diffusivity with lithium, while the minimum value within the steep gradient region is comparable in the two cases. The linear microstability properties in the near-separatrix and pedestal-top regions have been analyzed. At N=0.88, low-k (ks < 1) microinstabilities are unstable, with the dominant modes being ITG-like in the pre-lithium case and TEM-like with lithium. The radial electric field shearing rate at this location increases with lithium, becoming significant compared to the maximum linear growth rate. In the region N>0.95, both the pre- and with-lithium cases are calculated to be strongly unstable to ETG modes, and are also both found to lie near the onset for kinetic ballooning modes.
Country or International Organization of Primary Author
USA
Primary author
Mr
John Canik
(Oak Ridge National Laboratory)
Co-authors
Dr
Benoit LeBlanc
(PPPL)
Dr
Henry Kugel
(PPPL)
Dr
Rajesh Maingi
(Oak Ridge National Laboratory)
Dr
Ron Bell
(PPPL)
Dr
Shigeyuki Kubota
(UCLA)
Dr
Tom Osborne
(GA)
Dr
Vsevolod Soukhanovskii
(Lawrence Livermore National Laboratory)
Dr
Walter Guttenfelder
(Princeton Plasma Physics Laboratory)
Dr
Yang Ren
(Princeton Plasma Physics Laboratory)
