Transition to ELM-free improved H-mode by lithium deposition on NSTX graphite divertor surfaces

Mansfield, D.K.; Kugel, H.; Maingi, R.; Bell, M.G.; Bell, R.E.; Kaita, R.; Kallman, J.; Kaye, S. M.; LeBlanc, B.P.; Mueller, D.; Paul, S. F.; Raman, R.; Roquemore, L.; Sabbagh, S.A.; Schneider, H.; Skinner, C.H.; Soukhanovskii, V.; Timberlake, J.; Wilgen, J. B.; Zakharov, L.

doi:10.1016/j.jnucmat.2009.01.203

Cited by 74 publications

(47 citation statements)

References 27 publications

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“…As a result of the pumping effect of the lithium coating, the level of deuterium Balmer-alpha emission from a chord viewing the lower divertor is significantly reduced, despite increasing the gas fueling rate to maintain the plasma density. There is an almost complete suppression of ELMs in the discharge with lithium, although the plasma remains in the H-mode [16]. Although not shown here, the line emission from lowionization states of oxygen and carbon measured by instruments viewing the lower divertor were also lower following the introduction of lithium.…”

Section: Lithium Coating Techniques and Their Effects In Nstxmentioning

confidence: 56%

Plasma response to lithium-coated plasma-facing components in the National Spherical Torus Experiment

Bell

Kugel

Kaita

et al. 2009

Plasma Phys. Control. Fusion

132

110

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Experiments in the National Spherical Torus Experiment (NSTX) have shown beneficial effects on the performance of divertor plasmas as a result of applying lithium coatings on the graphite and carbonfiber-composite plasma-facing components. These coatings have mostly been applied by a pair of lithium evaporators mounted at the top of the vacuum vessel which inject collimated streams of lithium vapor towards the lower divertor. In NBI-heated, deuterium H-mode plasmas run immediately after the application of lithium, performance modifications included decreases in the plasma density, particularly in the edge, and inductive flux consumption, and increases in the electron and ion temperatures and the energy confinement time. Reductions in the number and amplitude of ELMs were observed, including complete ELM suppression for periods up to 1.2 s, apparently as a result of altering the stability of the edge. However, in the plasmas where ELMs were suppressed, there was a significant secular increase in the effective ion charge Z eff and the radiated power as a result of increases in the carbon and medium-Z metallic impurities, although not of lithium itself which remained at a very low level in the plasma core, <0.1%. The impurity buildup could be inhibited by repetitively triggering ELMs with the application of brief pulses of an n = 3 radial field perturbation. The reduction in the edge density by lithium also inhibited parasitic losses through the scrape-off layer of ICRF power coupled to the plasma, enabling the waves to heat electrons in the core of H-mode plasmas produced by NBI. Lithium has also been introduced by injecting a stream of chemically stabilized, fine lithium powder directly into the scrape-off layer of NBI-heated plasmas. The lithium was ionized in the SOL and appeared to flow along the magnetic field to the divertor plates. This method of coating produced similar effects to the evaporated lithium but at lower amounts.

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Section: Lithium Coating Techniques and Their Effects In Nstxmentioning

confidence: 56%

Plasma response to lithium-coated plasma-facing components in the National Spherical Torus Experiment

Bell

Kugel

Kaita

et al. 2009

Plasma Phys. Control. Fusion

132

110

View full text Add to dashboard Cite

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“…The observed reduction was attributed to the reduction of carbon physical sputtering fluxes in the SF divertor (due to very low divertor T e ), and to the particle expulsion effect from ELMs that appeared in the SF phase [20]. In the standard divertor Hmode discharge, lithium coatings on lower divertor PFCs reduced recycling and led to modified edge plasma pressure and current profiles and low-n peeling-ballooning mode stabilization [26,27], as the pedestal stability op- close to the kink-balooning stability boundary, and the SF-plus configuration was consistent with improved kink-ballooning stability [23,24,28]. Equilibria reconstructions also confirmed a higher magnetic shear inside the separatrix in the SF-plus phase.…”

Section: Resultsmentioning

confidence: 99%

Advanced divertor configurations with large flux expansion

Soukhanovskii

Bell

Diallo

et al. 2013

Journal of Nuclear Materials

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Experimental studies of the novel snowflake divertor concept (D. Ryutov, Phys. Plasmas 14, 064502 (2007)) performed in the NSTX and TCV tokamaks are reviewed in this paper. The snowflake divertor enables power sharing between divertor strike points, as well as the divertor plasma-wetted area, effective connection length and divertor volumetric power loss to increase beyond those in the standard divertor, potentially reducing heat flux and plasma temperature at the target. It also enables higher magnetic shear

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“…As a point of interest, the two-color technique seems to enhance filamentary heating from ELM filaments. In much of the data from 2010, the plasma was operated in an ELM-free mode, because of the tendency of lithium to reduce the density profile and suppress ELMs [29][30][31][32] . In ELM-free discharges, there is no sign of filaments in the two-color data, demonstrating that the filament images are not an artifact of this technique.…”

Section: N2 Diagnostic Preparationsmentioning

confidence: 99%