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The effect of lithium surface coatings on plasma performance in the National Spherical Torus Experimenta)
a)Paper TI2 6, Bull. Am. Phys. Soc. 52, 276 (2007).
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View: Figures


Image of FIG. 1.
FIG. 1.

Shown is a schematic diagram of the poloidal cross section of NSTX, the locations of the lithium evaporator (LITER) at toroidal angle , and the aiming angles used for the 2006 and 2007 campaigns, respectively. Shown also are the two quartz deposition monitors, each at toroidal angle , used as independent monitors of the lithium deposition rate as determined from the oven temperature. The red line indicates the LCFS of the LSND deuterium reference discharges used for the LITER campaigns.

Image of FIG. 2.
FIG. 2.

Schematic diagram of the lithium evaporator (2007-LITER).

Image of FIG. 3.
FIG. 3.

The results of a typical laboratory angular distribution measurement of the output lithium beam at using a scanning quartz deposition monitor. The measured angular distributions were found to be independent of temperature over the temperature range .

Image of FIG. 4.
FIG. 4.

Simulation of the evaporated lithium distribution over the NSTX lower divertor region showing the relative change in deposition thickness over the lower divertor region. Shown are the locations of the divertor viewports at each of the 12 bays, the locations of midplane coupons, and the divertor tiles used to compare the deposition simulation with results from nuclear reaction analysis.

Image of FIG. 5.
FIG. 5.

A comparison of the density profiles for the reference deuterium discharge before lithium (black) and the first deuterium reference discharge immediately after LPI deposition of (red). A reduction in the volume-averaged density by a factor of about 2 and profile shape changes occurred. The profile measurement times for both discharges are (solid), (longer dashes), (shorter dashes).

Image of FIG. 6.
FIG. 6.

The 2007 database of electron stored energy vs total stored energy for deuterium reference plasmas immediately following lithium deposition, and for deuterium reference plasmas prior to lithium deposition. EFIT02 is an equilibrium analysis constrained by external magnetics, electron profile shape, and diamagnetic flux.

Image of FIG. 7.
FIG. 7.

Shown for the same discharges as in Fig. 6, are (a) the central electron temperature vs the volume-averaged electron temperature , and (b) the central density vs the volume-averaged electron density .

Image of FIG. 8.
FIG. 8.

Shown for the same discharges as in Fig. 6, is the central ion temperature vs the volume-averaged ion temperature obtained by assuming the same density distribution as the electrons.

Image of FIG. 9.
FIG. 9.

Comparison of examples of (a) electron transport coefficients and (b) ion transport coefficients derived, respectively, using the time dependent transport code TRANSP for a quiescent interval in a discharge following lithium deposition with the same interval in a prior to lithium deposition discharge.

Image of FIG. 10.
FIG. 10.

Shown for deuterium reference discharges before and after Li deposition are (a) the total electron density and NB fueling waveforms and (b) the early density profiles at . Significant initial D pumping was exhibited at plasma start-up, at higher Li evaporation rates . Prior to these discharges, typical Li evaporation rates of were used.

Image of FIG. 11.
FIG. 11.

Shown for two deuterium reference discharges before and after Li deposition are (a) the total electron density, (b) the stored energy, (c) before Li, (d) after Li, (e) density profile , (f) electron temperature profile , and (g) the ion temperature profile . After Li deposition the stored energy increased (b) and the occurrence of large ELMs was greatly reduced (d). Note the quiescent period exhibited in the edge luminosity (d) in the interval .

Image of FIG. 12.
FIG. 12.

The lower divertor , C II, and O II luminosity decreased with increasing total accumulating lithium deposited on PFCs during the run day.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: The effect of lithium surface coatings on plasma performance in the National Spherical Torus Experimenta)