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Snowflake divertor configuration studies in National Spherical Torus Experimenta)
a)Paper BAPS.2010.DPP.JI2.2, http://meetings.aps.org/link/BAPS.2010.DPP.JI2.2.
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View: Figures


Image of FIG. 1.
FIG. 1.

Poloidal flux contours in the standard (a) and the asymmetric snowflake-minus (b) divertor configurations. Shown are separated by 3 mm in the mid-plane. Poloidal magnetic field distribution in the standard (c) and snowflake (d) configurations. Visualization of the field line on the flux surface in the standard divertor (e) and the snowflake divertor (f).

Image of FIG. 2.
FIG. 2.

Time histories of (a) plasma current ; divertor coil currents (b) PF1A; (c) PF1B; (d) PF2L; and (e) X-point flux expansion in the standard divertor (black lines) discharge and the SFD (red lines) discharge.

Image of FIG. 3.
FIG. 3.

Examples of SFD-minus configuration failure modes on NSTX. (a) Poloidal field nulls too far; (b) poloidal field null positions too close to divertor plate leading to separatrix touching the PFC; (c) null orientation distorted leading to poloidal flux reconnection and a transient SFD-plus; (d) further motion of secondary null inward from (c) leading to an additional SOL line reconnection and a formation of the SFD-minus in the inner leg.

Image of FIG. 4.
FIG. 4.

Time histories of core and edge plasma quantities in the standard divertor (black traces) and the SFD (red): (a) Averaged density ; (b) Central electron temperature ; (c) Normalized ; (d) Core plasma stored energy ; and (e) Lower divertor total Dα intensity.

Image of FIG. 5.
FIG. 5.

Time histories of core and edge impurity quantities in the standard divertor (black traces) and the SFD (red): (a) Total plasma ; (b) Central carbon density ; (c) Pedestal carbon density ; and (d) Near-separatrix C III density.

Image of FIG. 6.
FIG. 6.

Time evolution of plasma profiles, carbon density (, first column), carbon concentration ( second column), carbon ion temperature (, third column), and deuterium ion density (, forth column), in the standard divertor discharge (black traces) and the SFD discharge (red) at the four times before and during the SFD formation, as discussed in Sec. III B.

Image of FIG. 7.
FIG. 7.

Contour plots of divertor heat flux as a function of time and divertor R in the standard divertor (a) and SFD (b). CHI gap is a physical gap between divertor target plates where infrared thermography measurements cannot be performed.

Image of FIG. 8.
FIG. 8.

Time histories of divertor quantities in the standard divertor (black traces) and the SFD (red) discharges: (a) divertor heating power ; (b) divertor bolometer vertical chord signal (viewing geometry shown in inset); (c) divertor C II intensity; (d) divertor pressure; (e) Balmer n = 6-2 line intensity in the strike point region and in the periphery of the high flux expansion zone .

Image of FIG. 9.
FIG. 9.

Visible color camera images of entire NSTX plasmas: top panels—the standard divertor discharge (a)–(d), bottom panels (e)–(h)—the SFD discharge. Images are representative of the times discussed in the text: 0.360 s—(a) and (e); 0.570 s—(b) and (f); 0.700 s—(c) and (g); and 0.895 s—(d) and (h).

Image of FIG. 10.
FIG. 10.

Divertor profiles at different times of the SFD discharge (a) heat flux; (b) C III brightness; and (c) C IV brightness.

Image of FIG. 11.
FIG. 11.

Lower divertor surface temperature (upper panels) and magnetic field incidence angle γ (bottom panels) in the SFD discharge at the times (a) before the SFD formation—0.360 s; forming SFD—(b) 0.570 s and (c) 0.700 s; and (d) radiative SFD—0.895 s. The dashed line in the bottom panels shows the standard divertor angle γ at t = 0.360 s from (a) for comparison.

Image of FIG. 12.
FIG. 12.

Initial UEDGE model results of the standard divertor (black lines) and SFD (red lines): (a) and (b) divertor region computation mesh; divertor plate profiles: (c) , (d) heat flux ; and (e) particle flux .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Snowflake divertor configuration studies in National Spherical Torus Experimenta)