PPPL-4891
Modification of the NSTX-U Outboard and Inboard Divertor Tiles for the Protection of the PF-1C Coils
Authors: K. Tresemer, S. Gerhardt, A. Brooks, A. Jariwala, R. Raman, P. Titus
Abstract:
The National Spherical Torus Experiment (NSTX) is
a low aspect ratio, spherical torus (ST) located at the Princeton
Plasma Physics Laboratory (PPPL). Its Centerstack Assembly
(CSA) consists of the inner legs of the Toroidal Field windings, the
Ohmic Heating solenoid, the inner Poloidal Field (PF) coils,
thermal insulation, diagnostics, and an Inconel casing which forms
the inner wall of the vacuum vessel boundary. The outside surface
of this casing is protected from the heat loads by a layer of Plasma
Facing Components (PFCs), in this case, a combination of ATJ
and POCO TM graphite. The CSA is electrically isolated from the
outer, large major radius part of the vacuum chamber by ceramic
insulators. The gaps at the top and bottom of the machine between
the CSA and the outer vessel are known as the "Coaxial Helicity
Injection (CHI) Gaps". The PF-1C divertor coils are located in this
region shadowed by the CHI gap, however, late in the design of the
NSTX Upgrade PFCs, MHD equilibria were discovered which
could direct field lines through these CHI gaps and onto the PF-1C
stainless steel casings. This could result in thermal flux from the
main plasma body to flow along the field lines directly onto the coil.
Though the probability of such an event is low, the heat flux on the
0.125" thick stainless steel casing could damage the coil beneath,
or in worst case, rupture the casing itself, resulting in an accidental
vent of the vacuum vessel. By extending downward the overhanging
edge of the row 1 PFCs on the Outboard Divertor (OBD) and the
Inboard Divertor (IBD) and by increasing their outermost radii,
effectively narrowing the CHI gap, this should provide significant
protection to the PF-1C casing.
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Submitted to: SOFE 2013 Proeedings (June 0213) 25th Symposium on Fusion Engineering, San Francisdco, CA (June 10-14, 2013)
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Download PPPL-4891 (pdf 1.7 MB 3 pp)
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