Vacuum Compatability of Welded Joints for NSTX-U
Authors: M. Denault and D. Arose
Abstract:
The high vacuum environment of the National Spherical
Torus Experiment (NSTX) cannot tolerate a leak rate of greater than
1x10-5 Torr-liters per second or an out-gassing rate of more than
2x10-12 Torr-liters per second per cm2. This is maintained with an
austenitic 316 stainless steel vacuum vessel. The NSTX Upgrade
(NSTX-U) will require large weldments attached to the current
vacuum vessel that will become the new vacuum boundary. Due to
the lack of superstructure, all loads are passed through the vacuum
vessel. This means the welds must carry a substantial load as well as
provide vacuum integrity. Distortion of the vessel must also be
minimized in order to accommodate precisely-aligned diagnostics as
well as to mate to the new second neutral beam. The ideal candidate
for these welds is Flux Cored Arc Welding (FCAW). FCAW can
deposit a great amount of weld material quickly with minimal heat
input. This paper will discuss the vacuum compatibility of FCAW and
compare it to other standard welding processes used on NSTX.
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Submitted to: 38th International Conference on Plasma Science & 24th Symposium on Fusion Engineering/ICOPS 2011 SOFE, Chicago, IL, June 26-30, 2011
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Download PPPL-4666 (pdf 381 KB 3 pp)
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