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National Spherical Torus Experiment (NSTX)
Torus Design, Fabrication and Assembly
James H. Chrzanowski, Charles Neumeyer, Philip Heitzenroeder, George Barnes, Mike Viola,
Princeton Plasma Physics Laboratory, Princeton, NJ 08543 USA, Brad Nelson, Paul Gorenson, Oak
Ridge National Laboratory, Oak Ridge, Tn USA, and the NSTX Group *Abstract-The National Spherical Torus Experiment (NSTX)
is a low aspect ratio spherical torus (ST) located at Princeton
Plasma Physics Laboratory (PPPL). Fabrication, assembly,
and initial power tests were completed in February of 1999.
The majority of the design and construction efforts were
constructed on the Torus system components. The Torus
system includes the centerstack assembly, external Poloidal
and Toroidal coil systems, vacuum vessel, torus support
structure and plasma facing components (PFC's). NSTX's low
aspect ratio required that the centerstack be made with the
smallest radius possible. This, and the need to bake NSTX's
carbon-carbon composite plasma facing components at 350
degrees C, was major drivers in the design of NSTX.
The Centerstack Assembly consists of the inner legs of the
Toroidal Field (TF) windings, the Ohmic Heating (OH)
solenoid and its associated tension cylinder, three inner
Poloidal Field (PF) coils, thermal insulation, diagnostics and
an Inconel casing which forms the inner wall of the vacuum
vessel boundary. It took approximately nine months to
complete the assembly of the Centerstack. The tight radial
clearances and the extreme length of the major components
added complexity to the assembly of the Centerstack
components.
The vacuum vessel was constructed of 304-stainless steel and
required approximately seven months to complete and deliver
to the Test Cell. Several of the issues associated with the
construction of the vacuum vessel were control of dimensional
stability following welding and controlling the permeability of
the welds. A great deal of time and effort was devoted to
defining the correct weld process and material selection to
meet our design requirements.
The PFC's will be baked out at 350 degrees C while the vessel
is maintained at 150 degrees C. This required care in
designing the supports so they can accommodate the high
electromagnetic loads resulting from plasma disruptions and
the resulting relative thermal expansions between the PFC's
and the vacuum vessel on which supports are attached.
This paper will provide a brief review of the issues associated
with the design, fabrication and assembly of the NSTX Torus
system including those outlined above.
I. INTRODUCTION
NSTX achieved its first plasma in February 1999 and
began experimental operations in August 1999. Figure 1
shows the NSTX Test Cell towards the end of the assembly
phase. Princeton Plasma Physics Laboratory constructed
the device in collaboration with Oak Ridge Nationallaboratory, Columbia University, and the University of
Washington at Seattle.
Figure 1. .. .NSTX During Final Construction in
January 1999
HI. DESIGN OVERVIEW
A cross section of NSTX is shown in Figure 2. The
centerstack assembly in Figure 3 is the most complex and
critical component of NSTX. It was a modular design so
that it can be easily removed for future upgrades or
maintenance. The centerstack consists of the following
elements:
- Inner TF Leg Bundle is the innermost element of
the CS, consisting of (36) copper bars for the
central legs of the toroidal field (TF) system.
1. Surrounding the TF bundle is the Ohmic Heating
(OH) solenoid. The OH is wound on a 3mm
thick stainless steel tension tube that supports the
OH coil while permitting axial thermal expansion.
The 962 turn winding is arranged in 4 layers,
wound 2 in hand to provide 8 parallel cooling
paths in minimize thermal gradients (and shear
stresses) during cool down
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Neumeyer, C.; Barnes, G.; Chrzanowski, J.H.; Heitzenroeder, P. & al, et. National Spherical Torus Experiment (NSTX) Torus Design, Fabrication and Assembly, report, November 1, 1999; Princeton, New Jersey. (https://digital.library.unt.edu/ark:/67531/metadc625442/m1/1/: accessed April 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.