Proceedings of ITC/ISHW2007

Status of the QPS Project
J. F. Lyon, B. E. Nelson, J. H. Harris, D. A. Spong, R. D. Bensona, M. J. Cole, P. J. Fogartyb,
K. D. Freudenberg, P. Goransonb, A. Lumsdainea, M. Madhukara, T. E. Shannona,
G. H. Neilsonc, P. Heitzenroederc
aOak Ridge National Lab., Fusion Energy Division, Oak Ridge, TN, USA
The University of Tennessee, Magnet Development Laboratory, Knoxville, TN, USAb
DevTech, Clinton TN, USAcPrinceton Plasma Physics Laboratory, Princeton NJ, USAlyonjf@ornl.gov

The Quasi-Poloidal Stellarator (QPS) is being developed to test key stellarator physics issues
at plasma aspect ratios 1/2-1/4 that of other stellarators. QPS has a quasi-poloidal(linked-mirror-like) rather than quasi-toroidal (tokamak-like) magnetic configuration, whichallows poloidal flow and poloidal flow shear a factor of ~10 larger than in any other toroidal
confinement system, and very low effective ripple to reduce neoclassical transport. It is the
only toroidal device stable to drift wave turbulence over a range of temperature and density
gradients, which should reduce anomalous transport even in absence of flow shearing. The
magnetic field structure leads to a large fraction of trapped particles in regions oflow/favorable field line curvature, which strongly reduces the drive for a class oftrapped-particle instabilities. All other toroidal devices have a significant fraction of thetrapped particles in regions with bad curvature. QPS also allows extending the stellarator database to very low aspect ratio (R/a > 2.3), similar to the ST extending the tokamak data base tovery low R/a.
The complex 3-D design requirements (large plasma radius at very low aspect ratio, a plasma
cross section that varies toroidally from bean-shaped to D-shaped, and five types of
toroidally-elongated non-planar coils) and the need for reduced cost and risk in fabrication
drive the design. There are 2 field periods with 10 coils per period, 3 sets of poloidal fieldcoils and 12 toroidal field coils. Independent controls on these coil currents permit varying
key physics features by factor 10–30: the degree of quasi-poloidal symmetry, poloidal flow
damping, neoclassical transport, stellarator/tokamak shear and trapped particle fraction.
The QPS design consists of complex, highly accurate, stainless steel modular coil winding
forms that are cast and machined; conductor wound directly onto the winding forms; avacuum-tight cover welded over each coil pack; coils vacuum pressure impregnated; and thewinding forms bolted together to form a structural shell inside the vacuum vessel. The largest
and most complex of the winding forms has been cast using a patternless process and is being
precision machined. An internally cooled, compacted cable conductor that can be wound into
complex 3-D shapes has been developed. High-temperature cyanate ester resin is used for
vacuum pressure impregnation of the coils because it has several important advantages overthe usual epoxy, including higher operating temperature, lower water absorption, and better
handling characteristics during vacuum impregnation. Winding clamps were designed andfabricated with an open design that allows conductors to be placed and positioned in both thelateral and vertical directions automatically, without the need for additional geometricmeasurements or calibrated clamping pressure.