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(IC/P-05) Physics Issues for a Very-Low-Aspect-Ratio Quasi-Poloidal Stellarator (QPS)

J.F. Lyon1), L.A. Berry1), S.P. Hirshman1), D.A. Spong1), D.J. Strickler1), P.K. Mioduszewski1), B.E. Nelson1), D.E. Williamson1), A.S. Ware2), E. Barcikowski2), A.J. Deisher2), A. Brooks3), G.Y. Fu3), D. Mikkelsen3), D.A. Monticello3), N. Pomphrey3), R. Sanchez4)
1) Oak Ridge National Laboratory, Oak Ridge, TN, USA
2) University of Montana-Missoula, Missoula, Montana, USA
3) Princeton Plasma Physics Laboratory, Princeton, NJ, USA
4) Universidad Carlos III de Madrid, Madrid, Spain

Abstract.  A quasi-poloidal stellarator with very low plasma aspect ratio (R/a $ \sim$ 2.7, 1/2-1/4 that of existing stellarators) is a new confinement approach that could ultimately lead to a high-beta compact stellarator reactor. The Quasi-Poloidal Stellarator (QPS) experiment is being developed to test key features of this approach. The QPS will study neoclassical and anomalous transport, stability limits at beta up to 2.5%, the configuration dependence of the bootstrap current, and equilibrium robustness. The quasi-poloidal symmetry leads to neoclassical transport that is much smaller than the anomalous transport. The reduced effective field ripple may also produce reduced poloidal viscosity, enhancing the ambipolar E x B poloidal drift and allowing larger poloidal flows for reduction of anomalous transport. A region of second stability exists in QPS at higher beta. Very-high-beta configurations with a tokamak-like transform profile have also been obtained with a bootstrap current 1/3-1/5 that in an equivalent tokamak. These configurations are stable to low-n ideal MHD kink and vertical instabilities for beta up to 11%. Ballooning-stable configurations are found for beta in the range 2% to 23%.

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IAEA 2003