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Boyd Blackwell, H-1 National Facility Australian National University

Results from Helical Axis Stellarators. Thanks to: Enrique Ascasibar and TJ-II Group Prof. Obiki and Heliotron-J Group David Anderson and HSX Crew and the H-1 Team. Boyd Blackwell, H-1 National Facility Australian National University. Development of Helical Axis Stellarators.

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Boyd Blackwell, H-1 National Facility Australian National University

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  1. Results from Helical Axis Stellarators Thanks to:Enrique Ascasibar and TJ-II GroupProf. Obiki and Heliotron-J GroupDavid Anderson and HSX Crewand the H-1 Team Boyd Blackwell, H-1 National FacilityAustralian National University

  2. Development of Helical Axis Stellarators Spitzer 1951 - figure-8 stellarator  “spatial axis” which produces rotational transform magnetic hill  unstable to interchange Koenig 1955 - helical winding/axis:  = 1  single pair of helices Spitzer 1956  possibility of shear stabilization for higher order windings  = 2,3demonstrated theoretically (resistivity  0) Johnson et al 1958 Furth, Killeen, Rosenbluth 1963found resistive interchange instability possible even at low resistivity for small scale lengths 1964-5 several configurations proposed with magnetic well (average minimum B) found including heliac (straight). Exploitation of avg. min B  regions of bad curvature  possible ballooning instability -I +I  = 1 

  3. Development of Helical Axis Stellarators II Nagao 1977Asperator NP: toroidal helical axis stellarator (+extra helical windings) Yoshikawa... 1982-4 - toroidal heliac HX-1 proposal Blackwell, Hamberger... 1984 - SHEILA prototype heliac (0.2M, 0.2T, 1019m3) 1985 - Tohoku, H-1 and TJ-II and heliacs proposed - and HBTX linear heliac UW - Operation in 1987 (Tohoku, Sendai) 1992 (H-1) and 1996(TJ-II, Spain) 1988 Nuhrenberg and Zille - quasi-helical symmetry - restore outstanding features of straight heliac. [transport, beta limit(Monticello et. al 1983)] 1996-9Heliotron-J - combine heliotron/torsatron with advances in transport (optimise bumpy cpt, quasi-isodynamic) 1999 Helically SymmetricEXperiment first quasi-symmetric experiment exploit high iota, N-m scaling

  4. Helical Axis Stellarators 2000 Canberra, Australia external vacuum vessel CIEMAT, Madrid internal vessel, upgrade to NBI IAE Kyoto “inverted heliac” bumpy field cpt TSL, Madisoncontrolled “spoiling” of symmetry . Device Type Aspect Iota H-1 Heliac3 period heliac, toroidal>helical 5  0.6-1.9 TJ-II Heliac4 period heliac, helical>toroidal 7  0.9-2.2 Heliotron Jhelical axis heliotron (TFC + =1) 7-11 0.2-0.8 HSXmodular coils, helical symmetry 8 1.05-1.2

  5. Summary - Future • Confinement in heliacs ~ISS95 or better (2keV, ~5ms). Ion beam probe to elucidate role of Eradial in improved confinement • New configurations with improved neoclassical transport initial results promising, await full analysis • HSX/H-J can compare similar configurations with vastly different neoclassical transport predictions . • Confinement transitions possible at low power, many similarities with large devices/powers. Investigate effect of E-field imposed by localised ECH. • No serious impurity accumulation problems yet. Real test when the ions are strongly heated • No fatal instabilities observed yet. Several devices should have the heating capacity to test ballooning limits, at least in degraded configurations (consequence of flexibility).

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