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B. Stratton 10-23-03

W-7X, W7-AS, and diagnostics highlights from the 14 th International Stellarator Workshop Sept. 22-26, Greifswald, Germany. B. Stratton 10-23-03. W7-X Construction Status (J.-H. Feist and W7-X Construction Team). First plasma delayed until 2009-2010

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B. Stratton 10-23-03

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  1. W-7X, W7-AS, and diagnostics highlights from the 14th International Stellarator WorkshopSept. 22-26, Greifswald, Germany B. Stratton 10-23-03

  2. W7-X Construction Status(J.-H. Feist and W7-X Construction Team) • First plasma delayed until 2009-2010 • Due to delay in superconductor delivery and longer time foreseen for machine assembly • Modular coil construction now well advanced • 2 complete coils in casings delivered, 1 more ready for delivery, many others in progress • 1 coil cooled and successfully tested under power at Saclay • Planar coils >3 years behind schedule • 1st coil to be delivered in Oct., require 1-2 per month from now on • Other systems (vacuum vessel, ECRH, NBI, cryogenics, power supplies, etc.) making good progress and not on critical path • We got a lengthy tour-very impressive facility

  3. Max-Planck-Institut für Plasmaphysik Schematic View of W7-X Main Parameters: Major radius: 5.5 m Minor radius: 0.53 m Plasma volume 30 m3 Non-planar coils: 50 Planar coils: 20 Rotational transform: 5/6 - 5/4 Induction on axis: 2.5 T (< 3T) Stored energy: 600 MJ Heating power 15 - 30 MW Nominal pulse length: 30 min Machine height: 4.5 m Machine diameter: 16 m Machine mass: 725 t Cold mass: 425 t (J.-H. Feist)

  4. Max-Planck-Institut für Plasmaphysik Magnet system - Superconductor Strand Filaments CICC Superconductor NbTi Copper/Superconductor 2.5 - 2.9 Strand Diameter 0.58 mm Number of Strands243 Jacket Material AlMgSi Outer Dimensions16x16 mm2 Wall Thickness > 2mm Void Fraction37 % ± 2% Critical Current (4.2 K, 6T) > 36 kA Status of superconductor - Stringent quality control necessary - Start of series production delayed by 2 years - 75 % of conductor is produced (> 40 km) - 55 % at manufacturer´s premises Double layer length at Europa Metalli (J.-H. Feist)

  5. Max-Planck-Institut für Plasmaphysik Magnet system - Winding packages • Status of winding packages • Five winding lines fully operational • Winding forms with high accuracy • Shape reproducible within < 3 mm • 12 winding packages completed • 10 winding packages under work • Production time 38 -> 18 weeks Low resistance joints - 1 n See Riße, P.Mo20 (J.-H. Feist)

  6. W7-AS(R. Jaenicke and K. McCormick) • Operation ended July 31, 2002 after 14 years of operation • Many results: • Pressure-driven currents minimized • High b operation with good MHD stability • Optimization to reduce trapped particle fraction successful • High confinement regimes: Elmy H-mode, HDH mode • Island divertor successful • HDH mode found during operation with island divertor: • Makes possible long pulse operation at high density and high heating power. • High confinement: tE~2 X tEISS95 • Not understood

  7. Good MHD Stability Required high-b stability at Bo = 0.8 T on W7-AS - b  3.4 %/ b(0)  7 % obtained - MHD-activity mainly in medium-b phase, almost quiescent high-b phase  still no high-b limit perceptible sX-ray Tomographie  ballooning type perturbation (R. Jaenicke) 10

  8. (K. McCormick)

  9. (K. McCormick)

  10. (K. McCormick)

  11. (K. McCormick)

  12. Density Limit on W7-AS determined by radiative collapse only Hugill-diagram for W7-AS high-b discharges (A. Weller) in detached HDH- mode: up to 4 x 1020 [m-3] comparison with tokamak results not straightforward, essential message: - much higher densities accessible on W7-AS than in tokamaks - no Greenwald limit ? = ? no limit by instabilities (compare stability of high-b discharges) - instead: density limit determined by excessive impurity radiation (R. Jaenicke) 13

  13. Diagnostics • Use of MOSS spectroscopy to image Ti and flows in H-1 Heliac (J. Howard, Australian Nat. Univ.) • Modulated Optical Solid State interferometry • Possible application to CHERS, MSE, and Thomson Scattering • Interest in collaboration between W7-X diagnostics group and NCSX (Hartfuss) • Will discuss at HTPD Conference in April 2004 • Possible loan of diagnostics hardware (W7-X or W7-AS) to NCSX? • Interest in diagnostics collaborations between TJ-II and NCSX (Sanchez)

  14. Imaging systems allow detailed force balance studies Electron density Ion temperature Spontaneous transition Flow speed Brightness (J. Howard) Gas: argon BField: 0.06T rf: 7MHz 80kW pressure: 25mT

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