1. Max-Planck- Institut für Plasmaphysik Wendelstein 7-X An optimized stellarator Hans-Stephan Bosch Max-Planck Institute for Plasma Physics on behalf of the project team Wendelstein 7-X Graduiertenkolleg GRK1203 Düsseldorf-Jülich, Bad Breisig, October 27&28, 2008

2. Max-Planck- Institut für Plasmaphysik Outline of the talk I.Introduction stellarators, W7-X II.Island divertor experience from W7-AS III.Construction of W7-X overview and status IV.Concluding remarks

3. Max-Planck- Institut für Plasmaphysik 3 Reminder: the tokamak principle Tokamak (1951 Sacharov und Tamm) тороидальная камера в магнитных катушках „toroidal chamber in magnet coils“ radial shift of plasma axis j vf j tor induced toroidal plasma current ~ MAmps j tf toroidal magnetic field

4. Max-Planck- Institut für Plasmaphysik 4 Reminder: the stellarator principle Stellarator (1951 Spitzer) Stella = the star „bringing the star“ j hf helical magnetic field j tor  0 toroidal magnetic field j tf

5. Max-Planck- Institut für Plasmaphysik 5 Comparison Tokamak - Stellarator good neoclassical confinement toroidal symmetry  pulsed operation  current driven instabilities, disruptions  bad neoclassical confinement  no toroidal symmetry steady state operation no current driven instabilities current in coils and plasma current-carrying plasma self-organized equilibrium toroidal symmetry ~ 2d problem current in the coils only very small plasma current field-defined equilibrium no toroidal symmetry ~ 3d problem good neoclassical confinement  quasi-symmetry steadystate operation no current driven instabilities good neoclassical confinement toroidal symmetry  advanced scenarios ~ steady state  active control of plasma instabilities

6. Max-Planck- Institut für Plasmaphysik 6 The stellarator genealogy Stellarators C,Cleo,W7-A, L2, WEGA classical quasi-symmetric W7-AS advanced TorsatronsHeliotrons ATF, CAT, URAGAN He-E, LHD, He-J, CHS modular H1, TJ-II Heliacs HSX NCSX CHS-qa q-helicalq-axial q-poloid. W7-X QPS shut down operating under construction planned

7. Max-Planck- Institut für Plasmaphysik 7 Stellarator fields mod(B) classical quasi-helical quasi-poloidal quasi-toroidal quasi-isodynamic by courtesy of J. Sanchez

8. Max-Planck- Institut für Plasmaphysik 8 LHD R ax = 3.4 – 4.1 m, a ≤ 0.65 m V pl = 30m 3 B ≤ 2.9 T,  (0) ≥ 0.35,  (a) ≤ 1.5 high shear, 10 field periods, l = 2 W7-X R ax = 5.5 m, a ≤ 0.53 m V pl = 30m 3 B ≤ 3.0 T,  (0) ≥ 0.88,  (a) ≤ 0.97 low shear, 5 field periods Large Helical Device – Wendelstein 7-X PC coils HC coil LID coils

9. Max-Planck- Institut für Plasmaphysik 9 W7 vs. LHD magnetic configuration W7-AS |B| on flux surface R = 2 m W7-X |B| on flux surface R = 5.5 m LHD |B| on flux surface R = 3.6 m W7-line: avoid islands by low shear – LHD-heliotron: high shear, small islands

10. Max-Planck- Institut für Plasmaphysik 10 MHD equilibrium - comparison ≈ 4% ≈ 3% ≈ 2% LHD (HINT-Code) W7-X has the better high-pressure equilibrium stable edge for proper island divertor operation minimized island/stochastic layer formation W7-X (PIES-Code)

11. Max-Planck- Institut für Plasmaphysik 11 The optimized stellarator W7-X 1. feasible modular coils 2. good, nested magnetic surfaces 3. good finite-  equilibria 4. good MHD stability 5. small neoclassical transport 6. small bootstrap current 7. good confinement of fast particles 7 optimization criteria [Nührenberg] development tasks 1.optimum nT  E and high  discharges 2.steady state operation 3.plasma-wall interaction 4.island divertor operation 5.turbulent transport

12. Max-Planck- Institut für Plasmaphysik 12 Island divertor – the idea for comparison, poloidal divertor in a tokamak,ASDEX upgrade Island divertor in W7-X

13. Max-Planck- Institut für Plasmaphysik 13 The W7-AS island divertor one of five magnetic field periods schematic confinement region x-point island ergodic region 1 2534 key idea: natural islands are intersected with target separatrix elliptical plane

14. Max-Planck- Institut für Plasmaphysik 14 Operation without divertor – a problem no density control energy (radiation) collaps high z impurity accumulation radiation losses

15. Max-Planck- Institut für Plasmaphysik 15 Operation with divertor – HDH mode high density n e = 2.5  10 20 m -3 n e /n eGW = 2.5 high pressure  = 3.4%  N ~ 9.3 absorption P abs = 2.5 MW confinement H ISS95 = 1.4 MHD stability stationarity T flattop ~ 100  E

16. Max-Planck- Institut für Plasmaphysik 16 HDH - an advanced operation regime HDH-regime - a true bifurcation with hysteresis, profile differences,...  confinement of energy increases  confinement of impurities deteriorates the high-density high-confinement (HDH) mode discovered in 2002 on W7-AS

17. Max-Planck- Institut für Plasmaphysik 17 High-beta experiments in HDH- mode MHD modes dissappear at high  inwards shift of  =1/2 surface formation of magnetic well   3% [A. Weller] [A. Werner] (m,n)=(2,1)

18. Max-Planck- Institut für Plasmaphysik 18 W7-AS Performance /w island divertor Based on resonant magentic islands at the edge Probably the only divertor solution for stellarators Controlled heat and particle deposition Density control even at high plasma densities Establishment of High-density H-mode (HDH) - Established at n~1.5 … 2.5  10 20 m -3 - Quiescent and MHD stable  magnetic well formation - Different from ELM-free H-mode - Improved energy confinement - Impurity screening  high edge densities

19. Max-Planck- Institut für Plasmaphysik 19 Wendelstein 7-X main parameters key parameters major radius: 5.5 m minor radius: 0.53 m plasma volume30 m 3 non-planar coils:50 planar coils:20 number of ports:299 rot. transform:5/6 - 5/4 induction on axis:< 3T stored energy:600 MJ heating power15 - 30 MW pulse length: 30 min energy turn around:18 GJ machine height:4.5 m machine diameter:16 m machine mass:725 t cold mass:425 t

20. Max-Planck- Institut für Plasmaphysik 20 Project Control A. Lorenz Documentation U. Kamionka Power Supplies Th. Rummel Magnet Testing J. Baldzuhn Cryogenics M. Nagel Design Engineering V. Bykov Instrumentation J.P. Kallmeyer Development and Test D. Hathiramani On-Site Co-ordination S. Gojdka Device Assembly K.H Oelgemöller Cryostat T. Koppe Assembly Technology S. Jung Magnet Manufacturing K. Riße Project Coordination H.-S. Bosch (A. Lorenz) Magnets and Cryostat U. Nielsen (T. Rummel) Engineering F. Schauer (V. Bykov) Assembly L. Wegener (T. Bräuer) Physics R. Wolf/F. Wagner (R. König) In-Vessel Components F. Hurd (R. Stadler) Design Office D. Pilopp Configuration Control C. Baylard Configuration Management R. Brakel Design and Configuration D. Hartmann (R. Brakel) Diagnostics R. König High Frequency Heating V. Erckmann NBI A. Stäbler Periphery R. Krampitz Project W7-X T. Klinger R. Haange Divertor and First Wall R. Stadler CoDaC A. Werner Test-Divertor A. Peacock Wendelstein 7-X organisation strict procedures necessary e.g. quality management, change management 400 working directly on Wendelstein 7-X construction about 700.000h assembly time ahead ~ industrial workers Quality Management J.-H. Feist Coordination H.-S. Bosch Device Safety D. Naujoks

21. Max-Planck- Institut für Plasmaphysik 21 ports 50 non-planar coils 20 planar coils plasma vessel 10 half module cryostat 10 half shells central ring 10 segments thermal insulation components in plasma vessel bus bar system Wendelstein 7-X main components

22. Max-Planck- Institut für Plasmaphysik 22 Steady-state ECRH heating successful joint project high power gyrotrons 10  1MW 140GHz pulse length 30min quasi-optical beam duct world record shot 30min integrated cw design full system available 7/10 gytrotrons delivered

23. Max-Planck- Institut für Plasmaphysik 23 Steady-state divertor 1.target elements 10MW/m 2 CFC sealed on cooled CuCrZr 2.baffle elements 1MW/m2 graphite clamped on CuCrZr cryopumps control coils more than 1.000.000 pieces more than 100.000 pieces in the shop

24. Max-Planck- Institut für Plasmaphysik 24 Core component: superconducting coils drawing non-planar coil Coil status: 20 planar coils 50 non-planar coils 100M€ contract 100% manufactured 75% successfully cold tested

25. Max-Planck- Institut für Plasmaphysik 25 Paschen-testing of the coils  critical scenario: air influx into outer vessel causes pressure increase and quenching of a coil.  During a quench, high voltages arise – at increased pressure  Therefore all coils are tested under Paschen conditions (between 0.001 and 100 mbar) with 9 kV  This has also proven to be a good procedure to verify a good insulation.

26. Max-Planck- Institut für Plasmaphysik 26 Coil manufacturing completed

27. Max-Planck- Institut für Plasmaphysik 27 Coil tests under cryogenic conditions Thermal properties Cold leak tighness Helium flow rates Electrical insulation Superconductivity

28. Max-Planck- Institut für Plasmaphysik 28 plasma vessel modules thermal insulationouter vessel with domes Components and assembly central support ring modules

29. Max-Planck- Institut für Plasmaphysik 29 The outer vessel More than 500 openings ~ thermal insulation laborious

30. Max-Planck- Institut für Plasmaphysik 30 Threading of first non-planar coil 04/05

31. Max-Planck- Institut für Plasmaphysik 31 Coils threaded, Ass‘y of support structure 09/07

32. Max-Planck- Institut für Plasmaphysik 32 Transport of first half-module 02/08

33. Max-Planck- Institut für Plasmaphysik 33 2 Half-modules in ass‘y stand II 02/08

34. Max-Planck- Institut für Plasmaphysik 34 Bus-bar assembly in ass‘y stand II 07/08

35. Max-Planck- Institut für Plasmaphysik 35 Bus-bar assembly in ass‘y stand II 08/08

36. Max-Planck- Institut für Plasmaphysik 36 Assembly stand III 09/08

37. Max-Planck- Institut für Plasmaphysik 37 Schedule completion date 2014 68 weeks buffer time 29 milestones tight schedule control assembly in schedule

38. Max-Planck- Institut für Plasmaphysik 38 „Fully“ optimized magnetic field configuration with simultaneously … - low equilibrium currents - good magnetohydrodynamic equilibria - good magnetohydrodynamic stability - good neoclassical confinement - good fast-particle confinement First steady-state superconducting modular magnetic field coil system - steady-state island divertor for full power load - steady-state 10MW ECRH system with quasi-optical wave guide - steady-state consistent diagnostic and CoDac system Assembly complex and time-consuming, but it‘s on the way! A high-temperature plasma device for Europe and the world! Wendelstein 7-X stellarator features