W-7X, W7-AS, and diagnostics highlights from the 14th 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– 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

Schematic View of W7-X Max-Planck-Institut für Plasmaphysik

Main Parameters:Major radius: 5.5 mMinor radius: 0.53 mPlasma volume 30 m3

Non-planar coils: 50Planar coils: 20Rotational transform: 5/6 - 5/4Induction on axis: 2.5 T (< 3T)Stored energy: 600 MJHeating power 15 - 30 MWNominal pulse length: 30 min

Machine height: 4.5 mMachine diameter: 16 mMachine mass: 725 tCold mass: 425 t

(J.-H. Feist)

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Magnet system - Superconductor Max-Planck-Institut für Plasmaphysik

Superconductor NbTiCopper/Superconductor 2.5 - 2.9Strand Diameter 0.58 mmNumber of Strands 243Jacket Material AlMgSiOuter Dimensions 16x16 mm2

Wall Thickness > 2mmVoid Fraction 37 % ± 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

CICCStrand Filaments

Double layer length at Europa Metalli

(J.-H. Feist)

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Magnet system - Winding packages Max-Planck-Institut für Plasmaphysik

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

See Riße, P.Mo20

Low resistancejoints - 1 n

(J.-H. Feist)

W7-AS(R. Jaenicke and K. McCormick)

• Operation ended July 31, 2002 after 14 years of operation• Many results:

– Pressure-driven currents minimized– High 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: E~2 X EISS95

• Not understood

high- stability at Bo = 0.8 T on W7-AS Good MHD Stability Required

sX-ray Tomographie ballooning type perturbation

- 3.4 %/ (0) 7 % obtained- MHD-activity mainly in medium- phase, almost quiescent high- phase

still no high- limit perceptible

10(R. Jaenicke)

(K. McCormick)

(K. McCormick)

determined by radiative collapse onlyDensity Limit on W7-AS

in detached HDH- mode:up to 4 x 1020 [m-3]

comparison with tokamak resultsnot straightforward, essential message:- much higher densities accessible on W7-AS than in tokamaks- no Greenwald limit ? = ? no limit by instabilities (compare stability of high- discharges)- instead: density limit determined by excessive impurity radiation

Hugill-diagram for W7-AS high- discharges (A. Weller)

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(R. Jaenicke)

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)

Imaging systems allow detailed force balance studies

Electron density Ion temperature

Brightness Flow speedSpontaneous transition

Gas: argon BField: 0.06T rf: 7MHz 80kW pressure: 25mT

(J. Howard)