Experiences from design and production of Wendelstein 7-X magnets
01 Jun 2009-Vol. 84, Iss: 7, pp 1619-1622
TL;DR: The Max-Planck-Institut fur Plasmaphysik in Greifswald is building the stellarator fusion experiment Wendelstein 7-X and the coils are passing the acceptance tests at cryogenic temperatures at CEA Saclay with a very good performance.
Abstract: The Max-Planck-Institut fur Plasmaphysik in Greifswald is building the stellarator fusion experiment Wendelstein 7-X (W7-X). The manufacturing of the W7-X superconducting magnet system, which consists of 50 non-planar and 20 planar coils, was finished in March 2008. The production was a technical challenge for the W7-X design crew as well for the manufacturer due to the complex 3 D shape of the non-planar coils and the stringent requirements for geometrical tolerances. The manufacturers had to solve several technical problems and to consider major design changes even at advanced stages of manufacture. Finally the coils are passing the acceptance tests at cryogenic temperatures at CEA Saclay with a very good performance. Results of the W7-X coil production will be given and critical production steps will be identified. Lessons will be taken from the experiences gained from design, manufacturing and test methods. The reasons for the considerable time delays will be explained.
Citations
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01 Jun 2009
TL;DR: Wendelstein 7-X (W7-X) as mentioned in this paper is the continuation of fusion experiments of the stellarator type at the Max-Planck Institute for Plasma Physics (IPP).
Abstract: Wendelstein 7-X (W7-X) represents the continuation of fusion experiments of the stellarator type at the Max-Planck Institute for Plasma Physics (IPP). The aim of W7-X is to demonstrate the suitability for a fusion reactor of this alternative type of magnetically confined plasma experiment. W7-X is being built at Greifswald in the northeast of Germany. The size of device (725 tons, height of 5 m, diameter 16 m) and the superconductive magnet system distinguish W7-X from earlier stellarators at IPP. The paper provides a summary of the status of the main components, the mastering of the technical challenges during component acceptance testing and during machine assembly. Latest results of the assembly work are especially highlighted. The scope of the construction of W7-X was modified and additional acceleration measures were implemented to mitigate risks and delays. Some aspects of these changes are explained in this paper.
63 citations
TL;DR: In this paper, a method to design coils for stellarators is presented, where each discrete coil is represented as an arbitrary, closed, one-dimensional curve embedded in three-dimensional space.
Abstract: Finding an easy-to-build coils set has been a critical issue for stellarator design for decades. Conventional approaches assume a toroidal 'winding' surface, but a poorly chosen winding surface can unnecessarily constrain the coil optimization algorithm, This article presents a new method to design coils for stellarators. Each discrete coil is represented as an arbitrary, closed, one-dimensional curve embedded in three-dimensional space. A target function to be minimized that includes both physical requirements and engineering constraints is constructed. The derivatives of the target function with respect to the parameters describing the coil geometries and currents are calculated analytically. A numerical code, named flexible optimized coils using space curves (FOCUS), has been developed. Applications to a simple stellarator configuration, W7-X and LHD vacuum fields are presented.
47 citations
TL;DR: In this paper, the 4C thermal-hydraulic code is validated against experimental data from the cooldown of a non-planar coil of the Wendelstein 7-X stellarator from room temperature to the superconducting transition temperature of ∼10 K, performed during the cold test of the full set of coils at the cryomagnetic test facility of CEA Saclay.
27 citations
TL;DR: In this article, the authors investigate if the existence of a toroidal "winding" surface unnecessarily constrains the optimization, and a new method to design coils for stellarators is presented.
Abstract: Finding an easy-to-build coils set has been a critical issue for stellarator design for decades. Conventional approaches assume a toroidal "winding" surface. We'll investigate if the existence of winding surface unnecessarily constrains the optimization, and a new method to design coils for stellarators is presented. Each discrete coil is represented as an arbitrary, closed, one-dimensional curve embedded in three-dimensional space. A target function to be minimized that covers both physical requirements and engineering constraints is constructed. The derivatives of the target function are calculated analytically. A numerical code, named FOCUS, has been developed. Applications to a simple configuration, the W7-X, and LHD plasmas are presented.
22 citations
TL;DR: In this article, a method for designing coils with finite builds and a mechanism to optimize the orientation of the winding pack is presented, which can approximate finite-build coils with a multi-filament model.
Abstract: Finding coil sets with desirable physics and engineering properties is a crucial step in the design of modern stellarator devices. Existing stellarator coil optimization codes ultimately produce zero-thickness filament coils. However, stellarator coils have finite depth and thickness, which can make the single-filament model a poor approximation, particularly when coil build dimensions are relatively large compared to the coil–plasma distance. In this paper, we present a new method for designing coils with finite builds and present a mechanism to optimize the orientation of the winding pack. We approximate finite-build coils with a multi-filament model. A numerical implementation has been developed, and applications to the Helically Symmetric eXperiment stellarator and a new UW-Madison quasihelically symmetric configuration are shown.
14 citations
References
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01 Jun 2009
TL;DR: Wendelstein 7-X (W7-X) as mentioned in this paper is the continuation of fusion experiments of the stellarator type at the Max-Planck Institute for Plasma Physics (IPP).
Abstract: Wendelstein 7-X (W7-X) represents the continuation of fusion experiments of the stellarator type at the Max-Planck Institute for Plasma Physics (IPP). The aim of W7-X is to demonstrate the suitability for a fusion reactor of this alternative type of magnetically confined plasma experiment. W7-X is being built at Greifswald in the northeast of Germany. The size of device (725 tons, height of 5 m, diameter 16 m) and the superconductive magnet system distinguish W7-X from earlier stellarators at IPP. The paper provides a summary of the status of the main components, the mastering of the technical challenges during component acceptance testing and during machine assembly. Latest results of the assembly work are especially highlighted. The scope of the construction of W7-X was modified and additional acceleration measures were implemented to mitigate risks and delays. Some aspects of these changes are explained in this paper.
63 citations
"Experiences from design and product..." refers background in this paper
...Planck-Institut für Plasmaphysik (IPP) in Greifswald Germany, see figure 1 [1]....
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TL;DR: In this article, the authors reviewed three decades of conductor R&D, prototypes, model coils and actual fusion devices with special attention to the drivers of the design of the conductor options.
Abstract: Three decades of conductor R&D, prototypes, model coils and actual fusion devices are reviewed with special attention to the drivers of the design. The conductor options are affected by the requirements typical of the fusion devices (large size and stored energy, high field, heat removal rate). The mechanical loads, operating voltage, ac loss and stability further restrict the freedom of the designer. On the other hand, the evolution of the available technologies for cryogenics and superconducting materials opens new frontiers for performance, reliability and cost. The lessons learned from the a dozen superconducting fusion devices are highlighted, starting from T-7, through MFTF, T-15, TRIAM, Tore Supra, LHD till the newest projects in construction, W-7X, EAST, SST-1, KSTAR. Some discussion is also devoted to the lessons that we keep refusing to learn
36 citations
TL;DR: In this article, an analytical procedure was developed to model both the current distribution in a cable consisting of many superconducting strands with resistive electrical contact between them and non-uniform contacts to the current supply at the ends.
29 citations
"Experiences from design and product..." refers background in this paper
...The premature quenches can be explained by the inhomogeneous current distribution caused by different strand contact resistances inside the joints [4], the relative short length of the...
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...test sample which did not allow an even current distribution between the strands in the cable [4] and a local superposition of the background field with the self field of the conductor on the high...
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01 Jun 2006
TL;DR: In this paper, a cable-in-conduit (CIC) conductor of 243 NbTi strands was used for the W7-X Stellarator, which can resist the large magnetic forces acting during magnet operation.
Abstract: The magnet system of the W7-X Stellarator consists of 50 non-planar and 20 planar coils. The superconductors for both types have the same design, which is a Cable-in-Conduit (CIC) conductor of 243 NbTi strands. Namely the non-planar coils asked for a conductor, which can be easily wound to a complex shape, but has high mechanical strength to resist the large magnetic forces acting during magnet operation. This has been achieved by jacketing the cable into an Aluminium conduit by a co-extrusion process. The used 6063 Aluminium alloy is very soft in the extruded state, but gets high strength properties after winding during a precipitation hardening treatment at about 160°C. The production of the needed 390 conductor lengths (including spares) and the related QA tests are nearly completed and a large number of coils are fabricated. Some of them were already subjected to a cold test at CEA Saclay, where the conductor behaved as expected from short sample measurements.
16 citations
"Experiences from design and product..." refers background or result in this paper
...were extrapolated to higher temperatures [2] in comparison to the line of the CRPP Ic test data [2, 3]....
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...Due to the triangular shape of the subcables the chosen cabling law leads to deep grooves between the sub-cables, which cannot be avoided [3]....
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TL;DR: It is concluded that combined high- voltage ac and low-voltage impedance spectrum tests are ideal means to rule out short circuits in the W7-X coils.
Abstract: The impedance spectrum test was employed for detection of short circuits within Wendelstein 7-X (W7-X) superconducting magnetic field coils. This test is based on measuring the complex impedance over several decades of frequency. The results are compared to predictions of appropriate electrical equivalent circuits of coils in different production states or during cold test. When the equivalent circuit is not too complicated the impedance can be represented by an analytic function. A more detailed analysis is performed with a network simulation code. The overall agreement of measured and calculated or simulated spectra is good. Two types of short circuits which appeared are presented and analyzed. The detection limit of the method is discussed. It is concluded that combined high-voltage ac and low-voltage impedance spectrum tests are ideal means to rule out short circuits in the W7-X coils.
11 citations
"Experiences from design and product..." refers background in this paper
...determine short circuits than the ohmic measurements or the AC tests [9]....
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