Structural Analysis at the Transition From W7-X Construction to Operation

IEEE Trans. Appl. Supercond.

et al. 2017

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The superconducting fusion device Wendelstein 7-X (W7-X) went into operation in December 2015. One of the most important steps was the commissioning of the superconducting magnet system. It consists of 70 superconducting coils, 14 HTS current leads, and more than 100 superconducting bus bars. The system is divided into seven electrical circuits with ten coils, associated bus bars and two current leads each. The commissioning of the magnet system was performed in two major steps: In a first step the seven coil circuits were separately energized and operated at several current levels in a range between 2 kA and 12.8 kA. In a second step all seven circuits were operated together. The adjustment of the quench detectors, the evaluation of the thermal and mechanical behavior, and the test of the magnet safety system were further work packages. Fast discharges were initiated to check the proper behavior of the magnet safety system. Steady-state operation of up to eight hours was performed to adjust the helium mass flows. The commissioning was successfully completed, the main goal of the magnet system is fully reached, which is also confirmed by magnetic flux measurements and the results of the first plasma operation.

Section: Findings and Results: Mechanical Behaviormentioning

confidence: 99%

Section: A Strategy and Organizationmentioning

confidence: 99%

Commissioning Results of the Superconducting Magnet System of Wendelstein 7-X

Rummel

Nagel

IEEE Trans. Appl. Supercond.

et al. 2017

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“…Due to MS complex structural design and a limited life time, each step of W7-X commissioning and operation is carefully monitored by a considerable amount of different sensors. Prior to the loading step a set of the boundary or limit values for MI signals are established to distinguish nominal, questionable, and critical state of the machine [10], [11], as also indicated in Fig. 3.…”

Section: B Monitoring Approachmentioning

confidence: 99%

Mechanical Monitoring Issues in Preparation to Next Step of Wendelstein 7-X Operation

IEEE Trans. Plasma Sci.

Carls

Zhu

et al. 2018

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The largest modular stellarator Wendelstein 7-X (W7-X) has successfully passed the first phase of operation in Greifswald, Germany. The sophisticated W7-X superconducting magnet system (MS) with its nonlinear support system has been carefully monitored using an extensive set of mechanical and temperature sensors. This paper focuses on detailed consideration of cyclic MS behavior during operation with limiter configurations of plasma. Measurement results are carefully compared with predictions from updated numerical models and critical issues are highlighted. As a result, the structural monitoring tool is extended to follow enhanced requirements and expectations. This paper is a preparation for upcoming more demanding phases with longer plasma pulses to guarantee safe and reliable W7-X operation with different divertor and scraper element configurations. The procedure to establish required sensor configurations, and to analyze and release new plasma regimes being compatible with W7-X component design values is also described. Index TermsNumerical finite-element (FE) analysis, stellarator, structural monitoring, Wendelstein 7-X (W7-X).

“…Main steps to achieve this goal have been formulated before commissioning and first phase of operation 5 : improvement of MI monitoring, benchmarking and update numerical modeling, neglecting unimportant features in FE models to accelerate the analysis. The strategy was successfully followed with the results described below in Chapter IV.…”

Section: Iia Strategymentioning

confidence: 99%

“…However, some average values strongly deviate from the results of FE predictions. 5 One of the possible reasons for the deviation might be the small SG extension with respect to the big grain size of the non-planar coil casing cast material. 11 Within a grain the material is anisotropic with stiffness ratios up to more than two between principle directions.…”

Section: Iiib Individual Tests Of Superconducting Coilsmentioning

confidence: 99%

Engineering Challenges of W7-X: Improvement of Numerical Modeling and Mechanical Monitoring After Commissioning and First Phase of Operation

Fusion Science and Technology

Zhu

Carls

et al. 2017

The largest modular stellarator Wendelstein 7-X (W7-X) has successfully passed commissioning and first phase of operation in Greifswald, Germany. The limiter configurations of plasma with 2.5 T of magnetic induction on the plasma axis produce already considerable loads (MN) in the W7-X systems. The sophisticated W7-X superconducting magnet system with its non-linear support system is instrumented with an extensive set of mechanical and temperature sensors. Measurement results showed that magnet system behavior is in good correspondence with original predictions from numerical models. However, several areas require modeling improvements and/or proper adjustment of parameters to reflect "as-built" situation. Moreover, high temperature dependence of strain gauge signal accuracy in the range below 10 K requires its compensation in order to avoid fault alarms during monitoring. The work is considered as benchmarking of numerical models and as a preparation for upcoming more demanding phases with longer plasma pulses to guarantee safe and reliable W7-X operation with different divertor configurations. Both results of W7-X measurements and implemented improvements as well as lessons learned so far are also given.