Abstract
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.
Highlights
AND MOTIVATIONThe largest modular stellarator Wendelstein 7-X (W7-X) has successfully passed commissioning and first phase of operation in Greifswald, Germany
The analysis reveals the importance of calibration, compensation, signal filtering, and careful signal synchronization
It is expected that much higher heat flux is to be delivered on the cryogenically cooled structures with corresponding increasing of temperature by few degree
Summary
The largest modular stellarator Wendelstein 7-X (W7-X) has successfully passed commissioning and first phase of operation in Greifswald, Germany. The high requirements regarding field symmetry and plasma study possibilities result in a sophisticated support system, tight tolerances, and advanced numerical modeling The latter is a demanding task due to the complex 3D configuration. The cryostat system is quite challenging from mechanical point of view considering the special geometry, different temperatures during operation and plasma vessel baking, as well as flexible and adjustable plasma vessel supports. In order to assess reliably the mechanical integrity of these systems during design, assembly, commissioning and operation, global finite element (FE) models in ANSYS and ABAQUS were created and intensely used for the benchmarking of FE results.. The large amount of non-linear components in the magnet system makes its behavior prediction challenging Another complication for the analysis of the MS is elements with different order of stiffness (e.g. coil cases and flexible tie-rods). In case of the experiment success, an optimized stellarator is to be considered as a mature option for the fusion reactor
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