Dynamic response analysis of superconducting coils in Wendelstein 7-X and mechanical quench test

Abstract

The Wendelstein 7-X (W7-X) modular stellarator is under construction at the Max-PlanckInstitut für Plasmaphysik in Greifswald, Germany. The W7 X magnet system contains 70 superconducting (sc) coils which are supported by a massive central steel ring structure via bolted connections and by numerous welded as well as gliding inter-coil elements. Load tests on prototypes of bolted coil to support ring connections whose flanges partially open during high field operation, and of sliding support structures between the coils showed that stick-slip events at their contact surfaces cause shock waves. In order to assess the risk of a shock-induced quench of the superconductor, one of the coils was subjected to impact loads -the so called mechanical quench (MQ) test -in the course of the cryogenic acceptance tests at CEA in Saclay, France. No quench could be triggered even with the lowest coil stability margin. The paper demonstrates that the amplitudes of the shock waves in the W7-X magnet system are comparable to those generated by the impacts in the MQ tests. For that purpose, finite element (FE) models of both W7-X and the MQ test simulating the dynamic responses were developed and successfully validated against measurements. The Wendelstein 7-X (W7-X) modular stellarator is under construction at the Max-Planck-Institut für Plasmaphysik in Greifswald, Germany. The W7-X magnet system contains 70 superconducting (sc) coils which are supported by a massive central steel ring structure via bolted connections and by numerous welded as well as gliding inter-coil elements.Load tests on prototypes of bolted coil to support ring connections whose flanges partially open during high field operation, and of sliding support structures between the coils showed that stick-slip events at their contact surfaces cause shock waves. In order to assess the risk of a shock-induced quench of the superconductor, one of the coils was subjected to impact loads -the so called mechanical quench (MQ) test -in the course of the cryogenic acceptance tests at CEA in Saclay, France. No quench could be triggered even with the lowest coil stability margin.The paper demonstrates that the amplitudes of the shock waves in the W7-X magnet system are comparable to those generated by the impacts in the MQ tests. For that purpose, finite element (FE) models of both W7-X and the MQ test simulating the dynamic responses were developed and successfully validated against measurements.

Specific Features of Wendelstein 7-X Structural Analyses

“…Worth to mention test programs supported by intensive structural analysis for highly loaded NSEs, CSEs, cryolegs, and conductor connections [23], as well as for the mechanical quench test on the superconducting NPC type 2 under current [24], [25]. Quality assurance for incoming material is also very important.…”

Structural analysis of W7-X: From design to assembly and operation

“…Worth to mention are particularly test programs supported by intensive structural analysis for highly loaded NSEs [13,14], CSEs [15], cryolegs [16] and conductor connections [17], as well as for the mechanical quench test on the superconducting NPC type 2 under current [27,28].…”

Structure Design and Analysis of Canted‐Cosine‐Theta (CCT) Superconducting Quadrupole Magnet

“…For higher efficiency, ten wires were placed in one groove by the 2 × 5 arrangement with series connection. e operating current is 400 A. e stability of superconducting magnet mechanical structure is one of the main reasons for quench [5][6][7][8], so the stress-strain analysis on the magnet structure plays an important role on the magnet design [9][10][11][12][13][14][15], particularly for the complex structure of the CCT quadrupole magnet. e analysis model is created by cutting a section from the structure with a pitch owing to its periodic symmetry in the axial direction.…”