Abstract
Cable-in-conduit conductors of the ITER magnet system are directly cooled by supercritical helium. Insulation breaks are required in the liquid helium feed pipes to isolate the high voltage system of the magnet windings from the electrically grounded helium coolant supply line. They are submitted to high voltages and significant internal helium pressure and will experience mechanical forces resulting from differential thermal contraction and electro-mechanical loads. Insulation breaks consist essentially of stainless steel tubes overwrapped by an outer glass – fiber reinforced composite and bonded to an inner composite tube at each end of the stainless steel fittings. For some types of insulator breaks Glass – Kapton – Glass insulation layers are interleaved in the outer composite. Following an extensive mechanical testing campaign at cryogenic temperature combined with leak tightness tests, the present paper investigates through non-destructive and destructive techniques the physical and microstructural characteristics of the low temperature high voltage insulation breaks and of their individual components, thus allowing to correlate the structure and properties of the constituents to their overall performance. For all the tests performed, consistent and reproducible results were obtained within the range of the strict acceptance criteria defined for safe operation of the insulation breaks.
Highlights
New generation superconducting magnets for fusion projects, such as ITER, widely use coils based on technology of Cable-In-Conduit Conductors (CICCs) [1]
Following an extensive mechanical testing campaign at cryogenic temperature combined with leak tightness tests, the present paper investigates through non-destructive and destructive techniques the physical and microstructural characteristics of the low temperature high voltage insulation breaks and of their individual components, allowing to correlate the structure and properties of the constituents to their overall performance
The Insulation Breaks (IBs) will be placed at the helium supply and return points of the different cryogenic circuits foreseen in the ITER magnet system
Summary
New generation superconducting magnets for fusion projects, such as ITER, widely use coils based on technology of Cable-In-Conduit Conductors (CICCs) [1]. CICCs are designed based on various types of stainless steel jackets, densely filled with Nb3Sn or NbTi superconducting strands, and subsequently compacted [2]. They are cooled by a forced flow of supercritical helium [3]. The magnet coils are directly connected to the helium supply pipes of the electrically grounded cryogenic distribution system. The IBs will be placed at the helium supply (inlets) and return points (outlets) of the different cryogenic circuits foreseen in the ITER magnet system.
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