Minimum quench power dissipation and current non-uniformity in ITER type NbTi cable-in-conduit conductor samples under DC conditions

TL;DR

This study analyzes current non-uniformity and quench power dissipation in ITER NbTi cable-in-conduit conductors under DC conditions using detailed numerical modeling, highlighting factors affecting quench stability and hot spot formation.

Contribution

The paper introduces a comprehensive numerical model that accurately predicts strand power distribution and hot spots in ITER-type conductors, considering detailed cable and magnetic field configurations.

Findings

The model accurately predicts transport properties of CICC samples.

Local thermal effects are marginal compared to temperature margins.

Hot spots can be identified based on current and magnetic field distribution.

Abstract

The level of current non-uniformity in NbTi CICCs sections near the joints in combination with the magnet field profile needs attention in view of proper joint design. The strand Joule power and current distribution at quench under DC conditions of two samples of ITER Poloidal Field Coil conductors, as tested in the SULTAN facility and of the so called PFCI Model Coil Insert, have been analyzed with the numerical cable model JackPot. The precise trajectories of all individual strands, joint design, cabling configuration, spatial distribution of the magnetic field, sample geometry and using experimentally determined interstrand resistance distributions have been taken into account. Although unable to predict the quench point due to the lack of a thermal-hydraulic routine, the model allows to assess the instantaneous strand power at quench and its local distribution in the cable, showing the hot spots, once the quench conditions in terms of current and temperature are experimentally known., The analysis points out the relation of the above mentioned factors with the DC quench stability of both short samples and coils. The possible small scale and local electrical-thermal interactions were ignored in order to examine the relevance of such effects in the overall prediction of the CICC performance The electromagnetic code shows an excellent quantitative predictive potential for CICC transport properties, excluding any freedom for matching the results. The influence of the local thermal effects in the modeling is identified as being marginal and far less than the generally accepted temperature margin for safe operation.