NDTnet 1998 Aug, Vol.3 No.8

Full-Text - Abstract

Novel high-current superconducting cables have been developed for large scale magnets used in High Energy Physics and Superconducting Magnetic Energy Storage (SMES) systems. A superconducting flat-band-cable is coextruded with high-purity aluminium. Further mechanical reinforcement can be achieved by attaching high-strength aluminium alloy strips. For a satisfying service of the conductor a good bonding between the different constituents must be guaranteed. The main reasons are: cooling efficiency of the superconductor, current transfer to the high-purity aluminium in case of an emergency shut-down and mechanical stability. Modern ultrasonics is a well-known nondestructive technique to detect regions of disbanding. We have tested a large variety of aluminium stabilized superconducting cables in different development and production stages. Our laboratories are involved in projects in Europe (CMS, ATLAS), in USA (Fermilab DO, SMES, BABAR) and Janan (KEK).

Short samples (20 cm) are analysed with ultrasonic C-scan imaging applying the pulse-echo immersion technique. Focused ultrasonic probes with nominal frequencies up to 50 MHz are used in conjunction with a high-precision mechanical scanner.

For quality assurance reasons it is necessary to monitor the bond-quality continuously along the whole cable length (up to 80 km). Mechanical (x-y) scanning of the complete bond-area, however, takes up too much time. As a first step we performed a partial bond-test with two fixed 10 MHz point-focused probes. The echo amplitude of 1 mm bond-width was recorded in function of position. In this way we have continuously tested 5 km Fermilab DO cable on both sides. To control the quality of the whole bond-width over the total length we propose the phased array technique. The sound beam is scanned electronically perpendicular to the direction of production. That is why such a testing is sufficiently fast in order to allow a continuous analysis. A new 10 MHz linear array probe with 128 elements was designed and manufactured. With the new probe in conjunction with the appropriate electronics and software a large number of test samples were investigated.

In conclusion, we have demonstrated the power of ultrasonic imaging in the bond quality control of high-current superconducting cables. We are convinced that the continuous testing will be feasible with the phased array technique.

Fig. 10 MHz phased array C-scan of a Fermilab DO sample: disbonded areas are dark-grey (left and right)

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Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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