Quality Monitoring of the Electron Beam Welding of the CMS Conductor Using Ultrasonics

Abstract

CMS (Compact Muon Solenoid) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10,000-ton return yoke. Its magnet coil is wound from a pure aluminum stabilized superconductor. In order to withstand the considerable magnetic forces the conductor is reinforced by attaching high-strength aluminum alloy profiles using an Electron Beam (EB) welding process. 20 unit lengths of conductor, 2.5 km each, are needed. Only a complete bonding ensures the required mechanical strength of the conductor. The quality control of the welding is a key element in the success of the fabrication. Hence, we have introduced into the production line, just after the EB welding unit, a specifically developed ultrasonic imaging system. A high-speed phased-array instrument copes with the challenge of a continuous monitoring of the welding quality over the whole width and the complete length of the conductor. The performance of the ultrasonic inspection system and the assessment of ultrasonic indications with respect to different types of welding flaws is shown. By now over 45 km of the CMS conductor have been successfully welded and inspected.Index Terms-Bond quality, electron beam welding, nondestructive testing, ultrasonic phased-array technology.

Status of the Construction of the CMS Magnet

“…strand not to degrade it, the Rutherford cable has been limited to 32 strands, and thus the required current carrying capability of the strand has been pushed to the limit of what can be produced industrially, namely a of 3140 at 5 T and 4.2 K. Monitoring of conductor quality is of major importance for such a project. In particular, an ultrasonic scanning system has been developed at EMPA (Swiss Federal Laboratories for Materials Testing and Research, Dübendorf, Switzerland) to monitor the quality of the bonding during extrusion and the quality of the welds during the EB welding operation; complete results are reported in [6]. At the end of the manufacturing process, integral samples of conductor are measured (after removing the reinforcement) in the Marisa facility at Genova [7]; in addition, extracted strands are measured at Saclay.…”

Mechanical Properties of the CMS Conductor

“…The 20 kA superconductor consists of a superconducting Rutherford type cable stabilized with High Purity Aluminum (HPA), and mechanically reinforced with two continuous sections of aluminum alloy [3] welded by Electron Beam (EB) technology [4]. Continuous EB welding was developed to produce 2.6 km conductor unit lengths [5], with dedicated ultrasonic on-line quality monitoring [6]. The main characteristics of the conductor are summarized in Table I.…”