Advancement of Nb3Sn quadrupoles in the HL-LHC project

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概要

About one hundred magnets of six different types shall be installed in the High Luminosity LHC (HL-LHC) in the years 2026-2028 at CERN. These accelerator magnets are characterized by (i) a large aperture (105 to 150 mm) inducing large accumulation of stress due to electromagnetic forces, (ii) tight requirements on field quality due to the large values of the particle amplitudes in this region, and (iii) small series (6 to 20 magnets of the same type) giving a limited possibility of feedback and tuning during production. The magnet design, construction and test are based on CERN collaborations with institutes and industrial partners in USA, Spain, Italy, Japan and China.
The most challenging magnet, the Nb3Sn quadrupoles have a conductor peak field in operational conditions above 11 T, and an unprecedented length of 4.2 m (Q1 and Q3, manufactured and tested in the US) and 7.15 m (manufactured and tested at CERN). In this talk we will present the main results of the quadrupole program, including the short model program and the full-length prototypes. We will focus on the main achievements and challenges in terms of quench performance, endurance tests, field quality and protection. Finally, we will discuss the critical issues found so far in terms of performance, and the sophisticated tools used to address them.

Todesco氏は、CERN HL-LHCアップグレードで刷新される超伝導磁石群の責任者です。
今回のセミナーでは、ビーム衝突ルミノシティー増強の鍵を握る、ビーム最終収束用Nb3Sn超伝導四極磁石の進展について講演していただきます。
HL-LHCでは加速器用超伝導磁石として初めてNb3Sn超伝導線材を採用することで、磁石の高磁場化を実現します。
しかし、化合物であるNb3Snは機械的に非常に脆いため、高磁場＝高応力の状態下で安定して性能を発揮できる磁石を開発することは単純ではありませんでした。
今回の講演では、長年にわたる磁石開発で得られた重要な知見や課題を克服するための様々な工夫について、ご報告いただきます。