Submitted by szolling on

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Abstract:

A 100 TeV scale Hadron Collider is being considered for the post-LHC era. The expected nominal operation field of 15-16 T requires using magnets at the limit of Nb3Sn technology. Practical demonstration of this field level in an accelerator-quality magnet is a key condition to realize such a machine. In 2015 Fermilab has started the development of a Nb3Sn dipole demonstrator for a 100 TeV scale collider. Since 2016 it became a key task of the newly established U.S. Magnet Development Program. The main challenges for 15-16 T Nb3Sn magnets include large multilayer coil, strong mechanical structure to intercept Lorentz forces, and large stored energy. The strong forces generate high stresses in the coil and mechanical structure and, thus, require stress control to maintain them below 150 MPa, which is considered acceptable for brittle Nb3Sn. The large stored energy leads to further complications in the magnet quench protection.

The design of the Nb3Sn Dipole Demonstrator developed at Fermilab is based on 60-mm aperture 4-layer shell-type coils, graded between the inner and outer layers to maximize the magnet performance, and cold iron yoke. The cable in the two innermost layers has 28 strands 1.0 mm in diameter and the cable in the two outermost layers has 40 strands 0.7 mm in diameter. Both cables have been developed and fabricated at Fermilab in long lengths using RRP Nb3Sn wires produced by Bruker-OST. An innovative mechanical structure based on aluminum I-clamps and a thick stainless-steel skin was developed to preload brittle Nb3Sn coils and support large transverse and axial Lorentz forces. Analysis has shown that with conductor limit close to 17 T at 1.9 K the maximum field for this design is limited by 15 T due to mechanical considerations.

In June 2019 Fermilab has assembled and tested the 1-m long model of the Nb3Sn dipole demonstrator named MDPCT1, which produced a world record field of 14.1 T at 4.5 K. The first magnet assembly was done with lower coil pre-load to achieve 14 T and minimize the risk of coil damage during assembly. Next the magnet was reassembled with nominal pre-load to achieve its design field limit. In the second test the magnet reached 14.5-14.6 T bore field at 1.9 K and then showed large degradation of its quench performance. After tests the magnet was disassembled to the level of individual coils, and all the key structural components and the coils were inspected, and results were analyzed. In this talk I will present the details of MDPCT1 dipole design and its fabrication, discuss the magnet test results and lessons learned, and outline the next steps towards the limit of Nb3Sn high-field accelerator magnet technology.

Type
Meeting
Timezone
Europe/Zurich
Room
ZOOM
Category
MSC Seminars
Category ID
2265
Indico iCal
https://indico.cern.ch/export/event/1145779.ics
Room Map URL
https://cern.zoom.us/j/94326148529?pwd=azRpMFlYZ0EzdHpUR3JtSmJLZkVidz09
Start Date
End Date