Pressure-induced critical current reduction in impregnated Nb3Sn Rutherford cables for use in future accelerator magnets

P Gao,M Dhallé,H H J Ten Kate

doi:10.1088/1757-899x/756/1/012015

P Gao, M Dhallé + Show 1 more

Open Access

https://doi.org/10.1088/1757-899x/756/1/012015

Copy DOI

Abstract

The measured critical current reduction in Nb3Sn Rutherford cables under magnet-relevant transverse pressure levels is analyzed in terms of the strain state of the filaments inside their strands. Several straightforward mechanical 2D FE models of the cables’ cross-section are used to translate the stress that is applied to the surface of the impregnated cables into a strain distribution on its strands. The resulting critical current reduction of the cable is then estimated from the average deviatoric strain in the strands’ filamentary zone, using the well-established strain scaling relations obtained for isolated strands. This allows to identify the main factors that influence the pressure response of impregnated Nb3Sn accelerator cables. The analysis is presented for state-of-the-art cable samples that were measured at the University of Twente and shows how especially stiff and incompressible resins reduces the deviatoric strain in the filamentary zone of the cable strands, but also how relatively small alignment errors can lead to stress concentrations that reduce the critical current density significantly.

Highlights

In the frame of the ongoing development of the generation of particle colliders, CERN is designing multiple variants of Detector Magnets for the projected Physics Experiments at the Future Circular Collider (FCC), which includes electron-positron, electron-hadron and hadron-hadron collision detectors [1]
The Future Circular Collider (FCC) study includes the design of the detector magnets for the FCC-ee+ collider, requiring a 2 T solenoid for particle spectrometry, and for the FCC-hh collider, with a 4 T detector solenoid
The cryostats must be optimized to have maximum radiation transparency. They are structured as a sandwich of thinnest possible metallic shells for achieving vacuum tightness, supported by layers of low density and highly radiation transparent insulation material, still providing sufficient mechanical resistance and low thermal conductivity

Summary

Introduction

In the frame of the ongoing development of the generation of particle colliders, CERN is designing multiple variants of Detector Magnets for the projected Physics Experiments at the Future Circular Collider (FCC), which includes electron-positron (ee+), electron-hadron (eh) and hadron-hadron (hh) collision detectors [1]. CERN has investigated the compression of Cryogel® Z under 1 bar equivalent mechanical load and its thermal conductivity between 10 K and room temperature, as well as the critical phenomena of thermal shrinkage and outgassing. We present the results of the compression and thermal conductivity tests conducted on Cryogel® Z and the effects of possible thermal shrinkage and outgassing of the material.

Results

Conclusion