Critical Current Measurements of High-&lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$J_{c}$&lt;/tex&gt; &lt;/formula&gt; &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$\hbox{Nb}_{3}\hbox{Sn}$&lt;/tex&gt;&lt;/formula&gt; Rutherford Cables Under Transverse Compression

High-performance Nb 3 Sn superconducting wires have become one of the key technologies for the development of next generation accelerator magnets. While their large critical current densities enable the design of compact accelerator-quality magnets for their operation above 10 T, the noticeable reduction of the conductor performance due to mechanical strain appears as a new essential characteristic in magnet design.In this work, we extensively investigate the effect of transverse loads, up to 250 MPa, in state-of-the-art Nb 3 Sn Restacked-Rod-Process round superconducting wires. The tests are performed using a compressive Walters spring device, where the force is applied to the resin-impregnated wire, and the critical current is measured under magnetic fields ranging from 16 to 19 T. As a complement, critical current measurements under axial strain are also performed using a standard Walters spring. Interestingly, the study shows that the wire's electro-mechanical response under transverse stress depends on the initial axial strain condition. Nonetheless, when the main direction load becomes predominant, all tested wires converge to a common behavior. This observation allowed us to combine the results from critical current measurements under the loads exerted in both directions (axial and transverse), shedding some new light on the mechanisms behind critical current degradation.

Section: The Role Of Axial Strain In the Response Of The Wires To Transverse Loadsmentioning

confidence: 99%

Section: The Role Of Axial Strain In the Response Of The Wires To Transverse Loadsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of the initial axial strain state on the response to transverse stress of high-performance RRP Nb₃Sn wires

Troitino

Bagni

Barth

et al. 2021

“…The sensitivity of Nb 3 Sn conductor under transverse compressive stress at cryogenic temperature has been widely investigated in [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. This loading case is representative of the operation of magnets but not of the assembly process during which the pre-compression is applied at room temperature.…”

Section: Introductionmentioning

confidence: 99%

Effect of transverse compressive stress applied at room temperature on Nb₃Sn Rutherford cables

Lenoir,

Puthran,

Barth

et al. 2024

The accelerator magnets for the High Luminosity upgrade of the Large Hadron Collider (HL-LHC) use Nb3Sn conductor to achieve the required in-field performance. To sustain the Lorentz forces during operation, a pre-compression is applied to the coils during the fabrication of the magnet. This can lead to an irreversible degradation of the Nb3Sn conductor due to its mechanical sensitivity.In this study, the impact of the pre-compression applied to the conductor at room temperature is investigated using a reacted double-stack specimen made of two Nb3Sn Rutherford cables. The cables have a keystone angle and are stack with a non-inverted configuration, witout compensating the angle. The rectangular specimen is submitted to increasing transverse compressive stresses at room temperature applied perpendicularly to its width. The non-inverted configuration and the rectangular shape of the total specimen can thus lead to stress concentration. The pressure applied covers the range from 130 MPa to 190 MPa with a 10 MPa step increase. After each cumulated stress level, transport current measurements are performed in liquid helium and in background fields of up to 9.6 T in the FReSCa test station at CERN. Metallographic analyses of several samples are made at selected stress levels. Monotonic and cumulated stresses are applied and the impact of mechanical cycling is analysed. Procedures are specifically developed to minimize surface damage during samples’ preparation. The observations are compared with the electrical measurements in order to correlate the irreversible effect of the transverse pressure with the A15 damage state in the cross section.The transport current measurements of the double-stack specimen show degradation of critical current and n-value starting at respectively 170 MPa and 160 MPa cumulated loadings. However, cracks in the A15 phase are already observed in a metallographic sample subjected to 140 MPa.

“…One of the main challenges is the brittleness of the Nb 3 Sn conductor [5][6][7]. The assembly process is delicate as there is a risk of over compressing the coil in its collared coil structure.…”

Section: Introductionmentioning

confidence: 99%

Mechanical analysis of the Nb₃Sn 11 T dipole short models for the High Luminosity Large Hadron Collider

Bermúdez

Nilsson

Bottura

et al. 2019

For the Large Hadron Collider luminosity upgrade, two of the NbTi 8.3 T main bending dipoles will be replaced by two shorter Nb 3 Sn 11.2 T dipoles to create space for the installation of collimators in the dispersion suppression region. With the aim to verify the design features, several 2 m long 11 T models have been constructed and tested at CERN. During the fabrication and assembly of, so far, seven single and two double aperture short model magnets, several challenges were identified and tackled. These include reproducibility in coil fabrication and assembly procedure, as well as control of mechanical stresses in the conductor and surrounding structure. In order to limit coil over-compression and improve reproducibility, the cable insulation was re-optimized. In addition, a review of the collaring procedure of the 11 T magnet was launched with the goal of reducing the risk of conductor degradation due to excessive stress. In this paper, the main fabrication and assembly steps are described, including the description of the actions taken to resolve the identified weakness.