Electro-mechanical characterization of MgB₂wires for the Superconducting Link Project at CERN

Abstract

In previous years, the R & D program between CERN and Columbus Superconductors SpA led to the development of several configurations of MgB2 wires. The aim was to achieve excellent superconducting properties in high-current MgB2 cables for the HL-LHC upgrade. In addition to good electrical performance, the superconductor shall have good mechanical strength in view of the stresses during operation (Lorenz forces and thermal contraction) and handling (tension and bending) during cabling and installation at room temperature. Thus, the study of the mechanical properties of MgB2 wires is crucial for the cable design and its functional use. In the present work we report on the electro-mechanical characterization of ex situ processed composite MgB2 wires. Tensile tests (critical current versus strain) were carried out at 4.2 K and in a 3 T external field by means of a purpose-built bespoke device to determine the irreversible strain limit of the wire. The minimum bending radius of the wire was calculated taking into account the dependence of the critical current with the strain and it was then used to obtain the minimum twist pitch of MgB2 wires in the cable. Strands extracted from cables having different configurations were tested to quantify the critical current degradation. The Young’s modulus of the composite wire was measured at room temperature. Finally, all measured mechanical parameters will be used to optimize an 18-strand MgB2 cable configuration.

Increase of the critical current density of MgB2 superconducting bulk samples by means of methylene blue dye additions

“…Magnesium diboride (MgB2), being made of abundant and non-toxic constituent elements, and thanks to its transition temperature (Tc) close to 40 K, is among the most promising superconducting materials for large scale applications. In the form of wires or bulk samples, it has already been used for demonstration units, including high field magnets [1,2], energy storage devices [3,4], high power cables [5], racetrack coils [6], etc. In spite of these successful realizations, further improvements of the critical current density (jc) performance of MgB2 wires and bulk samples under the application of magnetic fields are desirable since jc tends to be severely suppressed when a magnetic field is acting on the material.…”

Critical current density improvements in MgB 2 superconducting bulk samples by K 2 CO 3 additions

“…For several applications involving high magnetic fields such as magnets [1,2], energy storage devices [3,4], high power cables [5], etc., exploiting the superconducting properties of MgB 2 on a large-scale commercial level requires further improvements of the critical current density (j c ) performance of wires and bulk samples, because this parameter tends to be severely suppressed as soon as a magnetic field is acting on the material. This is especially important if MgB 2 is meant to be used at an operation temperature of 20 K. Besides the addition of nanoparticles acting as flux pinning centers [6][7][8], doping on the boron sites in the MgB 2 crystal lattice has been found to be effective in enhancing the pinning force and hence the j c of MgB 2 under high magnetic fields [9][10][11][12][13][14][15][16].…”

Design of a 20-MW Fully Superconducting Wind Turbine Generator to Minimize the Levelized Cost of Energy

“…In this article, r t is considered half of the tape thickness. The tension strain is chosen as 0.3%, which is the upper limit where the critical current density remains unchanged due to the bending stresses [11]. With those assumptions, the minimum bending radius is 108 mm.…”