Liquid Neon system and characterization of ac loss and quench propagation for MgB2 conductors


Bianchetti, Marco (2007) Liquid Neon system and characterization of ac loss and quench propagation for MgB2 conductors. University of Southampton, School of Engineering Sciences, Doctoral Thesis , 124pp.

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Description/Abstract

Magnesium diboride (MgB2) was found to have superconducting characteristics in January 2001
below 39K. The abundance and low cost of its components and the possibility to manufacture
long length of wires and tapes using the powder in tube technique makes this material a good
candidate for cheaper alternative to many low temperature superconductor application.

A closed system Neon liquefier and dedicated hybrid current leads have been designed to
investigate properties of MgB2 based conductors in liquid Neon in the temperature range from
24.5K to 31K. The system is capable of liquefying 3 litres of Ne and recover all the boil off. The
temperature of the liquid Ne can be adjusted by controlling the temperature of copper surface
extending in the Ne vessel. 900A hybrid current lead was designed and built using BSCCO
superconducting tapes at the lower end while the top end was constructed as a liquid nitrogen
cooled copper lead.

In the Ne cryostat transport AC loss measurements of a non magnetic NiCr sheathed and a
magnetic Ni sheathed Cu stabilized MgB2 tape have been conducted. Despite the NiCr alloy is
non-magnetic, the high temperature treatment of the superconductor results in the formation
of a magnetic layer at the interface with the superconducting core. For both samples the losses
are found to be dominated by the hysteresis losses of the magnetic layer and sheath. The
results are presented and analyzed.

The minimum propagation zone and the quench energy of a MgB2 superconducting wire has
been measured in Ne vapour environment. Our results show a good agreement with published
literature where the minimum propagation zone of MgB2 has been found to increase with the
transport current.

AC losses in external applied magnetic field have been measured on MgB2 samples using a
purposely built rig and sample holder employing sapphire fingers to effectively thermally link
the sample to a cold source, consequently eliminating the eddy current losses in the sample
holder. The losses of the MgB2 samples below Tc are dominated by the losses of the magnetic
sheath and are higher than the losses above Tc. Our measurements suggest that the losses in
the superconducting state are the result of an interaction between the ferromagnetic sheath
and the diamagnetic superconductor, where as the sample is cooled below Tc the field in the
outer magnetic sheath is increased.

Item Type: Thesis (Doctoral)
Subjects: T Technology > TP Chemical technology
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Q Science > QC Physics
Divisions: University Structure - Pre August 2011 > School of Engineering Sciences > Astronautics
ePrint ID: 65715
Date Deposited: 17 Mar 2009
Last Modified: 27 Mar 2014 18:47
URI: http://eprints.soton.ac.uk/id/eprint/65715

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