151 research outputs found
High-field thermal transport properties of REBCO coated conductors
The use of REBCO coated conductors is envisaged for many applications,
extending from power cables to high-field magnets. Whatever the case, thermal
properties of REBCO tapes play a key role for the stability of superconducting
devices. In this work, we present the first study on the longitudinal thermal
conductivity () of REBCO coated conductors in magnetic fields up to 19
T applied both parallelly and perpendicularly to the thermal-current direction.
Copper-stabilized tapes from six industrial manufacturers have been
investigated. We show that zero-field of coated conductors can be
calculated with an accuracy of from the residual resistivity ratio of
the stabilizer and the Cu/non-Cu ratio. Measurements performed at high fields
have allowed us to evaluate the consistency of the procedures generally used
for estimating in-field in the framework of the Wiedemann-Franz law
from an electrical characterization of the materials. In-field data are
intended to provide primary ingredients for the thermal stability analysis of
high-temperature superconductor-based magnets.Comment: Accepted for publication in Superconductor Science and Technolog
Thermal Conductivity of Industrial Nb3Sn Wires Fabricated by Various Techniques
We have developed a new experimental setup specifically designed for
measuring thermal conductivity on technical superconductors in the range of
temperatures from 3 to 330 K in magnetic fields up to 21 T. Three Nb3Sn wires,
produced by the powder in tube technique, the bronze route and the internal tin
restacked rod process, respectively, have been investigated. We show that, due
to the complexity of the architecture of these wires, direct measurement of
thermal conductivity is required for a correct estimation of thermal stability
in superconducting magnets.Comment: Accepted for publication in IEEE ASC 2012 Special Issu
An equation for the quench propagation velocity valid for high field magnet use of REBCO coated conductors
Based on a study of the thermophysical properties, we derived a practical
formula for the normal zone propagation velocity appropriate for
REBaCuO coated conductors in high magnetic fields. An
analytical expression to evaluate the current sharing temperature as a function
of the operating conditions is also proposed. The presented study has allowed
us to account for experimental results not fully understood in the framework of
the models widely used in the literature. In particular, we provided a
fundamental understanding of the experimental evidence that the normal zone
propagation velocity in REBaCuO coated conductors can be mainly
determined by the operating current, regardless of the applied field and
temperature
Thermal conductivity and stability of commercial MgB conductors
This paper presents a study of the thermal transport properties of MgB
tapes differing in architecture, stabilization and constituent materials. The
temperature and field dependence of thermal conductivity, , was
investigated both along the conductor and in the direction perpendicular to the
tape. These data provide fundamental input parameters to describe the 3D heat
diffusion process in a winding. Thermal transport properties - even in field -
are typically deduced using semi-empirical formulas based on the residual
resistivity ratio of the stabilizer measured in absence of magnetic field. The
accuracy of these procedures was evaluated comparing the calculated
values with the measured ones. Based on the experimental thermal conduction
properties and critical current surface we determined
the dependence of minimum quench energy and normal zone propagation velocity on
the operating parameters of the conductor. The correlation between thermal
properties and tape layout allowed us to provide information on how to optimize
the thermal stability of MgB conductors.Comment: Accepted for publication in Superconductor Science and Technolog
Transverse Thermal Conductivity of REBCO Coated Conductors
REBCO coated conductors (CCs) have the potential to widen considerably the
application areas of superconductivity. Quench protection of REBCO-based
devices represents one of the major obstacles to this expansion. Thermal
conductivity data are mandatory ingredients for quench simulation studies. In
particular, the transverse thermal conductivity () of the CC plays a
key role in case of quenches in superconducting magnets. In the present work,
we report of thermally stabilized REBCO CCs produced by different
manufacturers. We have measured on single CCs rather than on stacks
of soldered tapes, this excludes spurious contributions in the measurements. We
have found that the presence of the stabilizer at the tape edges in
Cu-electroplated CCs increases the overall . In the absence of this
effect, the overall thermal resistance is dominated by the substrate.Comment: ASC Charlotte 2014, IEEE Transactions on Applied Superconductivity
Vol. 25 Issue 3 JUNE 201
Temperature and time scaling of the peak-effect vortex configuration in FeTeSe
An extensive study of the magnetic properties of FeTeSe
crystals in the superconducting state is presented. We show that weak
collective pinning, originating from spatial variations of the charge carrier
mean free path ( pinning), rules in this superconductor. Our results
are compatible with the nanoscale phase separation observed on this compound
and indicate that in spite of the chemical inhomogeneity spatial fluctuations
of the critical temperature are not important for pinning. A power law
dependence of the magnetization vs time, generally interpreted as signature of
single vortex creep regime, is observed in magnetic fields up to . For
magnetic fields applied along the c axis of the crystal the magnetization
curves exhibit a clear peak effect whose position shifts when varying the
temperature, following the same dependence as observed in
YBaCuO. The time and temperature dependence of the peak
position has been investigated. We observe that the occurrence of the peak at a
given magnetic field determines a specific vortex configuration that is
independent on the temperature. This result indicates that the influence of the
temperature on the vortex-vortex and vortex-defect interactions leading to the
peak effect in FeTeSe is negligible in the explored range of
temperatures.Comment: Accepted for publication in Phys. Rev.
- …