1,990 research outputs found
Magnetostriction of a Superconductor: -Results from the Critical-State Model
In many cases, the critical-state theory can be treated as a suffi ciently
accurate approximation for the modelling of the magnetic properties of
superconductors. In the present work, the magnetostrictive hysteresis is
computed for a quite general case of the modified Kim-Anderson model. The
results obtained reproduce many features of the giant magnetostriction
(butterfly-shaped curves) reported in the literature for measurements made on
single-crystal samples of the high-temperature superconductor
. It is shown that addition of a contribution to the
magnetostriction in the superconducting state which is of similar origin as in
the normal state, offers a broader phenomenological interpretation of the
complex magnetostriction hysteresis found in such heavy-fermion compounds as
, or .Comment: 9 LaTeX pages, 4 Postscript figures, WWW version available at
http://is.dal.ca/~zkoziol/super.htm
MgB2 conductors for dc and ac applications
The paper presents discussion on up to date results on MgB2 conductors from
the point of view of their future dc and ac applications. Basic physical
parameters of MgB2 compound relevant to conductors are introduced. Different
conductor preparation methods and conductor architectures are presented and
attainable critical current densities discussed. Some numerical results on
critical currents and ac losses of future multifilamentary MgB2 conductors with
magnetic cladding of their filaments are given. Recently observed anomalous
decrease of ac susceptibility at 50 K in copper clad Powder-in-tube, PIT, MgB2
wires is presented.Comment: Paper presented at EUCAS'01 conference, Copenhagen, 26-30 August 200
Degenerate ground state and anomalous flux hysteresis in an YBa2Cu3O7 grain boundary r.f. SQUID
We report measurements of the flux hysteresis curves and trapped flux
distribution in an YBa2Cu3O7 r.f. SQUID containing two closely spaced grain
boundary Josephson junctions in parallel. Broadening of the flux distribution
from T = 15 K to 30 K is followed by a bifurcation at T = 35 K which
corresponds to a degenerate ground state. Above T ~ 40 K the bifurcation
disappears, the flux distribution narrows significantly and small secondary
loops appear in the hysteresis curves. This behaviour can be modelled
qualitatively if we assume a temperature dependent second harmonic term in the
current-phase relationship of the junctions.Comment: 10 pages, 7 figure
Parametrised Preisach Modelling of Hysteresis in High Temperature Superconductors
We present a parametrised Preisach-type model that describes the hysteresis exhibited by the high temperature superconductors (HTSC); hysteresis is the main cause for losses in the subcritical domain. The parametrised model, in combination with electrical measurements, is independent of geometry, number of filaments and other physical measures, and is identified by a novel method that uses electrical lock-in (loss) measurement technique, which greatly enhances the signal to noise ratio. Identification results from measurements on Bi-2223 multi-filamentary tapes are presented. We have further derived exact models for the hysteretic losses in strip and elliptic geometry strips, where the energy losses were calculated by Norris. The paper contains analysis of the Preisach Model, of its losses and of the suggested parametrisation
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