6,774 research outputs found
Magnetostrictive behaviour of thin superconducting disks
Flux-pinning-induced stress and strain distributions in a thin disk
superconductor in a perpendicular magnetic field is analyzed. We calculate the
body forces, solve the magneto-elastic problem and derive formulas for all
stress and strain components, including the magnetostriction . The
flux and current density profiles in the disk are assumed to follow the Bean
model. During a cycle of the applied field the maximum tensile stress is found
to occur approximately midway between the maximum field and the remanent state.
An effective relationship between this overall maximum stress and the peak
field is found.Comment: 8 pages, 6 figures, submitted to Supercond. Sci. Technol., Proceed.
of MEM03 in Kyot
Oscillatory regimes of the thermomagnetic instability in superconducting films
The stability of superconducting films with respect to oscillatory precursor
modes for thermomag- netic avalanches is investigated theoretically. The
results for the onset threshold show that previous treatments of
non-oscillatory modes have predicted much higher thresholds. Thus, in film
supercon- ductors, oscillatory modes are far more likely to cause
thermomagnetic breakdown. This explains the experimental fact that flux
avalanches in film superconductors can occur even at very small ramping rates
of the applied magnetic field. Closed expressions for the threshold magnetic
field and temperature, as well oscillation frequency, are derived for different
regimes of the oscillatory thermomagnetic instability.Comment: 5 pages, 5 figure
Dendritic flux avalanches in rectangular superconducting films -- numerical simulations
Dendritic flux avalanches is a frequently encountered instability in the
vortex matter of type II superconducting films at low temperatures. Previously,
linear stability analysis has shown that such avalanches should be nucleated
where the flux penetration is deepest. To check this prediction we do numerical
simulations on a superconducting rectangle. We find that at low substrate
temperature the first avalanches appear exactly in the middle of the long
edges, in agreement with the predictions. At higher substrate temperature,
where there are no clear predictions from the theory, we find that the location
of the first avalanche is decided by fluctuations due to the randomly
distributed disorder.Comment: 3 pages, 2 figure
Dendritic flux patterns in MgB2 films
Magneto-opitcal studies of a c-oriented epitaxial MgB2 film with critical
current density 10^7 A/cm^2 demonstrate a breakdown of the critical state at
temperatures below 10 K [cond-mat/0104113]. Instead of conventional uniform and
gradual flux penetration in an applied magnetic field, we observe an abrupt
invasion of complex dendritic structures. When the applied field subsequently
decreases, similar dendritic structures of the return flux penetrate the film.
The static and dynamic properties of the dendrites are discussed.Comment: Accepted to Supercond. Sci. Techno
- …