Magnetothermal Instabilities Research Articles

The range of giant flux instabilities in the plane in hard superconductors: calculations and experiment

We have studied magnetothermal instabilities, giant flux jumps, both theoretically and experimentally. Magnetostriction and magnetization hysteresis loops with flux jumps were calculated over a wide range of experimental parameters employing two critical-state models: the Kim-Anderson model and the exponential model. The influence of the magnetic history on the flux jumps' magnetostriction and magnetization were investigated for the LaSrCuO single crystal. The shape of the unstable region of the critical state in the temperature-magnetic field plane was constructed from calculations and experimental results. In the Kim-Anderson model H-T diagrams of flux instabilities agree well with experimental results on HTSC single-crystal LaSrCuO and experimental results on LTSC niobium.

Magnetothermal instabilities in an organic superconductor

We have studied the occurrence of magnetothermal instabilities in a $$\kappa - {(BEDT - TTF)_2}Cu[N{(CN)_2}]Br$$ single crystal during field sweep magnetization experiments, equivalent to short time relaxation studies. We find instability behaviour in good agreement with a recent model by Mints, for a non-linear E(J) characteristic. In particular, we find that a decrease of the dynamic relaxation rate, characterizing the effective activation energy, precedes the unstable regime. We point out formal analogies between such instabilities and the general predictions for flux avalanches.

H–T phase diagram for the giant magnetic flux jumps in low temperature superconductors and high temperature superconductors

We have studied magnetothermal instabilities both theoretically and experimentally. Magnetostriction and magnetization hysteresis loops with flux jumps were calculated over a wide range of experimental parameters employing three critical state models: the original Bean model, the Kim–Anderson model, and the exponential model. The influence of the magnetic prehistory on the flux jumps, magnetostriction, and the magnetization was investigated for the LaSrCuO crystal. H–T diagrams of flux instabilities were constructed from calculation and from experimental results. One can see good qualitative agreement between these two diagrams.

Reversible mechanism of magnetothermal instabilities in melt-textured YBaCuO

The anisotropy of the development of instabilities in the metl-textured YBaCuO samples with remanent magnetization of 600 emu/g has been studied in a magnetic field up to 12 T. Large 500 emu/g jumps of the magnetic moment of the sample due to the development of the magnetothermal instability have been observed. A giant (10 −4) magnetostriction caused by the magnetic flux pinning has been revealed. Stabilization of the critical state of the sample by reversal of magnetization has been found. However, when the sample is heated to temperatures higher than 100 K and subsequently cooled the magnetic jumps restore completely. A new reversible mechanism of instability generation based on the phenomenon reversibility of plastic deformations of high-temperature superconductors (HTS) is proposed to explain the regeneration of critical state instability.

Observation of magneto-thermal instabilities in (YxTm1?x)Ba2Cu3O7 single crystals in pulsed magnetic field magnetization measurements

The understanding of flux jumps in the high temperature superconductors is of importance since the occurrence of these jumps may limit the perspectives of the practical use of these materials. In this work we present the experimental study of the role of heavy ion irradiation in stabilizing the HTSC against flux jumps by comparing un-irradiated and 7.5 · 1010 Kr-ion/cm2 irradiated (YxTm1−x)Ba2Cu3O7 single crystals. Using pulsed field magnetization measurements, we have applied broad range of field sweep rates from 0.1T/s up to 1800 T/s to investigate the behavior of the flux jumps. The observed flux jumps, which may be attributed to thermal instabilities, are incomplete and have different amplitudes. The flux jumps strongly depend on the magnetic field, on the magneto-thermal history of the sample, on the magnetic field sweep rate, on the critical current density jc, on the temperature and on the thermal contact with the bath in which the sample is immersed.

Magnetothermal instabilities in YBa 2Cu 3O 7

We have studied the magnetothermal instabilities in YBa 2Cu 3O 7 by using thermal and magnetic measurements. These magnetothermal instabilities consist of flux jumps and temperature jumps, and quasiperiodic oscillations of the temperature and magnetization of the sample. We have interpreted these instabilities with the model primarily introduced by R.G. Mints but taking into account the form of the dissipated power we have found experimentally. The influence of the sweep rate of the applied magnetic field on the appearance of the first flux jump and on the periodicity of the oscillations has been studied. The results are in good agreement with the proposed model.

The relevance of the ballooning approximation for magnetic, thermal, and coalesced magnetothermal instabilities

Approximate solutions of the linearized non-adiabatic MHD equations, obtained using the ballooning method, are compared with ‘exact’ numerical solutions of the full equations (including the effects of optically thin plasma radiation). It is shown that the standard ballooning method, developed within the framework of ideal linear MHD, can be generalized to non-ideal linear MHD. The localized (ballooning) spectrum has to be used with caution, but can give valuable (though limited) information on non-ideal stability.