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Critical state response in hard type II superconductors (comparison of transverse and longitudinal geometries)
Youssef, Ahmed Elmetwally ; Janů, Zdeněk (advisor) ; Koláček, Jan (referee) ; Gömöry, Fedor (referee)
In this work we have studied the Bean critical state model (BCSM) in hard type II superconductors. The study has been aimed towards the determination of the critical current density Jc and its temperature dependence using analyses of a temperature dependence of a magnetic susceptibility χac measured by a contactless method using SQUID magnetometer. We have compared the predictions of the BCSM for the four geometries: slab in a parallel field, long cylinder in an axial field, and disk and strip in a transverse field. The main interest of the present study is the χac of the superconducting thin films (disk and strip). We have measured the magnetic response of Nb thin films and second-generation high temperature superconductor YBa2Cu3Ox wire in a perpendicular AC field as a function of temperature as well as bulk NEG-123 sample in parallel magnetic field. We have presented a method of linking model and experimental susceptibility. The good agreement of experimental susceptibility with model of 2D disk allows noncontact estimation of the critical depinning current density and its temperature dependence. Harmonic analysis of the temperature dependence of the nonlinear χac gives excellent agreement with the susceptibility calculated on basis of 2D BCSM to disk.
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Critical state response in hard type II superconductors (comparison of transverse and longitudinal geometries)
Youssef, Ahmed Elmetwally ; Janů, Zdeněk (advisor) ; Koláček, Jan (referee) ; Gömöry, Fedor (referee)
In this work we have studied the Bean critical state model (BCSM) in hard type II superconductors. The study has been aimed towards the determination of the critical current density Jc and its temperature dependence using analyses of a temperature dependence of a magnetic susceptibility χac measured by a contactless method using SQUID magnetometer. We have compared the predictions of the BCSM for the four geometries: slab in a parallel field, long cylinder in an axial field, and disk and strip in a transverse field. The main interest of the present study is the χac of the superconducting thin films (disk and strip). We have measured the magnetic response of Nb thin films and second-generation high temperature superconductor YBa2Cu3Ox wire in a perpendicular AC field as a function of temperature as well as bulk NEG-123 sample in parallel magnetic field. We have presented a method of linking model and experimental susceptibility. The good agreement of experimental susceptibility with model of 2D disk allows noncontact estimation of the critical depinning current density and its temperature dependence. Harmonic analysis of the temperature dependence of the nonlinear χac gives excellent agreement with the susceptibility calculated on basis of 2D BCSM to disk.
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Kritický stav v tenkém Nb filmu
Youssef, A.E. ; Švindrych, Z. ; Hadač, J. ; Janů, Zdeněk
We present high resolution measurements of temperature dependence of low frequency ac magnetic susceptibility of superconducting Nb thin film in perpendicular time-varying periodic applied magnetic fields. We map this data, including harmonics, to the ac susceptibility calculated on basis of the complete analytical model of magnetization of thin superconducting disk in critical state. We find an excellent agreement between the measured and model data for temperatures up to 0.9997Tc
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