Critical Current

critical current

[′krid·ə·kəl ′kər·ənt]
(solid-state physics)
The current in a superconductive material above which the material is normal and below which the material is superconducting, at a specified temperature and in the absence of external magnetic fields.

Critical Current


(in superconductors), the maximum value of the sustained direct current in a superconducting specimen at which the substance of the specimen passed into the normal, nonsuperconducting state. Since the substance in its normal state has a finite electric resistance, dissipation of the energy in the current takes place after the transition, thus heating the specimen.

In large superconductors of the first kind whose dimensions are considerably greater than the penetration depth of a magnetic field, the critical current Ic corresponds to the current that creates the critical magnetic field Hc on the surface of the superconductor. In this case the superconductor passes into an intermediate state, where part of it is in the normal state and part is in the superconducting state. While the current is present, the interfaces between the superconducting and the normal regions are in motion. Because of the Meissner effect, the magnetic field varies, an induction electric field develops, and energy dissipation occurs in the conductor.

In the case of the second kind of superconductors two values of critical current (Ic,1 and Ic,2) are distinguished. In an ideal superconductor (which contains no lattice defects) at Ic,1 the magnetic induction becomes nonzero and the magnetic field penetrates the superconductor. The penetrating field is in the form of filaments with a quantized magnetic flux, which are surrounded by circulating superconducting currents (vortex filaments). The energy dissipation in this case is associated with the time variation of the magnetic field caused by movement of the vortex filaments and with the corresponding induction electric field. In actual superconductors of the second kind (with lattice defects), an ohmic resistance develops when Ic,2 > Ic, 1, because the defects interfere with the movement of the vortex filaments.


References in periodicals archive ?
both the investigation and characterization of individual josephson junctions, arrays of josephson junctions and superconducting microwave circuits, superconducting tunnel junction detectors, semiconductor deep discharge breakdown, superconducting tunnel junctions, bandgap variations, and josephson current density, anisotropy of phonon propagation in single crystals as well as the defect mapping in single crystals, the mapping of flux tubes frozen in superconductors, the distribution of the critical current density and critical temperature in superconductors or superconducting layers play a role.
Compared with the calculated value of the critical amplitude density [[delta].sub.CC1] used in the experiment the damped sinusoidal current pulse [i.sub.p](t) which equals to [[delta].sub.CC1] [approximately equal to] []/[S.sub.CC1] [approximately equal to] 205 kA/3.34 [mm.sup.2] [approximately equal to] 61.4 kA/[mm.sup.2], the obtained experimental value of the critical current density [[delta].sub.CC1] differs from it by about 8 %.
Supreme Court members have evolved into "moral umpires" on critical current social and political issues.
The forum addresses some of the most critical current Internet policy issues, clustered into eight core themes: cybersecurity; trust and privacy; digital inclusion and accessibility; emerging technologies; evolution of internet governance, human rights, gender and youth; development, innovation and economic issues; media and content; and technical and operational topics.
The forum addresses some of the most critical current Internet policy issues, clustered into eight core themes: cybersecurity, trust u8206?and privacy; digital inclusion and accessibility; emerging technologies; evolution of u8206?internet governance; human rights, gender and youth; development, innovation and u8206?economic issues; media and content; and technical and operational topics.u8206?
On assuming office, Imran Khan went on his maiden foreign trip to the kingdom, amid speculation that he would ask the Saudis for help in meeting a critical current account deficit at home but nothing materialised.
However, when the load current is larger than a critical current ([I.sub.LC]), which depends on the power efficiency, a switching pulse of constant frequency is output, and the variation of the duty ratio provides an expected output that depends on the line and load regulations.
Dr Chua then took a swipe at the current MCA leadership for its poor performance on critical current issues, saying the party showed neither courage nor political wisdom.
With the development in the properties of high temperature superconducting (HTS) conductors, the HTS magnet could be considered as potential Tokamak magnet components with the advantages of higher operation temperature and critical current density [1-3].
Since the critical current [I.sub.c] of superconducting tapes depends on both the magnetic field's intensity and direction, it is of fundamental importance to optimize the tape distribution within the CICC in order to reduce the self-field degradation on [I.sub.c].
The two experiments which were performed in [LN.sub.2] were to examine the critical current of heat shrink insulated HTS tapes and to evaluate the dielectric strength of the various wall thickness of the heat shrinks discussed above.
This thus minimizes the probability of faulty switching and simultaneously assures an exact and robust detection of a critical current path, e.g.

Full browser ?