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 ?
Though the Book of Common Prayer staked out a complex mediatory position within these possibi lities -- from its birth, there has been a critical current opposed to its theological and aesthetic traditionality -- the present analysis will focus on some foundational differences between Catholic and Prayerbook worship, and on the role played by language in them.
Extending this IBAD/pulsed-laser deposition approach in a continuous process, the Los Alamos researchers were able to produce meter-lengths of YBCO superconducting tapes with critical current exceeding 100 Amperes and current densities of one million Amperes per square centimeter at liquid nitrogen temperatures.
Buckyball compounds may also surpass their competitors in terms of critical current density, or the amount of current the superconductor can carry before losing zero resistance.
StudySync was honored to be an integral part of such an important initiative as NHM's VOTES Project, demonstrating the power of technology to bring students - and ideas - together around such critical current events such as the national election," said Robert Romano, CEO, BookheadEd Learning.
US patent (13/155,508) titled "Enhancing Critical Current Density of Cuprate Superconductors" discloses a method for enhancing the critical current density in superconductors by restricting the movement of Abrikosov (A) vortices, Josephson (J) vortices, or Abrikosov-Josephson (A-J) vortices using the half integer vortices associated with the d-wave symmetry present in the grain boundary.
An intercomparison of critical current determinations in a Nb3Sn superconductor was undertaken between laboratories within the Community.
Research and review studies shed light on areas such as transport properties of YBCO superconductors, large-area pulsed laser deposition of YBCO thin films, cube textured nickel-based substrates for YBCO coatings, and magnetic properties and critical current of YBCO superconductors.
The NIST data show that in repeated testing the critical current (the maximum current the conductor can carry) is degraded by only 1 % to 5 % at the benchmark 100 MPa stress level.
Four months ago, when two independent research groups reported the discovery of billions of spiral defects in superconducting thin films, both teams suggested that putting these defects, called screw dislocations, into wires might boost their current-carrying capacity, or critical current density, to that of thin films (SN: 4/6/91, p.
Insightful analysis on critical current and future issues is presented through detailed SCPT (strengths, challenges, prospects and threats /risks) analysis for each of the PESTLE segments.
As part of NIST's program to develop standard measurement techniques for superconductors, two NIST scientists have identified and studied a new source of misinterpretation in critical current measurements of superconductors.
Once the current exceeds a certain value known as the critical current, the material loses its ability to conduct electricity with zero resistance and no energy loss.

Full browser ?