Critical current density, temperature dependence

Critical current density also depends on magnetic field, decreasing monotonically to zero at the upper critical field Hc2 (16-17). In YBaCuO the slope of Hc2 with temperature is unusually large, of order 2 T/K when field is applied parallel to the predominant conduction planes of the structure (18-19). This implies record values (up to 200 T has been estimated) for the upper critical field at low temperatures and opens up the possibility of very high field magnets. 

Critical care analytes, measuring, 24 55 Critical cooling rate, of steel, 23 283 Critical current density, 23 821-823, 825 optimization of, 23 829 in PIT conductors, 23 833-834 temperature and field dependence of, 23 847-848... 

The strong inverse dependence of critical current density on magnetic field at 77 K is a limitation associated with Bi-2223 tape. This necessitates operation at lower temperatures for certain applications (e.g. electromagnets) when the cable is subjected to strong magnetic fields. This limitation does not arise with the (RE)BCO system and intensive efforts are being made to manufacture suitable tapes. 

Figure 7 Temperature dependence of the relative values of the critical current density Jq T), critical field BdT), energy gap Eg, density of superconducting electrons ng, and penetration depth X (T) in the Type II superconducting state below the transition temperature Tc...

A portion of the film on SrTi03 shown in fig. 13(b) was patterned into a 16 urn wide line by reactive ion etdiing to measure the critical current density and for other magnetotransport measurements. Figure 14 shows the temperature dependence of the critical current density, J. It can been seen that at 77 K and in zero field, a current density of 0.69 x 10 A/cm is measured. The film critical current density is greater than 4 x 10 A/cstr at 50 K and in a field of 14 Tesla. More detailed magnetotransport results will be mentioned later. 

As discussed in Chapter 4, the passivation potential and the passivation critical current density of stainless steel alloys depend upon the stabdity ofCr203. At temperatures higher than 1000-1200 °C, Cr203 forms volatile Cr03, which drastically decreases the alloy resistance to oxidation and its protectiveness [9,10]. The vapor pressure for oxides of refractory metals above 1000 °C are presented in Fig. 11.2 as Arrhenius plots of log (Pmo) vs. 1/T at constant oxygen pressure or log(po2) [8]-... 

Critical current densities on the order of 10 A cm at 77 K in zero field were measured on BSCCO thin films. In Fig. 4.2-46 the field dependence of 7c of a B12212 film is shown for two temperatures [2.90] and Fig.4.2-47 demonstrates the Jc(B, T) dependence of a B12223 film [2.87]. In magnetic fields aligned parallel to the plane of the film, that is perpendicular to the c axis of the crystal structure, 7c is practically independent on the field strength, even at higher temperatures such as 60 K. The reasons for this behavior are discussed below in connection with the Jc(B, T) correlation of wires and tapes. 

Shown in fig. 16 is the magnetic field dependence of the critical current density for the IBAD and RABiTS based YBCO coated samples recently produced at LANL and ORNL, respectively. These coated samples operated in the liquid nitrogen temperature range clearly outperform the metallic superconductors (NbTi, NbjSn) at 4.2 K. Furthermore, even in the worst field direction H c), and for temperatures below 65 K, the short sample YBCO coated conductors operated in a 8-tesla background field have at least an order of magnitude higher Jc than pre-commercial BSCCO-2223 wire with no applied field. 

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