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Applications: Metrology
Published in David A. Cardwell, David C. Larbalestier, Aleksander I. Braginski, Handbook of Superconductivity, 2022
John Gallop, Ling Hao, Alain Rüfenacht
The use of superconductors in solenoids allows current densities to be much higher than for conventional conductors due to zero Joule heating. Additional ‘shim’ windings may be used to convert the field profile of a simple uniformly wound solenoid into a highly homogeneous distribution where, over a small central volume, the magnetic field varies by no more than 1 part in 108 or 1 part in 109. Furthermore, the ability to provide persistent supercurrents in both the main coil and the subsidiary windings means that a particular homogeneous field value may be maintained with a precision of 1 in 109 per hour or even greater (especially at field levels below 10 T). Persistent current superconducting solenoids can reduce the need for highly stable magnet current supplies, although in this case the stability over time of the magnetic field relies on the physical stability of the solenoid dimensions.
Introduction to Superconducting Devices
Published in Raja Sekhar Dondapati, High-Temperature Superconducting Devices for Energy Applications, 2020
The zero resistance characteristics of a superconductor refer to the phenomenon of abrupt disappearance of resistance at a certain temperature, known as the critical temperature of a superconductor (Tc). In such conditions, the superconductor can transport direct current (DC) without resistance. Further, if a closed loop is formed in which a current is induced, the current, known as “persistent current”, will flow indefinitely without any signs of decay for several years. The upper limit of resistivity measured for “persistent current” experiment is less than 10–27 Ω-m, whereas a good conventional conductor, such as copper, has a resistivity of 10–10 Ω-m at 4.2 K. Thus, the resistivity of copper is more than 17 orders of magnitude, higher than that of a superconductor [5]. A typical dependence of resistance on the temperature of a superconductor and a normal conductor is shown in Figure 1.2. The resistance of a superconductor drops to zero when the temperature reduces to a certain value below the critical temperature (Tc), which is due to the non-scattering by crystal lattice, resulting in no dissipation of energy when operating with DC. Whereas for a normal conductor, upon decreasing temperature, some resistance in the material is observed.
Early Experiments and Phenomenological Theories
Published in R. D. Parks, Superconductivity, 2018
The central point of the London theory is that the supercurrent is always determined by the local magnetic field. The Meissner effect is interpreted to mean that the diamagnetic currents induced when a simply connected superconductor is cooled through Tc in an applied field are identical with the super-currents induced when a field is applied after cooling through Tc in zero field. A persistent current has the same physical relation to the magnetic field it produces as an externally applied supercurrent in a straight wire does to its field; in both cases the magnetic field sustains the current. It is inadequate to consider a superconductor just as a perfect conductor (which would lead, in F. London’s words, to “a continuum of non-equilibrium states to which one must attribute persistent currents of a truly acrobatic stability”), or as a perfect diamagnet, for this would not describe correctly the persistent current in a ring.
Study of thermomagnetic properties of the diatomic particle using hyperbolic function position dependent mass under the external hyperbolic magnetic and AB force
Published in Molecular Physics, 2022
Suci Faniandari, A. Suparmi, C. Cari
To summarize, we have solved the approximate solution of the Schrodinger equation with hyperbolic function position-dependent mass for a symmetrical Modified Poschl-Teller potential by using the method of Laplace transform. We consider the system influenced by the external hyperbolic magnetic and Aharonov-Bohm (AB) forces. The second-order differential equation of the Schrodinger equation is reduced to the first-order differential equation and so the eigenfunction and eigen energy values are obtained. We also analyzed the behavior of the bound state energy levels for the various value of the potential parameter, mass parameter, external magnetic force, and AB force. It showed that the energy value depends on the quantum number, potential parameter, mass of the molecule, and magnetic field strength. Meanwhile, the magnetic flux density (AB Force) doesn’t have a significant effect on the energy value. The quantum number and the potential parameter are most apparently affected by the change in energy level, then the magnetic field strength is affected by the decrease in the energy level of the particle considered in this system. The thermos-magnetic properties of the system also have been carried out, involving the vibrational mean energy, free energy, entropy, heat capacity, magnetization, magnetic susceptibility, and persistent current. We have analyzed the behavior of the H2, LiH, and HCl diatomic molecules through the simulation in the high range of temperature. These results can motivate the further study of molecular physics for several molecules.
Persistent currents in the presence of the radial electric fields of charged rods and off-centre positively and negatively charged impurities
Published in Philosophical Magazine, 2021
H. K. Salehani, Davood Haji Taghi Tehrani, M. Solaimani
The effect of the screening parameter α in Equation (1) has been shown in Figure 5. This figure presents the variation of the persistent current as a function of the magnetic flux ϕ for an SQR system. Also, we assumed x = 0.3, R1 = 160 nm and R2 = 200 nm. Thereafter, in the presented figures, we assume these initial suppositions unless otherwise is stated. As this figure shows, as the screening parameter increases the persistent current also increases. As we know, increasing the screening parameter delocalises the electron around the impurity. Therefore, as the electron becomes delocalised, the persistent current increases. Therefore, we can make the hypothesis that the delocalisation of the electron in any other manner may also lead to increasing the persistent current. This can be a proposal for the next investigations in this field of study. Another feature, in this figure, is that by increasing the screening parameter, the persistent current oscillations start to exhibit a saw-tooth structure. In lower screening parameters, the persistent current is a sinusoidal function of the magnetic flux.