Superconducting flux pumps are the kind of devices which can generate direct current into superconducting circuit using external magnetic field. The key point is how to induce a DC voltage across the superconducting load by AC fields. Giaever [1] pointed out flux motion in superconductors will induce a DC voltage, and demonstrated a rectifier model which depended on breaking superconductivity. Klundert et al. [2, 3] in their review(s) described various configurations for flux pumps all of which relied on inducing the normal state in at least part of the superconductor. In this letter, following their work, we reveal that a variation in the resistivity of type II superconductors is sufficient to induce a DC voltage in flux pumps and it is not necessary to break superconductivity. This variation in resistivity is due to the fact that flux flow is influenced by current density, field intensity, and field rate of change. We propose a general circuit analogy for travelling wave flux pumps, and provide a mathematical analysis to explain the DC voltage. Several existing superconducting flux pumps which rely on the use of a travelling magnetic wave can be explained using the analysis enclosed. This work can also throw light on the design and optimization of flux pumps.

This paper examines the dynamics of the LiCl-KCl system over a range of temperatures in order to understand the local structure surrounding chlorine, which is the common ion in these systems, during molten salt pyro-processing. Chlorine-35 nuclear magnetic resonance (NMR) is sensitive to the local environments of the resonant nuclei and their motion on a diffusive timescale. Thus, it is a good probe of the atomic scale processes controlling the viscosities, diffusivities and conductivities of these molten salts. The average isotropic chemical shifts (((35)Cl)δ) and spin-lattice relaxation times (T1) of (35)Cl in (Li,K)Cl salt mixtures have been obtained over a compositional range of 0-100 mol% KCl with an interval of 10 mol% using high temperature nuclear magnetic resonance (NMR) spectroscopy from room temperature up to 890 °C. The ((35)Cl)δ in the two end member salts are consistent with the cation-anion radius ratio as previously measured on the solid halides and the average radius ratio of cation to anion, can be used to explain the variation of ((35)Cl)δ with composition. The quadrupolar interaction is found to be responsible for the spin-lattice relaxation of the (35)Cl, and the activation energies for T1 relaxation have been obtained for all compositions. The measured T1 ((35)Cl) activation energies do not vary linearly with composition and peak at 50% KCl, which also coincides with the Chemla point for this system. They also are in good agreement with the values from equivalent conductivity measurements. To investigate the response of the system to solutes, 8 wt% of CeCl3 was added to the pure LiCl as a surrogate actinide. The shift induced was 120 ppm and the activation energy for the T1 ((35)Cl) increased by a factor of four. This is a promising preliminary result for probing the effect of actinide dissolution on the dynamics of these pyro-processing salts.