Theoretical Analysis and Design Consideration of Advanced Linear Type Magnetic Flux Pump
As a current compensator, we already developed a linear type magnetic flux pump (LTMFP) that is comprised of DC coils, three phase armature coils, an LTS Nb foil and laminated linear slots. The LTMFP produced a homopolar traveling magnetic field with DC bias current and 3-phase armature current and then, a pumping current is generated in the closed superconducting loop. In this study, we have proposed an advanced LTMFP which can easily produce homopolar traveling magnetic field with the combination of a permanent magnet and the AC armature current. Since the permanent magnets have replaced DC coils in the system, its structure and operation are simplified. As well as, the heating loss of the advanced LTMFP is reduced due to the permanent magnet compared with the LTMFP. From this reason, we confirmed that the advanced LTMFP has more simplified and efficient operation compared with already developed magnetic flux pumps. This paper describes the structure and operating principle of the advanced LTMFP. As well as, the distributions of electromagnetic-thermal analysis of the LTS Nb foil were calculated based on the finite element method (FEM). Thus, in order to realize the homopolar traveling magnetic field, appropriately designing parameters of the combination of AC current and the permanent magnet were obtained.
Current Pumping Performance of Linear-Type Magnetic Flux Pump With Use of Feedback Control Circuit System
It has already been investigated that current pumping of the linear-type magnetic flux pump (LTMFP) is controlled by frequency of 3-phase inverter. In this paper, based on these operating characteristics, a current compensator, which is composed of a LTMFP and a feedback control circuit system, has been introduced to compensate for the persistent current decay of the superconducting magnet. From the experiment, the current compensator has been demonstrated with the toroidal assembly of six Nb-Ti magnets 543 mH under the operating load current at 10 A
Electrical resistivity and peak effect in superconducting niobium
The flux flow resistivity ρf has been measured in foils of high purity niobium as a function of magnetic field and temperature. The magnetic field dependence of ρf just belowHC2 is much stronger than predicted by the recent theory of Maki for the pure limit. NearHC2 a peak in the critical current is observed that is independent of any voltage criterion.