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Design and characterization of a LTS flux pump system for possible satellite application

Even, L. (2016) Design and characterization of a LTS flux pump system for possible satellite application. Bachelor's Thesis, Physics.

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In this bachelor project research is performed on the design of a prototype low temperature superconducting (LTS) flux pump system. With such a system a superconducting electromagnet can be charged to high currents, while only a low current power supply and cryogenic wiring is necessary. The flux pump could find potential as an application in the SAFARI instrument for the SPICA satellite, but it can also be used for cryogenic energy storage or for off-setting a magnetic field. As a satellite application the flux pump can reduce parasitic heat load on the cold stages of the satellite. Within this thesis we continued the work on an existing flux pump design from a previous bachelor project. This design had previously shown some essential performance characteristics of a flux pump system, but the actual flux pumping was not observed. In this thesis work we investigated the possible causes of this and implemented improvements. These improvements have resulted in a working flux pump system. The main improvement (which was found in a late stage of the project) was the correction of the winding orientation of a secondary coil in the transformer. Other improvements are: (1) the optimization of the transformer cooling, such that higher critical currents in the primary transformer superconducting wire could be achieved, and (2) the increase of the self-inductance of the primary coil of the transformer by replacing the original aluminum transformer core (that will induce eddy currents) by a Vespel polyamide core. For the characterization of the transformer performance we have used a two-phase lock-in measurement technique to determine the self-inductance and mutual inductance of the primary and secondary coils as a function of frequency. The final flux pumping system (V3.0) operates at 4 K, and consists of a transformer with a 4950 turn primary coil (Lp = 4,4mH self-inductance), a 2 x 10 turn secondary coil (Ls = 0,5 µH, and a 900 turn load coil with an estimated self-inductance around 13,5mH), all made with superconducting wire. The current in the load coil is monitored by measuring the magnetic field that is generated by the coil with a fluxgate meter. The primary coil has been operated with a maximum current (ramp) of 0;5A (500 mA/s). The measured and calculated current gain of the flux pump are both around 0;16mA per cycle for a 50mA primary current. With this system a current of at least several amperes should be achievable in the load coil (resulting in a magnetic field in the order of at least dozens of milliteslas), but we have limited ourselves to a maximum of 60mA, because of limitations in the range of the flux gate sensor (not higher than 590 µT). The coupling factor (0 ≤ k ≤ 1) describes the coupling between the primary and secondary side in a transformer, where a value close to 1 would be ideal. For the final flux pumping system k is estimated to be around 0,45.

Item Type: Thesis (Bachelor's Thesis)
Degree programme: Physics
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 15 Feb 2018 08:24
Last Modified: 15 Feb 2018 08:24

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