Review of high temperature superconducting flux pumps

High temperature superconducting (HTS) magnets conduct DC currents ranging from hundreds to tens of thousands of amperes. To achieve such DC output amplitudes, conventional power supplies are unsuitable, owing to their extreme cost, energy consumption, and bulkiness. The indispensable current leads of conventional power supplies carrying large DC current cause an extra heat leakage into the cryogenic system, thus increasing the number of required cryocoolers. A potential solution to tackle this problem, however, is to use HTS flux pumps that inject a large amount of DC current into the HTS magnet in a wireless fashion, thereby eliminating the need for current leads, and allow the magnets to work in the quasi-persistent current mode. Compared with the conventional power supplies, the flux pumps offer the advantages of low cost, low energy consumption, and compact size, etc., which essentially have broad application prospects in nuclear magnetic resonance (NMR/MRI), fusion, particle accelerators, superconducting electric machine, maglev train, etc. Over the last decade, a variety of HTS flux pumps have been invented with improved DC outputs, reaching over kilo-amperes. Moreover, those flux pumps have different working principles, structures and operation strategies. In this paper, we provide an in-depth review on the HTS flux pumps developed in the last decade. In particular, for the HTS travelling wave flux pumps and HTS transformer-rectifier flux pumps, the discussions are focused on their working principles and technical advances. In the end, we discuss the present applications of HTS flux pumps, along with their potential future applications.