A Rotating Flux Pump Employing a Magnetic Circuit and a Stabilized Coated Conductor HTS Stator

Abstract

High temperature superconductor (HTS) magnet systems usually employ metal current leads which bridge between the cryogenic environment and room temperature. Such current leads are the dominant heat load for these magnet systems due to a combination of electrical resistance and heat conduction. HTS flux pumps enable large currents to be injected into a HTS magnet circuit without this heat load. We present results from an axialtype HTS mechanically rotating flux pump which employs a ferromagnetic circuit and a Cu-stabilized coated conductor (CC) HTS stator. We show the device can be described by a simple circuit model which was previously used to describe barrel-type flux pumps, where the model comprises an internal resistance due to dynamic resistance and a DC voltage source. Unlike previously reported devices, we show the internal resistance and DC voltage in the flux pump are not exactly proportional to frequency, and we ascribe this to the presence of eddy currents. We also show that this axial-type flux pump has superior current injection capability over barrel-type flux pumps which do not incorporate a magnetic circuit.

Energy balance, efficiency and operational limits of the dynamo type flux pump

“…From figures 6 and 7 a linear dependence of V average (I) is observed over a wide range of impressed currents. This trend is widely confirmed in experiments [4][5][6][7][8], and in the considered case applies for an operating current approximately within the interval from −100 A to +100 A (see figure 7). Thus, within this linear interval, the following expression can be introduced for the average terminal voltage…”

“…The average motional electromotive force produced by the PM onto the elements (thin wires) of the discretization during one rotation cycle is shown in figure 3. This is the voltage impressed by the voltage sources of the FEM-based equivalent circuit of figure 2, corresponding to terms u h in equation (6). They apply both for the current driven operation (figure 2(a)) and for the RL load (figure 2(b)).…”

“…Compared to Low-temperature superconductors (LTS), Hightemperature superconductors (HTS) magnets suffer greater magnetic field decay when operating in persistent current mode due to the low n-value and the higher joint resistance. In order to maintain a persistent current in HTS coils, connection to an external power supply at ambient temperature is survey provided by van der Klundert and ten Kate was published [1,2], different flux pumps concepts have been proposed [3][4][5][6][7][8][9][10][11]. An updated perspective of flux pumps topologies and operation can be found in [12,13].…”

“…We report that the value at the center can be considered instead of the average on the hth element for defining coefficients m hk , r hh and u h in equation(6). Such an approach, consisting of assuming as weighting function the Dirac delta function δ(r h ) at the center of the elements instead of the element wise uniform weighting function 1/S h , do not produce significant difference in the results.…”

Influence of ferromagnetic slice on the charging performance of a through-wall HTS flux pump employing a magnetic coupler

“…Due to the fact that the magnetic field distribution in HTS tapes would be changed by the FM materials [45], we applied a piece of permalloy slice in the experiments, aiming at studying the influence it may bring. We have used an oscilloscope to monitor the open-circuit voltage waveform, as is shown in figure 7, from which we found that there are only tiny differences between the waveforms when the tape was immersed in the LN 2 and was put at room temperature, but leads to a totally different result [46].…”