Fault Analysis of In-Vessel Compression Coils in HFRC

A field-reversed configuration (FRC) experiment device named HUST-FRC (HFRC) is constructed at Huazhong University of Science and Technology, where the fast magnetic compression of FRC will be investigated. 22 in-vessel compression coils are employed to generate a 0.5 T pulsed magnetic field within 50 mu s in a cylinder region with a diameter of 800 mm, which rapidly compresses the FRC to improve its density and temperature. The coils consist of 16 middle coils in the middle region and 6 mirror coils at both ends. It is difficult to ensure that the in-vessel coils all fire in every discharge experiment, especially when the coil system operates in a high voltage (similar to 0 kV) and pulsed current (similar to 110 kA/50 mu s) environment. Coil faults affect the current waveforms in other normal coils and the magnetic field distribution, which may increase their electromagnetic forces and even destabilize the structure. In this article, we investigate the influences of the coil faults on the current waveforms and electromagnetic forces. First, the reasons why the coil faults affect other coil circuits are analyzed through a complex coupled circuit model. Then the above influences are specifically analyzed through the multi-field coupled simulations. For the current waveforms in normal coils, other coil faults can lead to increased peak current and earlier rise times due to the strong electromagnetic coupling among the coils. The electromagnetic forces in the normal coils do not increase with the increased peak currents because the magnetic field decreases due to other faulty coils. Moreover, the analysis shows that the electromagnetic force in coil C-8 increases dramatically due to the change in the magnetic field distribution which is caused by the mirror coil faults.