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Description
The flat-top pulsed magnet field (FTPMF) can achieve the fields above 40 T with long duration, which enables the development of the terahertz gyrotron of 1THz with the operation width longer than 1 ms. The performance of the gyrotron is significantly influenced by the stability of FTPMF. Using a small compensation coil built into the bore of the magnet is a practical method to achieve the stability of FTPMF better than 100 ppm. However, the fields generated by the compensation coil can lead to the distortion of the magnetic fields distribution, which will cause the gyrotron to be unable to operate. Therefore, in this paper, we proposed a multi-stage coil to compensate the pulsed magnetic field in order to achieve high stability of FTPMF without affecting the magnetic distribution on the axis of the gyrotron. Firstly, in order not to change the magnetic distribution, the multi-stage coil need to generate the field with the same distribution on the axis as that generated by the magnet. An optimization model based on particle swarm optimization algorithm (PSO) is established to design the number of turns, dimensions, and current proportion of each coil in the multi-stage coil. Secondly, the coupling between each coil and the magnet will influence the currents in each coil. To eliminate the coupling, the external series coupling transformers is utilized to overcome the mutual inductance. Finally, a 40 T flat-top pulsed magnetic field with the stability better than 100 ppm and without changing the magnetic distribution on the axis is achieved.
