| The pulsed high magnetic field,a powerful tool for modern basic scientific research,is extensively applied to solid-state physics,chemistry,medicine,plasma science,highenergy physics and other multidisciplinary fields.In order to meet the needs of scientific research in different fields,the pulsed high magnetic field has derived different branches,such as pulses with flat-top,long-duration,high-strength,or a high repetition rate,among which,the repetitive pulsed high magnetic field(RPHMF)matters considerably in scientific research and modern industrial applications,such as neutron diffraction and magnetic refrigeration.The RPHMF is divided into two types,i.e.,burst type and continuous type,according to its waveform type.With the continuous deepening of related research,the RPHMF is moving towards the direction of high repetition frequency.There are challenges for both power supplies and magnets as the RPHMF is being achieved.In the generating process of the RPHMF,there exists serious energy loss on the magnet and the line caused by the Joule.However,given the power limitation of the primary energy device in the power supply system,the lost energy is difficult to be replenished in a rather short time,which limits the repetition frequency.In addition,the large amount of Joule heat leads to the dramatic increase of the magnet temperature.The magnet structure is generally required to have a space for convective heat exchange with the cooling medium to prevent the magnet from overheating.However,the coupling effect of the high magnetic field and the large current exposes the magnet to huge electromagnetic stress,which requires a compact magnet structure to ensure the mechanical stability,making it difficult to develop a high-field fast-cooling magnet satisfying such contradictory design requirements,thereby further increasing the difficulty in realizing the RPHMF at a high repetition.In order to realize the RPHMF at a high repetition rate,the systematic work of theory-prototypeexperiment,with the core device(power supply and magnet)of the pulsed high magnetic field system taken as the research object,is carried out on the following three aspects:(i)Study on the high-field fast-cooling pulsed magnet;(ii)Study on the multi-module parallel sequential power supply scheme for generating burst high frequency repetitive pulsed magnetic field;and(iii)Study on the energy feedback multi-module parallel sequential power supply scheme for generating continuous high repetition frequency pulsed magnetic field.For the fast-cooling pulsed magnet,the experimental test was used for clarifying the heat transfer characteristics of the microchannel from the perspective of the boiling heat transfer mechanism of liquid nitrogen.The heat transfer coefficient curve of the microchannel in liquid nitrogen was obtained based on the test platform.Then,taking the heat transfer coefficient curve as the third boundary condition in the microchannel heat transfer model,a multi-physics coupling model of the electromagnetic-thermal-structure of the pulsed magnet was hereby established,which reveals the influence of the number and spatial distribution of the microchannel on the heat dissipation efficiency of the magnet.Based on the influence mechanism,a design method of multi-microchannel fast-cooled pulsed magnets was proposed.Finally,a fast-cooled magnet was wound by combining two new processes of radial slotting of the flange and staggered the distribution of cooling channels.The magnet was subjected to a discharge test with a 3.2 m F capacitive power supply,and the peak value of the magnetic field reached 41.18 T at 20.5 k V.A battery power platform with an output voltage of 225 V was built to test the thermal performance of the magnet.The cooling time of the magnet from 305 K to 90 K is 186 s,which is only 12 s different from the simulation calculation,and the cooling efficiency increases nearly 10 times compared with the magnet without cooling channels.For the burst RPHMF,the timing control method of a parallel modular pulse circuit was firstly proposed,and the timing control strategy for generating explosive repetitive pulse strong magnetic field was clarified;secondly,the influence law of magnet resistance and freewheeling resistance on magnetic field waveform was clarified,and the voltage factor adjustment strategy and freewheeling resistance value principle were proposed,which significantly improves the consistency of repetitive pulse waveform and ensures the safety of system device operation.Then,the calculation method of the discharge scheme was proposed by synthesizing many influencing factors such as the number of repeated pulses,the resistance of the freewheeling resistance,the repetition frequency,the field strength,the pulse duration,and the thermal performance of the magnet,and the burst repetition with the highest parameter of 60 Hz/22 T is realized.The diversified repetitive pulses of single and bipolar with multiple magnetic field peaks are also realized according to the controllable characteristics of the polarity of the power module and the amplitude of the charging voltage;finally,a magnetic property test system for high-coercivity magnetic materials under the high magnetic field of bipolar repetitive pulses with attenuation amplitude was designed according to the needs of scientific experiments,and the Sm Co5nano-magnetic material with an ultra-high coercivity of 5731.2 k A/m was found in the environment of the maximum peak 18 T pulsed magnetic field,setting a new record for the coercivity of permanent magnet materials.At the same time,it is also proven that the burst RPHMF achieves sweeping rates in multiple ranges due to its waveform controllability,serving as a powerful tool for studying magneto dynamic behavior.For the continuous RPHMF,according to the energy distribution characteristics of the burst RPHMF generated by the parallel modular pulse circuit scheme,a parallel energy feedback modular circuit topology combined with the dual resonant pulse circuit was proposed,and a 20 T/10 Hz system scheme was designed using the circuit topology;then,in order to verify the feasibility of the parallel energy feedback modular magnetic field scheme,a dual resonant module prototype system with a magnetic field greater than 2 T and a frequency greater than 10 Hz was designed.The pulsed magnet,pulse transformer and high-frequency series resonant charger in the system were developed and optimized;finally,a dual-resonance module prototype test platform was constructed and the continuous RPHMF with 2.6 T/12 Hz was achieved,proving the efficiency of the parallel modular magnetic field scheme with dual resonant energy feedback technology to improve the repetition rate to n×12 Hz(n denotes the number of power modules),and forging a technical foundation for the development of continuous 20 T-level RPHMF at a high repetition rate on large-scale devices. |
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