The superconducting magnet which is installed on a maglev vehicle suffers a disturbance of magnetic fluctuation from the ground coils. This magnetic disturbance has a frequency widely ranging from 0Hz to several hundred Hz which is proportional to the speed of maglev vehicle. We constructed the facilities which can simulate an actual electro-magnetic disturbance on the magnet in running and exercised electro-magnetic vibrating tests. It was revealed that an extreme increase of heat load on the inner vessel of the energized magnet was caused at a particular frequency. The initial amount of the heat load in these phenomena surpassed the capacity of the refrigerator installed in the tank of the superconducting magnet. So we have investigated into the causes of these phenomena and performed an experiment for confirming the effect of the improvement in a new setup. As a result, we could identify broadly three factors of heating and now we have good prospects of largely suppressing the heating by reducing the disturbance through the folded arrangement of the ground coils and structural improvement of the magnet. This paper describes the heating phenomena of a magnet under the electro-magnetic disturbance and the improvement for suppressing them as well as the historical background of maglev development.
High rigidity type superconducting magnet (SCM) is developed and tested by electromagnetic vibration simulator which simulate the actual running condition. To reduce the increase of heat load by the vibration of cryostat, several kind of design concepts are chosen. It is recognized by the experiment result that the most effective design concept is to increase the characteristic frequency in twisting mode of inner vessel with the high rigidity outer vessel.
Superconducting magnets on Maglev trains vibrate due to harmonic ripples of electromagnetic flux generated by ground coils. Heat load caused by vibration in the magnet, made in 1990, amounted to several tens of watts in the electromagnetic vibration test. This was mainly because AC loss was induced in the helium vessel housing the superconducting coil, due to relative vibration between the aluminum thermal shield and the coil. The heat load caused by vibration should be strictly restricted to less than 4W due to limited cryogenic refrigeration capacity. The heat load has been tested using electromagnetic flux ripples for a superconducting magnet model of one coil which corresponds to 1/4 of an actual magnet. The flux ripples simulate the 6th harmonic of the actual ground levitation coil. Some ideas to reduce the heat load were tried for the magnet model, such as high resistance thermal radiation shield, high rigidity of vacuum vessel, high purity copper plating on the helium vessel. As a result, these ideas were effective, and the maximum heat load due to vibration was restrained to less than 4W per magnet for one coil magnet model.