Sources of Error in AC Losses Measurement Using V-I Method

A significant cryogenic load is generated in rapidly-cycling superconducting magnets due to ac losses. This load should not be excessive, otherwise cryogenic system will not be able to evacuate heat and magnet will quench. To verify magnet design and to know real cryogenic load the test of ac losses has to be performed. Electrical and calorimetric methods can be used for this purpose. The calorimetric method is slower because it requires stabilization of cryogenic system. The electrical method called V-I is faster and it can be applied to any magnet independent of its cooling schemes. With this method ac losses are measured directly and results are provided on-line. However, the electrical method is considered more error prone, mainly due to the fact that power factor of superconducting magnets is close to zero.