High precision measurement of transient magnetic field and compensation of eddy current effect for magnets

Japan Proton Accelerator Research Complex (J-PARC) is a joint project between Japan Atomic Energy Agency (JAEA) and High Energy Accelerator Research Organization (KEK) which aims to achieve a MW-class proton accelerator facility. One of the promising solutions for increasing the beam power is to fasten the repetition rate of synchrotron from current rating of 2.6 sec to 1 sec in the future. For this purpose, a new magnet power supply with higher repetition rate is now under development. But one of the serious concerns for faster repetition rate of magnets is the effects of eddy-current. Longitudinally leaked magnetic field generates an eddy-current at the end-plates of magnet. The amplitude, or the seriousness, of the eddy-current is a linear function of ramp-up speed for excitation current. As a compensation method for the eddy-current, we have proposed to introduce a transfer function from excitation current to magnetic field. This transfer function is implemented in the feedback system of magnet power supply. The deviation of the magnetic field due to the eddy-current is drastically reduced with this method. In this article, operational results from POP experiment with the new feedback system for eddy-current compensation is reviewed. (author)