Magnetic Field Mapping and Excitation Test in Vacuum for the Kicker Magnet in J-PARC RCS

Abstract

Installation of the kicker magnets in the extraction section of the RCS in J-PARC facility was completed. They extract a proton beam accelerated up to 3GeV. Since high voltage of 30 kV, which corresponds to 60 kV for charging the pulse forming line, is applied to the magnet every 40 msec, they are installed in vacuum chambers to prevent the electrical breakdown. However, magnetic field mapping is difficult in vacuum. Therefore, we performed the mapping in the air with applying one third of the operational voltage after checking linear dependence of magnetic field to exciting current. A short search coil on the 3-axis stages was used in the magnetic field mapping. The results showed that the good uniformity was achieved in the whole aperture. The magnetic field distribution of the same type of kicker magnet was in good agreement with each other. The excitation test with the operational charging voltage of 60 kV was also performed in vacuum. At the first stage, we were bothered by the electric breakdown. It was noticed that the reduction of outgassing rate by baking was very effective to suppress the discharge. And the continuous excitation was found to have a conditioning effect for the stable operation.