The New Eddy Current Type Septum Magnets for Upgrading of Fast Extraction in Main Ring of J-PARC

Abstract

The J-PARC Main Ring (MR) is currently working on upgrading the machine power reach to 750 kW by increasing the beam repetition rate from 0.4 Hz to 0.78 Hz. This new operation mode is referred as "1 Hz" operation. The Fast eXtraction (FX) system in MR needs to upgrade to realize 1 Hz operation, and the improvement will be completed in 2021. The present FX Low-Field Septa (FX LF-Septa) which are conventional ones will be replaced with the new septa which is induced eddy current type (FX Eddy-Septa). The first FX Eddy-Septa system, which included the magnets and short pulse power supply (PS), was constructed in 2014. We have been studying the FX Eddy-Septa system to evaluate the stability of the output pulsed current and magnetic gap field since 2014. In winter of 2018, the 1 Hz operation test by using the two Main-chargers was conducted without any problem. The stability of the output pulsed current was 10 ppm. The leakage field was measured along the circulating beam line, and we found that the level of leakage field was still larger than our requirement. The PS has still several issues which must be solved. The switching time of the Main-charger to the Sub-charger must be reduced, the jitter of time lag between two discharge triggers must be eliminated, and the disagreement between the two current monitor systems must be solved.