Effect of bending-magnet power-supply ripple on the beam performance in the Pohang Light Source

The 36 bending magnets in the Pohang Light Source storage ring are connected in series to a single power supply. The bending magnet power supply has a structure of 12 pulse Silicon-Controlled Retifier (SCR) rectifiers, and the rectified voltage is supplied to the bending magnets through a LC filter. Experimental users of bending magnets and undulator beam lines require unperturbed orbits for operation. A beam signal that was affected by the resonant component of the LC filter in the bending magnet power supply was detected in the beam lines, so the LC filter in the bending magnet power supply was changed to a structure with a (LC + RC) filter in order to suppress the resonant component that affected the beam quality. The performance of the current regulator was also improved. Thereafter, the current ripple in the magnet power supply was greatly reduced, and the current stability was improved. We discuss the performance of the modified magnet power supply system at the Pohang Light Source and its effects on the beam properties.