Improvement of the Micro-pulse Structure for Top-up Operation at the Pohang Light Source

The beam current of the storage ring slowly decreases with time and is filled by periodic injection. The top-up operation uses a short time-interval injection to keep the current roughly constant. The injection efficiency in the top-up operation should be high in order to reduce the radiation caused by beam loss. In the previous design, the beam loss could not be eliminated because the electron pulse generated by the electron gun was longer than the RF bucket. To suppress the loss, we reduced the length of the gun pulse to 0.25-ns full width at half maximum, which is a fourth of the previous length. Additionally, the RF phases of the ring and the linac were synchronized to optimize the micro-pulse structure. The micro-pulse structure with synchrotron motion and RF synchronism was measured at the Pohang Light Source (PLS) by using a streak camera. A tracking simulation of the pre-injector is also presented.