Southern Advanced Photon Source (SAPS) is a 3.5GeV fourth-generation storage ring light source, considered to construction in Guangdong province of china, adjacent to the China Spallation Neutron Source(CSNS). Its natural emittance of the beam is close to the diffraction limit. Since the dynamic aperture of SAPS is far smaller than the physical aperture in the low emittance storage ring, on-axis swap-out injection scheme was adapted. Several couple sets of superfast kickers and nanosecond pulsers are needed. Due to the RF-frequency in the ring is 166.7 MHz, the gap of adjacent bunches is 6ns. In order to realize bunch-by-bunch control, the pulsers’ duration needs to be shorter than twice the minimum bunch spacing, which is a big challenge for SAPS. A prototype of fast nanosecond pulser based on semiconductor opening switch (SOS) was developed. A two-stage magnetic pulse compression system was used to pumping the SOS, which can provide with forward and reverse current of several hundreds of amperes. In this condition, the cutoff time of SOS can be reach several nanoseconds, which could meet the requirements of SAPS. The performance of the prototype can produce a pulse at 50Ω, with FWHM （50%-50%）of 5.6ns，bottom width(10%-10%) <12ns，an amplitude of 18kV. In this paper, the design, simulation and test results are presented.

In CSNS, there are more than 350 devices in the accelerator power supply system, which respectively provide precise excitation current for the magnet load. Therefore, the stable operation of the power supply is an important prerequisite to ensure the beam quality, and also one of the necessary conditions for the normal operation of the CSNS. In accelerator power system, digital controller is widely used because of its flexibility and reliability. However, with the accumulation of running time, the failure of power supply caused by the fault of the digital controller often occurs, which affects the operation efficiency of the accelerator. Through the analysis and detection of the failed digital controller, it is found that the failure is basically caused by the optocoupler failure. In this paper, firstly, by dividing the digital controller into functional modules, it is equivalent to series system. According to the reliability principle of series system, the failure of any part will lead to the failure of the whole system. Secondly, according to the nature of the optical coupling failure is revealed, the reliability model of the controller considering the optical coupling failure is established, and the overall life evaluation of the controller is obtained. Finally, for the failure caused by optocoupler failure, a redundancy strategy is proposed for this part to improve the reliability.