The China Spallation Neutron Source (CSNS) facility began operation in 2018. By 2020, its accelerator achieved the design power of 100kW and currently operates at a power of 160kW. This year, the power upgrade project (CSNS-Ⅱ) has been launched to meet the growing scientific demands. Our goal is to enhance the accelerator power to 500kW primarily by increasing the beam current. A comprehensive suite of beam diagnostics has been developed to support commissioning and operation of the accelerator at higher intensities. In this paper, we first review the commissioning and operational status of the existing linac, and then outline the new requirements for the linac upgrade.

The China Spallation Neutron Source Rapid Cycling Synchrotron (CSNS-RCS) is the first high-intensity pulsed proton accelerator in China and the fourth in the world. The space charge effect is a key factor limiting power enhancement. Measuring the frequency shift induced by the space charge effect is an important method for studying this phenomenon. In our experiments, we varied the beam current by adjusting the injection pulse length and chopping rate. Using a combination of narrow-band filtering and Fast Fourier Transform (FFT) techniques, we successfully observed a tune shift of approximately 0.02 induced by a beam power of 140 kW. These experimental results were compared with simulation outcomes, showing good agreement.