Effect of bunch shape on electron-proton instability

The instability caused by the electron cloud effect (ECE) may set an upper limit to beam intensity in proton storage rings. This instability is potentially a major obstacle to the full intensity operation, at 1.5e14 protons per pulse, of the Spallation Neutron Source (SNS). High intensity experiments have been done with different sets of parameters that affect the electron-proton (e-p) instability, of which bunch intensity and bunch shape are considered as two main factors. In the experiment, the phase and amplitude of the second harmonic RF cavity are used to modify the bunch shape. Analysis is made on the experimental results to understand the impact of bunch shape on beam stability. Benchmark of the e-p model is ongoing to address the threshold of bunch shape more accurately.