Measurement of beam loading at the SNS superconducting linac for a beam with β<1

When a beam passes through superconducting cavities, it excites beam induced fields in the cavities. A systematic study is performed to study the beam loading effects with β<1 beam on the β=0.81 superconducting cavities of the Spallation Neutron Source (SNS) linac. The analysis indicates that the shunt impedance equation is still valid even for a beam with β well below 1. It is also shown that the induced field level is consistent with the estimation and its effect on the beam dynamics is consistent with the model.