Rf Commissioning Of The Compact Energy Recovery Linac Superconducting Cavities In Pulse Mode

At the KEK compact energy recovery linac (cERL), a new beam line to produce radioisotopes (RIs) was constructed. To increase the beam energy for RI production, we proposed to switch the operation mode from continuous-wave mode to pulse mode. The first commissioning test of the cERL superconducting radio frequency (RF) cavities operated in pulse mode was therefore carried out. The RF pulse pattern for each cavity was carefully selected according to the corresponding cavity's loaded Q and the capabilities of the power sources. A modified feedforward table was applied to reduce the peak reflected power at the power coupler. In addition, a filling on resonance approach that aims to reduce the required incident power during the filling time due to the existence of the Lorentz force detuning was adopted. The slow drift of the pulse-to-pulse detuning on the flat top of an RF pulse was successfully compensated for by a piezo feedback system. In this paper, we present the results related to the cERL pulse mode operation. The measured RF stabilities and beam energy stability in the cERL beam commissioning are presented as well.