Experimental testing of a modified active disturbance rejection control for microphonics reduction in a 9-cell TESLA superconducting cavity

This work shows the results obtained with a novel modified active disturbance rejection control (MADRC) algorithm when controlling the detuning of a 9-cell TESLA superconducting radio frequency cavity. This type of control is essential in SRF cavities with high loaded quality factors since they are extremely sensitive to detuning due to their extremely narrow bandwidth. The modification of the active disturbance rejection control is based on loop shaping techniques and confers ease of design and implementation, as well as an improved behavior in presence of delay. To begin with, a theoretical design of the controller based on an experimental transfer function of the cavity is carried out and its performance is compared with that of a proportional integral control. In this preliminary test, the simulation results indicate a remarkable performance superiority of the MADRC. Later, the controller is tested on a TESLA cavity validating both the MADRC algorithm and its design methodology, and achieving a peak detuning reduction of 63%, as well as an rms reduction of 80% with respect to the open loop.