Microphonics control for superconducting radio frequency cavities using a delay-resistant modification of the active disturbance rejection control

Abstract

The main objective of this thesis is to develop a feedback controller capable of reducing the peakdetuning of superconducting radiofrequency cavities being operated with high loaded quality factor.Detuning occurs when factors like mechanical vibrations and radiation pressure cause the cavity¿sresonance frequency to deviate from the desired operating frequency, leading to a significant degradationof the efficiency of the accelerator and, in extreme cases, may even cause operational failures. Thisdissertation deals in particular with microphonic detuning, which refers to any external mechanicalperturbations affecting the accelerating structure.For this purpose, a modification of the Active Disturbance Rejection Control (ADRC) is developed inorder to obtain an algorithm more resistant to time delay, without compromising its performance. Thisnew algorithm is based on a generalized extended state observer (GESO) that guarantees that thematching condition of the ADRC algorithm is allways met and allows open-loop frequency analysis ofthe system. In conjunction with this observer, a loop shaping compensator is also added, which is thecontrol element in charge of providing greater relative stability to the controlled system.The resulting controller is tested on a 9-cell TESLA cavity in the Horizontal-Bi-Cavity Teststand(HoBiCaT) of Helmholtz-Zentrum Berlin (HZB), obtaining great results