Diagnostics based on Higher order mode port signals
"Parasitical" use of HOM couplers. Image credit: Universitat Rostock
Higher order mode (HOM) couplers are a crucial part of many superconducting cavities since unwanted modes, which are excited by the beam, need to be damped effectively. EuCARD WP10 task 5 is predominantly dealing with studies on diagnostics based on HOM port signals. This task is carried out jointly with the teams around Roger Jones (University of Manchester, speaker) and Nicoleta Baboi (DESY).
Monitoring the HOM port signals as a by-product of the HOM damping offers the possibility to determine the transversal offset, the total charge of the bunch, etc. with little additional hardware.
One major concern of the ongoing studies is to predict the theoretical accuracy of the diagnostic system in the context of uncertainties such as perturbations of the cavity from the design shape. The entire investigation is based on three pillars: First, experiments at the FLASH facility at DESY in Hamburg are undertaken with the focus on the third harmonic module ACC39. Second, numerical simulations are performed using existing commercial programs such as CST MICROWAVE STUDIO® and in-house codes. Third, new computational methods are developed and implemented. In this context, a method to determine wake fields in large structures by means of decomposition techniques is constructed. Moreover, a generalized perturbation theory is in development which determines a set of eigenmodes of the perturbed geometry based on a set of eigenmodes of the unperturbed shape. Overall, the research efforts are aiming for a sophisticated understanding of diagnostics based on HOM port signals. The long term goal is the equipment of current and future machines with diagnostics based on HOMs.
