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Effective resonance control of superconducting radio frequency (SRF) cavities is critical for large machines like LCLS-II, as failure to achieve proper control can result in increased RF power consumption, higher cryogenic heat loads, and increased costs. To address this challenge, we have developed a machine learning (ML) model based on the dynamic mode decomposition method to represent the forced cavity dynamics. Using this model, we designed a model predictive controller (MPC) and demonstrated through simulation that the MPC can effectively stabilize the amplitude and phase of SRF cavities using only a frequency actuator, even in the presence of multiple mechanical modes. The lightweight and explicit ML model makes the controller suitable for direct implementation on field-programmable gate arrays, unlocking the full potential of SRF linacs like LCLS-II, enabling higher beam power and energy, and also serving as an advanced motion controller for various applications, such as photon beamlines and storage rings. [ABSTRACT FROM AUTHOR]

Abstract: To drive future X-ray FELs, normal-conducting linacs with a wide range of rf are being considered. In this paper, we present accelerator structure and high power rf system designs at three rf (2.856GHz, 5.712GHz and 11.424GHz) that are optimized for single bunch and multi-bunch linac operation with very low beam loading. General scaling laws for the main linac parameters are derived to serve as guidelines to optimize such linacs at other frequencies. The linac costs at the three rf are also discussed. High rf linacs are shown to provide compact, low cost and reasonably efficient drivers for X-ray FELs. [Copyright &y& Elsevier]

An L-band (1.3 GHz) radio frequency (rf) waveguide system was assembled at SLAC to test components of a high power distribution scheme proposed for the International Linear Collider (ILC). All parts were made of aluminum and pressurized with dry nitrogen. The rf breakdown rate measured in this resonantly powered system is presented as a function of field level at different gas pressures and rf pulse widths (typically, only breakdown thresholds are reported.). The data are compared to predictions of a simple model which relates the breakdown phenomenon to the rate at which the free electron density builds in the gas. [ABSTRACT FROM AUTHOR]