Superconducting radio-frequency virtual cavity for control algorithms debugging

Superconducting radio-frequency (SRF) cavities are one of the most important elements in modern particle accelerators as they are used for beam acceleration, bunch manipulation, bunch focusing and defocusing, etc. Nevertheless, the availability of these complex structures prior to their installation in the accelerator is limited, either due to a lack of a real cavity or due to the time needed for the experiment setup (vacuum, cryogenics, cabling, etc.), and thus it can block or delay the development of new algorithms such as low level RF control, quench detection, etc. In this paper, we present a hardware virtual cavity to be used in hardware-in-the-loop simulations. The system implements a cavity electrical model for the transmitted and reflected voltages and more advanced features such as mechanical vibration modes driven by Lorentz-force detuning or external microphonics, hard quenches, and the Q-slope. As viewed from the RF input and output, this virtual cavity acts like a real SRF cavity and can replace such a system in early-stage debugging and operation of ancillary control systems.