First Principles Modeling of RFQ Cooling System and Resonant Frequency Responses for Fermilab’s PIP-II Injector Test

In this paper we develop an a priori method for simulating dynamic resonant frequency and temperature responses in a radio frequency quadrupole (RFQ) and its associated water-based cooling system respectively. Our model provides a computationally efficient means to evaluate the transient response of the RFQ over a large range of system parameters. The model was constructed prior to the delivery of the PIP-II Injector Test RFQ and was used to aid in the design of the water-based cooling system, data acquisition system, and resonance control system. Now that the model has been validated with experimental data, it can confidently be used to aid in the design of future RFQ resonance controllers and their associated water-based cooling systems. Without any empirical fitting, it has demonstrated the ability to predict absolute temperature and frequency changes to 11% accuracy on average, and relative changes to 7% accuracy.