Investigation of the effect of low temperature baking on frequency and RF field dependence of surface resistance using multi-mode coaxial cavity

Understanding how the surface resistance of superconducting niobium cavities depends on frequency, temperature, and RF field is essential for advancing next-generation accelerators. Most previous studies used single-mode elliptical cavities, which do not allow to measure the surface resistance as a function of frequency. To address this, a bulk Nb half-wave coaxial cavity was built at Old Dominion University that supports multiple TEM modes on the same surface, enabling systematic comparison across frequencies within a single cavity. Its broad frequency range (0.3 to 1.3 GHz) and well-defined field distribution allow accurate evaluation of the quality factor and dissipation under cryogenic conditions. Here, we present the RF measurement results of the cavity that underwent baseline surface treatment consisting of buffered chemical polishing followed by low-temperature baking, guiding the development of processing techniques to achieve high accelerating gradients.