Dielectric Resonator to Measure Surface Resistance of Accelerator Components at Room Temperature and 77 K

We measured the surface resistance of titanium, amorphous carbon, and nonevaporable getter (NEG) coatings on copper samples, representative of surface treatments of beam-facing components in the High-Luminosity Large Hadron Collider at CERN. Measurements were done at room temperature as well as at liquid nitrogen temperature (77 K) by means of a novel large dielectric resonator operating at 3.4 GHz. The impact of a 100 to 400 nm titanium layer or a 50-nm amorphous carbon layer was negligible both at room temperature and down to 77 K in comparison to copper, while a thick (1140 nm) NEG layer showed a measurable increase in the surface resistance, being more significant at low temperature. The dielectric resonator proved to be a useful tool to characterize the surface resistance of flat samples with different surface treatments and sizes up to 10 cm for accelerator applications. Furthermore, its construction and operation are much simpler compared to other test devices currently in use, and it can provide accurate experimental data for the evaluation of the beam coupling impedance.