Revamp and Reactivation of a Niobium Furnace at DESY

For research in the field of heat treatments of superconducting cavities, a Niobium ultra-high vacuum furnace built in 1992 – originally used for the titanisation of 1.3 GHz nine-cell cavities - and later shut down was revamped and reactivated. A significant addition is the ability to run the furnace in partial pressure mode with nitrogen. The furnace is connected directly to the ISO4 area of the clean room for cavity handling. At room temperature vacuum values of around 3e-8 mbar are achieved; at 1200°C the achieved pressure is 2.5e-7 mbar The revision included the replacement of the complete control system and a partial renewal of the pump technology. The internal mounting structures are optimized for single-cell operation including tandem operation consisting of two single-cell cavities and corresponding accessories such as samples and caps for the cavities. The installation of additional thermocouples for a detailed monitoring of the temperature curves is also possible at the mounting structure. Due to the furnace design, the location and the strict routines in handling, very high purity levels are achieved in comparison to similar set-ups and hence provide a mighty tool for SRF cavity R&D

Medium Temperature Treatments of Superconducting Radio Frequency Cavities at DESY

Over the last years several different approaches to increase the performance of superconducting radio frequency (SRF) cavities by heat treatments have been developed and tested. At DESY, the R&D aims for cavities with enlarged quality factors while maintaining high accelerating gradients, since an envisaged upgrade of the European XFEL requires both. For this purpose, medium temperature (mid-T) treatments around 300 °C seem to be very promising. Lately, the furnace infrastructure at DESY was refurbished and now a niobium-retort furnace capable of carrying 1.3 GHz nine- cell cavities can be used for R&D studies. Vertical test results of single-cell cavities treated in this furnace at medium temperatures are presented and compared to four cavities treated similarly in a furnace at the company Zanon Research & Innovation Srl (Zanon). All mentioned cavities show enlarged quality factors but at the same time reduced gradients compared to their reference measurements before the mid-T treatment. The DESY treatments were accompanied by small niobium samples for surface analyses, which are also presented. Furthermore, the influence of post-treatment high pressure water rinsings is studied