Speaker
Description
A cryogenic, HV conditioning system integrated in a stand-alone cryocooler is operated at FREIA laboratory in Uppsala in order to investigate the fundamental mechanisms of field emission and breakdown nucleation. A series of high-field measurements has been carried out with pairs of metal electrodes (copper, niobium and titanium) at temperatures ranging from ambient down to 4K.
The cryogenic capability of the system give unique opportunity to observe variations of the behavior of the electrodes conditioned and tested in cold vs warm state. We previously reported on the notable increase of the field holding capability of the cooled electrodes that rises with decreasing temperatures.
In the recent experiments, we investigated further the state of the surface during conditioning by detailed field emission experiments and analysis of the accompanied residual gas outflow. We have also designed and are currently implementing additional diagnostics of the conditioning process. After the conditioning, the morphology of the surface has been studied as well, looking for differences on the surface between cold and warm conditioning samples. Different surface modifications were found on cathode conditioned at cold, with many atypical BD spots of a star-like shape. The number of atypical spots increased significantly with decreased temperatures.
In the presentation, we will report on these and other experimental results from Uppsala, and provide our interpretation. The data should help to refine theoretical models and potentially discriminate between various underlying physical mechanisms, thus eventually improving our understanding of BD phenomena.
