Experimental study on on-line cleaning of Ar/O2 plasma on metal niobium surface

Abstract:

Hydrocarbon contamination in superconducting niobium cavity results in the decrease of surface work function of niobium, field emission and the deterioration of accelerating gradient of superconducting cavity. After working for a period of time, it is necessary to clean the hydrocarbon contamination to ensure its normal running. At present, the cleaning effect after plasma processing cannot be judged accurately and timely to control the cleaning cut-off point. In addition, the off-line testing may cause some secondary pollution.Therefore, we present a plasma cleaning and on-line monitoring device based on electrostatic quadrupole plasma (EQP) mass spectrometer and Kelvin probe. The plasma cleaning and residual gas monitoring were successfully integrated and put into use. During the experiment, the changes of cleaning byproducts and work function were monitored online. It was proved that the Ar/O2 mixed plasma produced by the inductively coupled plasma source with a plasma density of 1016~1017m-3 could effectively remove hydrocarbon contaminations from niobium surface and make oxidation modification on niobium surface, raising the work function from 4.0 eV to 5.3 eV.