Hydrogen Q-disease and electropolishing

Abstract

To find out the mechanism of the hydrogen absorption during electropolishing (EP), degree of hydrogen Q-disease of an L-band niobium (RRR (Residual Resistivity Ratio) = 200) single-cell cavity was compared between 1) continuous EP, 2) intermittent EP and 3) dipping into EP solution. It was found that hydrogen Q-disease did not occur in case 1) and occurred in cases 2) and 3). It was also found that with the niobium (RRR = 200) samples treated by the same way as above 1), 2), 3), hydrogen absorption was not observed in case 1) and was observed in cases 2) and 3). During the measurement of the cavity performance, it was noticed that a baking (130 C, 48 hr) was helpful to ease the seriousness of the hydrogen Q-disease. Concentration of the hydrogen was measured on the niobium samples that was treated with EP removing different amount of surface material (after hydrogen absorption through dipping into acid solution) and the results suggested that the absorbed hydrogen was localized in the surface layer of the samples.