Chemical soak to remove furnace contamination without disrupting surface oxide or removing bulk materials

Abstract

An improved method of removing furnace contamination on niobium cavities to increase the quality factor (Q0) and the accelerating gradient (Eacc) of SRF accelerator cavities. Performing a nitric soak at or below 70% concentration removes contamination which can't be removed by conventional sulfuric/HF EP, HF soaking, which in turn can improve both Q0 and RF accelerating gradients in niobium. The chemical soak can also remove contamination from a niobium surface without removing the native oxide or bulk niobium removals, such as after infusion or mid-T baking.

What is claimed is: 
     
         1 . A method of removing furnace contamination from the surface of an article of niobium (Nb) to increase the SRF quality factor (Q 0 ) and the accelerating gradient (Eacc) without removing the native oxide or the niobium, comprising soaking the Nb article in nitric acid (HNO3). 
     
     
         2 . The method of  claim 1 , comprising the nitric acid (HNO3) is at or below 70% concentration. 
     
     
         3 . A method of removing furnace contamination from the surface of an article of niobium (Nb), comprising:
 doping the Nb surface with nitrogen;   electropolishing (EP) the surface; and   soaking the Nb article in nitric acid.   
     
     
         4 . The method of  claim 3 , comprising the nitrogen doping comprises:
 applying nitrogen to the Nb article for at least 3 minutes; and   applying vacuum for at least 60 minutes.   
     
     
         5 . The method of  claim 4 , comprising the nitric acid is at or below 70% concentration. 
     
     
         6 . The method of  claim 5  comprising the niobium article is soaked at a temperature of at least 160° C. 
     
     
         7 . The method of  claim 5  comprising the niobium article is soaked at a temperature of 160° C. to 450° C. 
     
     
         8 . The method of  claim 7  comprising the niobium article is soaked while under a vacuum of less than 5 mbar. 
     
     
         9 . The method of  claim 7  comprising the niobium article is soaked while under a vacuum of 5-6 mbar. 
     
     
         10 . The method of  claim 2  comprising the niobium article is soaked at a temperature of at least 160° C. 
     
     
         11 . The method of  claim 2  comprising the niobium article is soaked at a temperature of 160° C. to 450° C. 
     
     
         12 . The method of  claim 11  comprising the niobium article is soaked while under a vacuum of less than 5 mbar. 
     
     
         13 . The method of  claim 11  comprising the niobium article is soaked while under a vacuum of 5-6 mbar.