Investigation of Niobium Surface Roughness and Hydrogen Content with Different Polishing Conditions for Performance Recovery of Superconducting QWRs in JAEA Tokai-Tandem Accelerator

抄録

The effect of the different polishing conditions for niobium has been investigated as the basic data for polishing the superconducting quarter-wave resonators (QWRs) in the booster linac of the Tokai-tandem accelerator. Surface roughness and desorbed hydrogen amount of niobium samples with different polishing conditions such as polishing method (electropolishing: EP or chemical polishing: CP), polishing thickness, and electrode location, have been measured. For the hydrogen amount measurement, thermal desorption spectroscopy has been performed. The electrode arrangement in the EP to avoid hydrogen bubbles hitting the niobium surface is found to be important to obtain a smooth surface and less hydrogen content. The large polishing thickness resulted in a large amount of hydrogen content in the niobium or large surface roughness in the case of both EP and CP. The EP without hitting the hydrogen bubbles and with appropriate polished thickness will be the best solution for the actual polishing of the QWRs.