  The first heavy ion accelerator is being constructed by the rare isotope
science project (RISP) launched by the Institute of Basic Science (IBS) in
South Korea. Four different types of superconducting cavities were designed,
and prototypes were fabricated such as a quarter wave resonator (QWR), a half
wave resonator (HWR) and a single spoke resonator (SSR). One of the critical
factors determining performances of the superconducting cavities is a residual
resistance ratio (RRR). The RRR values essentially represent how much niobium
is pure and how fast niobium can transmit heat as well. In general, the RRR
degrades during electron beam welding due to the impurity incorporation. Thus
it is important to maintain RRR above a certain value at which a niobium cavity
shows target performance. In this study, RRR degradation related with electron
beam welding conditions, for example, welding power, welding speed, and vacuum
level will be discussed.
