RRR Characteristics for SRF Cavities

TL;DR

This paper investigates how electron beam welding conditions affect the residual resistance ratio (RRR) in superconducting cavities, which is crucial for their performance in a new heavy ion accelerator project.

Contribution

It provides an analysis of RRR degradation mechanisms during electron beam welding of niobium cavities, highlighting key welding parameters impacting RRR preservation.

Findings

RRR degrades during electron beam welding due to impurity incorporation.

Welding power, speed, and vacuum level significantly influence RRR degradation.

Maintaining RRR above a certain threshold is essential for cavity performance.

Abstract

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.