Sponsors of converts to Catholicism

A conversion presumably severs the spiritual ties with one's baptismal godparents. I am reading about a convert from Russian Orthodoxy to Roman Catholicism, who apparently converted around age 20 and was confirmed around age 50. The confirmation, his only surviving sacramental record, names a godfather that he could not possibly have met until he was an adult. In a comment, curiousdannii reveals that the term of art is "sponsor" (thanks!). Do converts to Catholicism always have exactly one sponsor? Does sponsorship differ from godparenthood? When do they get the sponsor?