  SRF niobium cavities are the building blocks of modern accelerators for
scientific applications. Lower surface resistance, higher fields, and high
operating temperatures advance the reach of the future accelerators for
scientific discovery as well as potentially enabling cost-effective industrial
solutions. We describe the design and performance of an Nb$_{3}$Sn coating
system that converts the inner surface of niobium cavities to Nb$_{3}$Sn film.
Niobium surface, heated by radiation from the niobium retort, is exposed to Sn
and SnCl$_{2}$ vapor during the heat cycle, which results in about 2 $\mu$m
Nb$_{3}$Sn film on the niobium surface. Film composition and structure as well
as RF properties with 1-cell R\&D cavities and 5-cell practical accelerator
cavities are presented.
