  Superconducting RF is a key technology for future particle accelerators, now
relying on advanced surfaces beyond bulk Nb for a leap in performance and
efficiency. The SRF thin film strategy aims at transforming the current SRF
technology by using highly functional materials, addressing all the necessary
functions. The community is deploying efforts in three research thrusts to
develop next-generation thin-film based cavities. Nb on Cu cavities are
developed to perform as good as or better than bulk Nb at reduced cost and with
better thermal stability. Recent results showing improved accelerating field
and dramatically reduced Q slope show their potential for many applications.
The second research thrust is to develop cavities coated with materials that
can operate at higher temperatures or sustain higher fields. Proof of principle
has been established for the merit of Nb3Sn for SRF application. Research is
now needed to further exploit the material and reach its full potential with
novel deposition techniques. The third line of research is to push SRF
performance beyond the capabilities of the superconductors alone with
multilayered coatings. In parallel, developments are needed to provide quality
substrates, cooling schemes and cryomodule design tailored to thin film
cavities. Recent results in these three research thrusts suggest that SRF thin
film technologies are at the eve of a technological revolution. For them to
mature, active community support and sustained funding are needed to address
fundamental developments supporting material deposition techniques, surface and
RF research, technical challenges associated with scaling and
industrialization. With dedicated and sustained investment, next-generation
thin-film based cavities will become a reality with high performance and
efficiency, facilitating energy sustainable science while enabling higher
luminosity, and higher energy.
