Tajima, T. Grumstrup, T.P. Ito, H. Kako, E. Okada, T. Sakai, H. Thompson, J.D. Umemori, K. JACoW Publishing Geneva, Switzerland 2673-5504 978-3-95450-234-9 10.18429/JACoW-SRF2023-TUPTB018 English 425-428 cavity SRF controls experiment vacuum Contribution to a conference proceedings 2023 2023-09 https://doi.org/10.18429/JACoW-SRF2023-TUPTB018 https://jacow.org/srf2023/papers/tuptb018.pdf We have started parameter optimization for the coating of MgB₂ using a 1-cell 1.3-GHz elliptical cavity with holes for small samples. Our coating method is based on a 2-step technique, i.e., coat a B layer by flowing diborane gas in the first step and react it with Mg vapor in the 2nd step. Three 6 mm x 6 mm B-coated flat samples are attached at inlet, outlet beam pipes, and at a cell equator and reacted with Mg vapor with different parameters and conditions. We started to see the superconducting transitions on samples but Tc is still lower than our goal of >35 K. We will present our current status of B-Mg reaction tests and construction of B coating system.