Wu, Q. Belomestnykh, S.A. Ben-Zvi, I. Blaskiewicz, M. Hayes, T. Mernick, K. Severino, F. Smith, K.S. Zaltsman, A. JACoW Geneva, Switzerland 978-3-95450-178-6 10.18429/JACoW-SRF2015-WEBA07 English 982-986 WEBA07 cavity HOM operation damping SRF Contribution to a conference proceedings 2015 2015-12 http://dx.doi.org/10.18429/JACoW-SRF2015-WEBA07 http://srf2015.vrws.de/papers/weba07.pdf A 56 MHz superconducting RF cavity has been designed, fabricated and installed in the Relativistic Heavy Ion Collider (RHIC). The cavity operates at 4.4 K with a “quiet helium source” to isolate the cavity from environmental acoustic noise. The cavity is a beam driven quarter wave resonator. It is detuned and damped during injection and acceleration cycles and is brought to operation only at store energy. We have observed clear luminosity increase and bunch length reduction in the first operation of the cavity with Au + Au and Au + He3 collisions. The cavity voltage was limited by quenching in the Higher Order Mode coupler. This paper also discusses the cavity beam experiments with no higher order mode coupler in p + p and p + Au RHIC operation.