  A 56 MHz superconducting RF cavity was designed and installed in the
Relativistic Heavy Ion Collider (RHIC). It is the first superconducting quarter
wave resonator (QWR) operating in a high-energy storage ring. We discuss herein
the cavity operation with Au+Au collisions, and with asymmetrical Au+He3
collisions. The cavity is a storage cavity, meaning that it becomes active only
at the energy of experiment, after the acceleration cycle is completed. With
the cavity at 300 kV, an improvement in luminosity was detected from direct
measurements, and the bunch length has been reduced. The uniqueness of the QWR
demands an innovative design of the higher order mode dampers with high-pass
filters, and a distinctive fundamental mode damper that enables the cavity to
be bypassed during the acceleration stage.
