High Q cavities are an essential component for RF pulse compression. We are interested in developing compact superconducting cavities that operate at high temperature (liquid nitrogen, 80 K). We are designing an RF cavity at 11.424 GHz operating in the TM011 mode using eight facets with flat inner faces. These flat faces will be covered with High Temperature Superconductor (HTS) tapes. The cavity fill time (one exponential step) must be 1 microsecond. That sets loaded Q at 143,558. The external Q was selected to provide this loaded Q given the high ohmic Q. Cavity beta is 39.6. The cavity is fed by a TE10 to TM01 mode converter. Wall current is completely axial, so wall current does not cross the gaps between HTS tapes. Cavity tuning is accomplished by changing the separation between cavity facets using wedges.

SRF materials such as niobium have been extremely useful for accelerator technology but require low temperatures operation < 9 K. The development of high temperature superconductors (HTS) is promising due to their to their high critical temperature 89.5 K. This work intends to determine the high-power RF performance of such materials at X-band (11.424 GHz). Two kinds of REBCO coatings (thin film deposition and soldered tapes) on a copper substrate were tested. Testing was done in a hemispherical TE mode cavity due to its ability to maximize the magnetic field on the sample and minimize the electric field. We will report conductivity vs temperature at low and high power. We determine the quench field in the REBCO sample and explain the evidence which shows that the quenching is most likely due to reaching the critical current and not due to average applied heat load for powers up to 1.6 kW.