a radio frequency coaxial vacuum feedthrough is provided which utilizes a cylindrical ceramic vacuum break formed of an alumina ceramic . the cylinder is coaxially disposed and brazed between tapered coaxial conductors to form a vacuum sealed connection between a pressurized upstream coaxial transmission line and a utilization device located within a vacuum container . the feedthrough provides 50 ohm matched impedance rf feedthrough up to about 500 mhz at power levels in the multimegawatt range .