a shell having distal and proximal ends;

a cathode structure disposed within the shell and having an electron emitting surface;

an anode physically coupled to the shell at the distal end and spaced a fixed distance from the emitting surface, the anode having an aperture for passage therethrough of a beam of electrons emitted by the emitting surface;

a plurality of leads adapted to apply a voltage to the cathode structure with respect to the anode sufficient to cause emission of the beam from the emitting surface;

a first insulator disposed within the shell proximal to the cathode structure, the first insulator having plural apertures having respective sizes in relation to corresponding ones of the plurality of leads such that the plurality of leads pass therethrough without contacting the first insulator, the first insulator providing stand-off for the voltage;

a second insulator disposed with the shell proximal from the first insulator, the second insulator having plural apertures permitting the plurality of leads to pass therethrough, the plurality of leads being tightly engaged within corresponding ones of the plural apertures of the second insulator to provide a vacuum barrier of the shell; and

a thermal choke coupled between the first insulator and second insulator to provide an indirect thermal path therebetween.