Klystron unit

A klystron unit comprising:

• electron gun means for generating an electron beam along a beam path;
• collector means for collecting said electron beam;
• input resonator means located along said beam path in the vicinity of said gun, for defining an input resonance cavity and velocity-modulating said electron beam in response to an input signal;
• output resonator means for defining an output resonance cavity located along said beam path in the vicinity of said collector means, from which an output signal is picked up;
• at least one intermediate resonator means disposed along said electron beam path between said input and output resonator means, for defining at least one intermediate resonance cavity for velocity-modulating said electron beam;
• drift tubes disposed along said electron beam path, for coupling said resonators to each other and defining a drift gap in each resonance cavity;
• means for generating a magnetic flux along said electron beam path to focus said electron beam;
• and
• means for providing magnetic flux density distribution along said electron beam path to cause a maximum point of said distribution to fall within a predetermined area, and to cause said magnetic flux density to decrease from said maximum point to said collector means, said predetermined area being between said drift gap in said output resonance cavity and a point at most 3/5ths of the distance from said output resonance cavity drift gap to the drift gap of an intermediate resonance cavity which is adjacent to said output resonance cavity.