Electron gun beam extraction with MOSFETs

Electron beams with an energy range of 10 keV at 2 A requiring intensity modulation with bandwidth from 50 kHz 7.5 MHz pose an interesting problem to the RF designer. Driving the extraction electrode of an electron gun can be a challenge with these requirements. The straight forward approach is the construction of a vacuum tube, single ended amplifier capable of delivering the anode voltage to the extraction electrode of the gun. However, vacuum tubes of this size and power are becoming increasingly expensive, and as the technology dies, the reliability of new components comes into question. The logical alternative is the implementation of solid state electronics. However, the 7.5 MHz 7 kV requirements pose a problem, as the solid state high voltage, high current technology does not exist in a single package. A new system of driving the extraction electrode of a Pierce type gun was developed using MOSFETs. Arranged in ultra-reliable “bricks” of series-parallel arrays, the MOSFETs allow for highly efficient amplification-mode operation. Amplitude linearity to 0.1% is achieved. The proposed system, capable of producing 7 kV at 25 kW will be implemented in the Electron Compressor experiment at Fermilab