30-10-2012, 04:20 PM
A NEW TYPE OF MICROWAVE AMPLIFIERS BASED ON COLD SECONDARYEMISSION CATHODE
A NEW TYPE OF MICROWAVE.pdf (Size: 20.51 KB / Downloads: 33)
One of the promising application areas of field emitters is the development of microwave devices.
However field effect arrays supplying high current densities usually require ultra high
vacuum and are sensitive to discharges. Carbon films emitters are more robust but achievement
of current densities more than 1 A/cm2 is problematic. For this reasons it is interesting to
look for another types of cold emitters for high current applications. We consider the opportunity
to use secondary emission and single-electrode multipactor as the reliable cold source
of modulated electron beam which is less sensitive to surface interface, can supply high current
densities in technical vacuum and doesn’t require high electric fields or field amplification
(and any tip structure) [1]. This approach can make a basis for the development of a new
class of microwave devices (which we named alenotron) based on rf modulation of secondary
emission which doesn’t require magnetic focusing system, cathode heating, high power supply
voltage and can be considered as vacuum analogue of transistor.
In the considered design input rf signal and dc bias are applied to the gap in microwave cavity
(which is opened for dc current). One of the plates in the cavity represents a grid consisting of
material with high secondary emission yield. Electrons starting from the grid in the extracting
phase of rf field drift in the gap, are bunched, turn round in decelerating phase and return to
the grid after a period of rf voltage, i.e. in extracting phase again. Portion of them creates a
bunch of secondary electrons having increased total charge and “remembering” diminished
length of the primary bunch, and the rest of primary bunch penetrates through the grid in anode
gap where is accelerated and put out the rf power to a load. After several periods a short
dense bunch is formed in input gap having large charge. Single-electrode multipactor with dc
bias makes it possible to increase the gap at operation at high frequencies, so electron flow
fills the gap partially (as contrasted with double-electrode multipactor [2]).