Microwave tube with photoinjector cathode, photoelectric tube

[Salvador12]

For a while there have existed photocathodes/photoinjectors aka photoelectric electron gun. So instead of thermionic emission or cold cathode field emission the emission happens via the photoelectric effect.

I do wonder have they been used or attempted in RF amplifier devices such as klystrons? The way I see it is this, in a klystron or other known vacuum RF tubes you have a thermionic cathode emitting constant electron beam which then gets as in klystron velocity modulated within the signal cavity and then the beam gets bunched and induces power in output cavity.
But with a photocathode that is controlled by a laser for example one could simply modulate the electron beam with the light that shines onto it.
So in theory you could omit the first cavity and the bunching and simply have a DC acceleration field like you do already and achieve the electron modulation via the cathode current modulation which is achieved by applying the RF signal to the laser control.
Is there anything on the market like that?
https://dspace.mit.edu/bitstream/handle/1721.1/95319/97ja001_full.pdf;sequence=1

In a paper like this they used the photoinjector cathode but applied a RF field made by a klystron to accelerate the electrons.

I do wonder whether a system can be made where a cavity is not needed at all. You simply have a photocathode and an accelerating field and an anode. You then modulate the cathode however you wish and you end up with a RF current in the anode terminal which you can then couple directly to a RF transformer or balun etc?

 

[betwixt]

The problem I see in that idea is that modulating the emission doesn't change the velocity, only the quantity. There is no 'bunching' mechanism to squeeze or expand the light beam like you can do with electrical or magnetic fields in klystrons or TWT devices. I'm no expert in this topic, maybe others have better knowledge.

Brian.

 

[Salvador12]

The problem I see in that idea is that modulating the emission doesn't change the velocity, only the quantity. There is no 'bunching' mechanism to squeeze or expand the light beam like you can do with electrical or magnetic fields in klystrons or TWT devices. I'm no expert in this topic, maybe others have better knowledge.

Brian.

Yes without any input cavity after the photoinjector you could not velocity modulate the beam if one uses a static DC accelerating field but why would you need to velocity modulate the beam? A klystron needs that because it operates with a static DC electron beam, but here you already modulate the beam with the varying current within the photoinjector.