# Reflex klystron

1. Nov 12, 2014

### neeraj kaira

When the beam of electrons reflect back to the grid due to the repeller voltage in reflector plate ,how the grid decelerates the returning electrons ?? And how they release their energy to the grid ?

2. Nov 12, 2014

### davenn

hi there :)

Have a read of this explanation of the operation of a reflex Klystron

http://www.tpub.com/neets/book11/45d.htm

but quickly from the document to answer your 2 questions below .....

"The resonator potential also causes the resonant cavity to begin oscillating at its natural frequency when the tube is energized. These oscillations cause an electrostatic field across the grid gap of the cavity that changes direction at the frequency of the cavity. The changing electrostatic field affects the electrons in the beam as they pass through the grid gap. Some are accelerated and some are decelerated, depending upon the polarity of the electrostatic field as they pass through the gap. "

not released to the grid, but to the field around the grid.......

"When the grid field provides maximum deceleration, the returning electrons release maximum energy to the grid field which is in phase with cavity current. Thus, the returning electrons supply the regenerative feedback required to maintain cavity oscillations."

cheers
Dave

Last edited: Nov 12, 2014
3. Nov 12, 2014

### neeraj kaira

Some are accelerated and some are decelerated but how??? Plzz explain sir m totally confused :( :/

4. Nov 12, 2014

### neeraj kaira

According to this figure the grid provides maximum acceleration to the electrons when it is at positive peak...

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5. Nov 12, 2014

### neeraj kaira

now when the beam of electrons are repelled back to grid to suffer maximum deceleration so as to release their energy to the grid ...and according to figure the electrons reached the grid when it is at the same positive peak? How it is possible? In first time the grid provides acceleration to the electrons and in second time it provide deceleration...at the same positive voltage... :/

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6. Nov 13, 2014

### neeraj kaira

7. Nov 13, 2014

### dlgoff

8. Nov 15, 2014

### neeraj kaira

9. Nov 17, 2014

### sophiecentaur

You cannot demand rapid responses. If you get shirty / over demanding about it you will get none!

The slowing down and speeding up effect on the electrons is due to the voltages across the gap in the resonant cavity. At resonance, the initial bunches of electrons go out to the reflector and arrive back at the cavity in the right phase for their energy to be matched back into the cavity in 'impulses.
A normal two cavity klystron is easier to understand first, where you input a signal into one cavity and an amplified signal emerges from the output cavity. In a reflex klystron, one cavity does the job of two cavities, in effect.
The main thing to understand about the way a klystron works is that the electron beam is velocity modulated, initially and then, during the time in the drift space, the electrons become bunched in waves (density modulated). Energy from the KE of the input electron beam gets transformed into RF energy and amplification takes place.

10. Nov 17, 2014

### neeraj kaira

Thanku sir n last question please... How d K.E of electrons gets transformed to r.f energy?

11. Nov 17, 2014

### sophiecentaur

Have you looked up any Klystron theory? It's subtle. Imo, it's not the KE of the electrons that get transformed, it is the fact that they bunch together - producing a varying density of charge - which corresponds to electrical potential variations (at RF) across the gap in the cavity. If you let the electron beam go on for ever, the electron bunches will spread out again, resulting in velocity modulation again - and so on and so on. There is an optimum drift length for the Klystron to amplify.

12. Nov 17, 2014

### neeraj kaira

Ya i hv read multi cavity magnetron, klystron two cavity klystron reflex klystron but in my books it was not mentioned i even searchd on google but still not get that ...thatsy i asked..

13. Nov 17, 2014

### sophiecentaur

Too subtle for people to get involved with at that level, perhaps? It's quite amazing when you think that the efficiency can be over 50%, iirc.

14. Nov 17, 2014

### neeraj kaira

And sir i was hoping for a quick Reply not demanding i was just requesting... Bdw thanks a lot.
Good evening.

15. Nov 17, 2014

### sophiecentaur

It's an interesting topic an I'm impressed that you've been thinking so deeply about the Energy aspect.

16. Nov 17, 2014

### neeraj kaira

Ya sir m a electronics student n too much interested in microwave. N travelling wave tube is in my syllabus also :) thankuh so much

Last edited: Nov 17, 2014
17. Nov 17, 2014

### neeraj kaira

I asked this question to my teachers,friends n my senior's but unfortunately they r nt capable of answering dis

18. Nov 17, 2014

### sophiecentaur

By the way, the rules of PF do not permit people to post using 'text' spelling. It is considered bad form and many people will be reluctant to answer you if you use it. Try to stick to proper English - as a matter of courtesy.