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Author Topic: How does a magnetron work?  (Read 23325 times)

Offline chris

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How does a magnetron work?
« on: 27/11/2008 21:00:06 »
How does the magnetron in a microwave generate the waves that ultimately cook my dinner?

Chris


 

lyner

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How does a magnetron work?
« Reply #1 on: 28/11/2008 11:56:45 »
The Magnetron is a great 'quick and dirty' way to produce a lot of microwave energy from the energy in an electron beam.

It's one of a class of 'velocity modulated' tubes, which includes Klystrons and Traveling Wave Tubes. You start off with a beam of electrons with a lot of DC energy, all at the same speed (as in a TV tube) and then you speed up some and slow down others (velocity modulate). The result is that you eventually get 'bunching' of the electrons  (density modulation) like cars on a motorway. These peaks and troughs represent AC energy which you can extract from the beam.

First, a simple case: In a Klystron, which is an amplifier, you pass the beam through a gap in a resonant cavity (resonates at the frequency of the input RF you want to amplify). The volts across the gap vary as the input RF signal varies and alternately speed up and slow down the electrons passing through. There is then a 'drift space' in which the bunching occurs. The beam then passes through a second cavity which resonates at the same frequency and couples the RF energy out. You can get 100 times the amount of RF energy out of the electron beam as the RF energy you put in. A Klystron is not too efficient, though but is a 'good quality' amplifier.

The Magnetron does the same sort of thing - fast electrons are made to go in a circular path in a strong magnetic field. They go past a set of resonant cavities which select / amplify any small, natural, amount of bunching, at the appropriate frequency until there is a lot of RF energy in the beam. The RF energy is taken out via one of the cavities and the electrons run into the Anode and dissipate the DC energy. All oscillators are based on this principle: effectively amplifying at one frequency until the system starts to oscillate at that frequency.

The Magnetron output signal is not a 'good quality' signal but is ideal for Heating and Radar pulses, where high power is important.
See http://www.radartutorial.eu/08.transmitters/tx08.en.html for some good pictures and a longer, more accurate description.
« Last Edit: 28/11/2008 12:48:08 by sophiecentaur »
 

Offline erickejah

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How does a magnetron work?
« Reply #2 on: 28/11/2008 21:05:27 »
quite interesting, :o :o :D
 

lyner

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How does a magnetron work?
« Reply #3 on: 29/11/2008 00:00:48 »
Why thank you young man. ;)
 

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How does a magnetron work?
« Reply #3 on: 29/11/2008 00:00:48 »

 

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