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johnm214


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Physics Help Requested- Understanding a Cavity Magnetron
#14985627 - 08/27/11 07:26 AM (12 years, 8 months ago) |
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Hi guys, found something in wikipedia that didn't make any sense, and decided to see what you bright folks have to say!
Anyways, i was reading the article on the cavity magnetron, related to some other things I was interested in, but am unable to fathom how this thing works from their description or diagram.
Specifically, here is what they say and what the diagram shows:
Quote:
All cavity magnetrons consist of a hot cathode with a high (continuous or pulsed) negative potential by a high-voltage, direct-current power supply. The cathode is built into the center of an evacuated, lobed, circular chamber. A magnetic field parallel to the filament is imposed by a permanent magnet. The magnetic field causes the electrons, attracted to the (relatively) positive outer part of the chamber, to spiral outward in a circular path rather than moving directly to this anode. Spaced around the rim of the chamber are cylindrical cavities. The cavities are open along their length and connect the common cavity space. As electrons sweep past these openings, they induce a resonant, high-frequency radio field in the cavity, which in turn causes the electrons to bunch into groups. A portion of this field is extracted with a short antenna that is connected to a waveguide (a metal tube usually of rectangular cross section). The waveguide directs the extracted RF energy to the load, which may be a cooking chamber in a microwave oven or a high-gain antenna in the case of radar.

http://en.wikipedia.org/wiki/Cavity_magnetron
Basically, I can imagine this thing resonating with an appropriate power source already at the desired frequency that matches the geometry of the annode, however, the article says specifically that the cathode can work with either a continuous or pulsed DC power supply, so what is causing the microwave signal being outputted?
The way I figure it, with a continuous DC current, then the electrons are sweeping past the cavities continuously, right? So how could there be any sort of resonating field induced if the current isn't periodic?
Does this make any sense to anyone else?
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DieCommie

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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: johnm214]
#14986482 - 08/27/11 12:06 PM (12 years, 8 months ago) |
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Hmm... Im not sure. I've never looked at one of these before. Note that the B field is causing the electrons to circle around the cathode. The centripetal acceleration of these electrons will produce radiation of a particular frequency. This is the radiation that I believe they are tapping into with waveguides.
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johnm214


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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: DieCommie]
#14986531 - 08/27/11 12:15 PM (12 years, 8 months ago) |
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I get that the parrallel (with the cathode) magnetic field would cause a spiraling that would make the electron's trajectory deflect angularly as it moves to the annode, but with a constant curremt, where are you getting the oscillation from that produces the microwaves, or any EM radiation? Looks to me like with a constant current/voltage input from your constant DC input you'd just get a constant induced magnetic field that wouldn't be useful whatsoever.
See what I mean? Where does the oscillating field come from if the current flowing from that cathode to the anode is roughly constant over time?
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DieCommie

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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: johnm214]
#14986560 - 08/27/11 12:23 PM (12 years, 8 months ago) |
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Radiation is an oscillating field. Anytime a charge accelerates, it produces an oscillating field. Since the charge is accelerating (in a centripetal way) then it is producing an oscillating (EM) field. Its not the direct current that is making the radiation, its the accelerating electrons.
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johnm214


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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: DieCommie]
#14986682 - 08/27/11 12:50 PM (12 years, 8 months ago) |
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Given that these charges are large in number and moving in a radially symetric path, what would by the net magentic field? Doesn't seem like it would be changing over time, so you'd have a magnetic field that isn't moving going through a hunk of metal (the annode) which isn't moving, and it doesn't seem like any kind of signal is going to be induced.
I could understand what your saying if this put through one electron at a time, but since the flow of electrons is constant over time and radially symetric, the net field wouldn't seem to move any more than the electrons moving through a wire cause the magnetic field surrounding the wire to move. In both cases the charges are radially distributed and so numerous that the average field is static.
So how does this apparently static field and unmoving hunk of metal and vacuum produce microwaves?
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DieCommie

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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: johnm214]
#14986729 - 08/27/11 01:00 PM (12 years, 8 months ago) |
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Quote:
I could understand what your saying if this put through one electron at a time, but since the flow of electrons is constant over time and radially symetric, the net field wouldn't seem to move any more than the electrons moving through a wire cause the magnetic field surrounding the wire to move.
Why would it seem that way?
Accelerating charges produce EM waves. They can be accelerating in a linear fashion, slowly and constantly and they will produce EM waves. They can be accelerating in a centripetal fashion, constantly and symmetrically, and they will produce EM waves. If you accelerate a lot of them, then you increase the intensity of the EM waves they are putting off.
Change the radius, the speed or the charge on the particle and you can get EM waves of any frequency you want.
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DieCommie

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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: DieCommie]
#14986766 - 08/27/11 01:09 PM (12 years, 8 months ago) |
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Edited by DieCommie (08/27/11 01:17 PM)
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Stonehenge
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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: DieCommie]
#14987085 - 08/27/11 02:11 PM (12 years, 8 months ago) |
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My take on it is the cavities are a type of tuned circuit. The frequency tuned to will depend on the size and shape of the cavity. The electrons moving in a spiral contain within them electromagnetic energy. The spiraling electrons entering the cavities is like stroking a tuning fork of a certain size and shape. The force applied to the tuning fork is totally unlike the sound waves produced since the striiking or stroking of the fork merely gives energy into the system. The system of the fork then converts the energy in it into the frequency it's tuned to.
Same idea with the magnetron or cavitron. The spiraling electrons add energy to the cavities which in turn use it to produce their resonant frequency. It is somewhat analogous to a conventional electric tuned circuit formed by an inductor and capacitor. The spiraling electons are going to emit radiation, as dc said and this is converted into the desired wavelength by the characteristics of the cavities.
-------------------- “A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
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johnm214


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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: Stonehenge]
#14989836 - 08/28/11 04:20 AM (12 years, 8 months ago) |
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Quote:
DieCommie said:
Quote:
I could understand what your saying if this put through one electron at a time, but since the flow of electrons is constant over time and radially symetric, the net field wouldn't seem to move any more than the electrons moving through a wire cause the magnetic field surrounding the wire to move.
Why would it seem that way?
Accelerating charges produce EM waves. They can be accelerating in a linear fashion, slowly and constantly and they will produce EM waves. They can be accelerating in a centripetal fashion, constantly and symmetrically, and they will produce EM waves. If you accelerate a lot of them, then you increase the intensity of the EM waves they are putting off.
But what field do these waves create and why? Seems to me that the radially symetric current from the two electrodes would produce a radially symetric magnetic field.
If there were one charge, for example, the magnetic field would change with time as the electron moves about. If there are many electrons, however, with a current that is not time dependant, then the electrons will be distributed radially symetrically about the cathode and will constantly be moving between the cathode and anode. The summation of the individual charges should produce a uniform magnetic field that does not change with time, to my understanding, as the distribution and velocity of the charges in the apparatus does not change with time, only the individual charge carriers. As such, an induced resonance between the cavities by the first electron to pass by would be altered by the second and subsequent electrons, as the current and voltage is constant. As a result, every conceivable phase would exist and the net product would be no resonance.
Please explain what the mechanism of microwave production is as far as you can tell?
Quote:
Change the radius, the speed or the charge on the particle and you can get EM waves of any frequency you want.
How? Do you disagree the megnetic field created by the flow of electrons between the two electrodes does not change over time and hence the electrons in the anode would not move over time in response to said field? What is producing the microwaves then with this static magnetic field, static electric field, and with no moving conductors?
Quote:
Stonehenge said: My take on it is the cavities are a type of tuned circuit. The frequency tuned to will depend on the size and shape of the cavity. The electrons moving in a spiral contain within them electromagnetic energy. The spiraling electrons entering the cavities is like stroking a tuning fork of a certain size and shape.
Yes, but with a constant current/voltage, what is "plucking" the tuning fork (annode block)?
If you exert a contant force on a tuning fork it does not vibrate. You must exert a changing force, such as the application of force followed by the removal of that force, and then you produce the charecteristic movement which produces the sound.
Likewise, with a constant net magnetic field and no net motion (no motion at all) of any conductor, what is creating the oscillating field, the microwaves?
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Seuss
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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: johnm214]
#14989850 - 08/28/11 04:42 AM (12 years, 8 months ago) |
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> What is producing the microwaves then with this static magnetic field, static electric field, and with no moving conductors?
The electrons spinning inside the central cavity of the magnetron form a pattern that looks like a bicycle wheel with a bunch of (spinning) spokes. (This is called a rotating space charge wheel.) When one of the "spokes" approaches an anode vane (the walls between the anode cavities) a positive charge is induced within the vane. As the electron spoke movies on, the positive charge diminishes in the first vane and forms in the next vane. Current is induced because the physical structure of the anode forms the equivalent of a series of high-Q resonant inductive-capacitive (LC) circuits. The walls of the cavity form the inductor and the gap at the entrance of the cavity form the capacitor.
I think the part you were missing is the rotating cloud of electrons is not a 'equal density' cloud, but instead is shaped like a gear with very long teeth (or a bike wheel with spokes).
-------------------- Just another spore in the wind.
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trendal
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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: johnm214]
#14990097 - 08/28/11 08:02 AM (12 years, 8 months ago) |
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--------------------
Once, men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them.
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trendal
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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: Seuss]
#14990102 - 08/28/11 08:03 AM (12 years, 8 months ago) |
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Quote:
Seuss said: I think the part you were missing is the rotating cloud of electrons is not a 'equal density' cloud, but instead is shaped like a gear with very long teeth (or a bike wheel with spokes).
Like this:
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Once, men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them.
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Stonehenge
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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: trendal]
#14991270 - 08/28/11 12:50 PM (12 years, 8 months ago) |
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Seuss gave a good explanation but one which may be hard to visualize. The setup with the magnet and dc current flow is designed to produce turbulence as the electric current attempts to complete the circuit by reaching the anode. When the electrons enter the cavities, there are various effects at work. The flow of electrons tends to spread out as it enters and will strike the anode at different times. Since the electrons are not free to travel directly but are subject to a magnetic field, this tends to cause spiraling in the electrons trajectory.
We have this turbulent electron flow which would tend to produce radio frequency noise or a mixture of frequencies. Since the cavities are designed to resonate at a certain frequency, that frequency is maintained. You could call the turbulent electron flow the force striking the tuning fork. If you put a 60 cycle hum into a fork, it will instead resonate at the frequency it is designed for.
Another way to visualize it is blowing air across the rim of a bottle. The turbulent air molecules provide energy and the size and shape of the bottle determines what frequency it will resonate at. A large bottle having a low frequency and vice versa for a small one.
The rf energy that enters the cavities will bounce off the walls of the cavity and either form a standing wave or be canceled out. The radius of the cavity will correspond to the frequency of the wave. The wavelength that corresponds to the radius is reinforced and other frequencies tend to die out. If left on it's own the magnetron will reach a steady state and current flow will be limited. By siphoning off part of the signal, more energy must be put into it to return it to the steady state. A waveguide is used rather than copper wire because at these high frequencies, the current does not flow well in a wire. The inductance of even an inch of straight wire is enough to make a difference. The waveguide does just what its name says, it allows the radiation to travel the length of it by bouncing off the walls until it reaches the load.
-------------------- “A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
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Seuss
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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: Stonehenge]
#14991583 - 08/28/11 01:52 PM (12 years, 8 months ago) |
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Quote:
Stonehenge said: The setup with the magnet and dc current flow is designed to produce turbulence as the electric current attempts to complete the circuit by reaching the anode. When the electrons enter the cavities, there are various effects at work. The flow of electrons tends to spread out as it enters and will strike the anode at different times. Since the electrons are not free to travel directly but are subject to a magnetic field, this tends to cause spiraling in the electrons trajectory.
Huh? The electrons mostly stay in the rotating space charge wheel around the cathode. The electrons that leave the rotating space charge wheel end up on the anode vanes, not within the anode cavities. Current is induced within the anode (around the cavities) which creates a B-field normal to the cavity. The size and shape of the cavity determine the LC characteristics which results in the tuned RF. F_resonance=(1/2pi)*sqrt(1/LC). The gap between anode vanes determines C and the size of the cavity determines L.
Quote:
We have this turbulent electron flow which would tend to produce radio frequency noise or a mixture of frequencies. Since the cavities are designed to resonate at a certain frequency, that frequency is maintained. You could call the turbulent electron flow the force striking the tuning fork. If you put a 60 cycle hum into a fork, it will instead resonate at the frequency it is designed for.
Uh, no. The passage of the "spokes" of the electrons that are spinning around the cathode are acting as the "pluck". The size and shape of the anode cavities determine the frequency. Again, it is not the electrons entering the anode cavities, but the induced charge within the walls that make up the anode cavities. It is the oscillation of the induced charge within the anode cavity walls that results in radiated RF. The electrons from the cathode simply provide energy that drives the oscillation.
Quote:
Another way to visualize it is blowing air across the rim of a bottle. The turbulent air molecules provide energy and the size and shape of the bottle determines what frequency it will resonate at. A large bottle having a low frequency and vice versa for a small one.
I've seen this analogy used before, but it is not very good.
To be fair, this is a very difficult subject. It was part of my waves and fields EE class which wasn't taught until your junior/senior year after you had taken a lot of physics and calculus.
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Stonehenge
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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: Seuss]
#14991921 - 08/28/11 03:09 PM (12 years, 8 months ago) |
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Seuss, with all due respect i think you are getting too caught up in one model of action.
>Huh? The electrons mostly stay in the rotating space charge wheel around the cathode.
The electrons must flow or else you do not have power input. On their journey to the anode they go through contortions which produce the rf energy you want.
>The electrons that leave the rotating space charge wheel end up on the anode vanes, not within the anode cavities.
Much of the flow will go there, sure. So what? Some electrons will enter the cavities and end their journey by hitting the anode and completing the circuit.
>Current is induced within the anode (around the cavities) which creates a B-field normal to the cavity.
What do you mean "induced"? It's a normal current flow, not electromagnetic induction which produces a current in the anode. Or i may be reading you wrong. There will be some of that going on sure, since we have rf being produced but the power comes from the flow of electrons completing the circuit and giving up energy along the way.
>The size and shape of the cavity determine the LC characteristics which results in the tuned RF. F_resonance
I agree with the size and shape part but looking at it as simply an inductor and capacitor is missing a large part of the picture, imho. Much like the way the output radiation bounces off the inside of the wave guide, the radiation bounces off the walls of the cavity and forms standing waves. Otherwise, you would just simply use an inductor and capacitor in a conventional circuit. I'm not saying this does not go on, yes there is inductance in the anode and capacitance between the anode and cathode. There is also capacitance between parts of the anode.
>The gap between anode vanes determines C and the size of the cavity determines L.
I think you are overthinking it and overlooking the obvious. Tell me this, what is the relationship between cavity size and frequency output?
You seem to not like my analogies and i never said they were an exact analogy. However they serve to illustrate parts of the principles involved.
>Uh, no. The passage of the "spokes" of the electrons that are spinning around the cathode are acting as the "pluck".
Isn't this another way of putting what i said? I spoke of electron turbulence and you speak of passage of spokes. Spokes themselves are analogies and will fail to always predict the action. Obviously we are not blowing air across the cavity openings. This was an analogy. What i'm saying is that the cavities tune for a certain frequency and this is not just a matter of l and c but of the radius of the cavity. The radiation is absorbed by the walls and reemitted. You did say something like that when you said it was induced. This is very much like the way a wave guide works. I think my analogy of a bottle and the sound produced is close, you don't like it much.
I think a large part of the conflict here is a conflict of analogies rather than actual theory.
-------------------- “A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
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johnm214


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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: Seuss]
#14992129 - 08/28/11 03:49 PM (12 years, 8 months ago) |
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Thanks for the help everyone.
Quote:
I think the part you were missing is the rotating cloud of electrons is not a 'equal density' cloud, but instead is shaped like a gear with very long teeth (or a bike wheel with spokes).
Yeah, definitely, that makes sense as the induced current would change directions over time and thus there would be some mechanism to induce this desired frequency in the anode.
What I'm unsure of is why is this 'rotating' wheel of charge forming?
What I'm imagining now is that as the device is turned on: any miniscule fluctuation in the current flow will tend to be affected by the geometry (capacitance and inductance) of the vanes/cavities and reinforce that aspect of the fluctuation compatible with the resonant frequency and resist that aspect incompatible. This would then produce a growing ac current in the anode block that oscillates at the 'tuned' frequency of the circuit. Then I would imagine the alternating relative potential in the anode vanes would cause the electrons between the two electrodes to repel/attract at various vanes and thus the spoke wheel is formed, which "rotates" due to the alternating relative potentials of the vanes.
Is this reasonable/correct? If so I can see I neglected the anode's effect on the current between the electrodes and the fact that any resonance would shape the path of the electrons.
I hope that's right, anyways 
Can someone explain what is creating the inductance and how you'd design that part of the device?
(btw, anybody know why things with transparent backgrounds and thin lines, like the graphic trendal posted, look fine against a white background but terrible against the default shroomery background in my Firefox browser, an "aliasing-like" effect"?)
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Seuss
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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: johnm214]
#14992790 - 08/28/11 06:04 PM (12 years, 8 months ago) |
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Quote:
What I'm imagining now is that as the device is turned on: any miniscule fluctuation in the current flow will tend to be affected by the geometry (capacitance and inductance) of the vanes/cavities and reinforce that aspect of the fluctuation compatible with the resonant frequency and resist that aspect incompatible. This would then produce a growing ac current in the anode block that oscillates at the 'tuned' frequency of the circuit. Then I would imagine the alternating relative potential in the anode vanes would cause the electrons between the two electrodes to repel/attract at various vanes and thus the spoke wheel is formed, which "rotates" due to the alternating relative potentials of the vanes.
I believe that is all correct, except the very last bit (in italics). The system has both a DC field that extends from adjacent anode vanes to the cathode and an AC field that extends between adjacent vanes. The electrons which travel toward the positive anode vanes gain a higher tangential speed while the electrons which travel toward the negative vanes slow down. (Remember, the vanes will oscillate between positive and negative.)
Now add in the permanent magnets above and below which create an axial magnetic field that is perpendicular to the initial direction of the electrons. As the electrons accelerate away from the cathode towards the anode, the axial magnetic field causes them to turn. The faster electrons will experience a higher magnetic field, creating a sharper turn, and end up returning to the cathode. The slower electrons will accelerate towards the anode forming the spoke pattern. When an electron eventually makes it to the anode vane, it dissipates its energy into the vane, thus the system doesn't remain static.
(It has been a while; I think I got that correct. Somebody with a fresher mind might want to double check.)
Edit: Actually, rereading what you wrote, I believe you are correct... I just went into more detail about what happens.
-------------------- Just another spore in the wind.
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Stonehenge
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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: Seuss]
#14992939 - 08/28/11 06:29 PM (12 years, 8 months ago) |
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If you say so seuss then it must be so. However i noticed that you avoided my questions. Just answer me this, is there a relationship between the radius of the cavity and the frequency of the output? If so, what is that relationship?
-------------------- “A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
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Seuss
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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: Stonehenge]
#14993565 - 08/28/11 08:48 PM (12 years, 8 months ago) |
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> If you say so seuss then it must be so.
*yawn*
> Is there a relationship between the radius of the cavity and the frequency of the output? If so, what is that relationship?
The resonant frequency is determined by the LC (inductance-capacitance) of the cavity. In layman terms it would be acceptable to say that the cavity size (not radius) determines the resonant frequency. However, this is a gross simplification of what is really happening and ignores several import aspects. In electrical engineering terms it is the inductance-capacitance of the cavity that determines the resonant frequency. I gave the relationship previously. As far as I know, there is no relationship that directly relates cavity size to resonant frequency because cavity size does not tell us what the inductance and capacitance are. What matters is F_res ~ 1/(2*pi*sqrt(LC)) where L is (more or less) determined by the size of the cavity and C is (more or less) determined by the size of the slot.
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Stonehenge
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Re: Physics Help Requested- Understanding a Cavity Magnetron [Re: Seuss]
#14996214 - 08/29/11 12:00 PM (12 years, 8 months ago) |
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I should have explained better what a wave guide (wg) is. Some of those following this thread might be in the dark and not want to google it. Basically a wg is a pipe made out of metal. They are usually square or rectangular in cross section though other shapes are possible. What happens is the signal comes out as radiation and bounces along the inside of the pipe. When it hits a wall it is reflected back with little loss. I think the wall acts as a sort of antenna which absorbs the signal and then sends it back out. You could think of it as being like light which hits a mirror and is reflected. Light itself is high frequency radiation. I'm not sure anyone knows exactly what happens when light hits a reflective surface. I'm not sure if the molecules absorb and retransmit the light or what is going on.
A good analogy of a wg is a fiber optic system. In that, the light bounces along a fiber much like the way a signal bounces along inside a wg.
Thank you for your analysis of that system, seuss. I do have some other ideas but i'm sure what you say has validity. I wonder though if all we are talking about is what analogy best fits. The wg has inductance and capacitance too. But we usually speak of the beam being reflected. You don't like the idea of the waves being reflected in the cavity and prefer to speak of l and c.
However, if we used the analogy of reflection in the cavities, then each cavity would tend to tune for a wavelength of around 2 x radius or wl = diameter. What i'm thinking could go on, and feel free to shoot this idea down everyone, is that the radiation going into the cavity hits one side, is reflected like being in a room full of mirrors, goes to the center as a focal point and then on to the other side.
The center of the cavity would correspond to the zero point on a conventional wave graph. As it spreads out and hits one side, it reaches a peak, is reflected back and hits zero again at the center focal point, goes then to a negative peak at the opposite wall, is reflected back to the zero point and starts over.
So we have a series of cavities tuned to the same frequency with one opening. Through the opening comes the slightly tuned rf which is then fine tuned to the desired wavelength. The signal then comes out the same door and goes into the central area where the cathode is. There would be some losses but without drawing off the signal you would tend to reach a steady state with standing waves, i would think.
This does not ignore nor deny the l and c nature of the cavities and other parts. You say it works on l and c, i say sure but it acts like a reflection. If the radiation was absorbed by the anode you would have a dampening off situation and there would not be enough regeneration to have meaningful output.
-------------------- “A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835) Trade list http://www.shroomery.org/forums/showflat.php/Number/18047755
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