My explaination of Direct Conversion

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mattman
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Joined: Tue May 27, 2008 11:14 pm

My explaination of Direct Conversion

Post by mattman »

Direct conversion is sticking charged particle to surfaces that they hate.

The goal is to get the ion to stick to a positive surface. They hate this.

However, they are coming from a high velocity beam. Their momentum drives them into the metal anode anyway.

This fresh supply of positive charge keeps the anode positive.

The fresh supply of electrons keeps the cathode negative.

This maintains a voltage drop and drives current.

That is how energy might be captured from alpha particles from a fusion reactor.

D Tibbets
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Re: My explaination of Direct Conversion

Post by D Tibbets »

I don't think so...

Any time a high speed high KE charged particle hits an electrode, they transfer their energy to the electrode , mostly as heat. It is the same process as a rock hitting a wall.

Direct conversion can work in both directions. The potential can accelerate of decelerate a charged particle. It depends on the arrangement.
If a charged particle is near an electrode of opposite or like charge it is accelerated or decelerated accordingly. This represents a change in the KE or speed of the charged particle, and the direct transfer of energy to, or from the particle and from, or to the electrode.
But, once the charged particle touches the electrode, it is stopped, it's KE is converted to heat. This heat can make electricity by heating water and driving a steam turbine, or other heat engine like a Sterling engine or thermocouple, but these methods are only efficient up to ~ 30-40% for converting to electricity. This is why you need water cooling towers, etc at power plants, the remaining heat is waste and needs to be dissipated, otherwise the entire apparatus will eventually reach the same temperature (or melt) and it is the temperature difference that drives these heat engines.

Direct conversion is different. There is no thermal/ heat intermediary. Theoretically, conversion to useful electricity could approach 100%. Practically it is closer to ~ 80-90% efficiency due to resistance in wires, inefficiencies in transformers, compromises, etc.

For direct conversion you may arrange things so that a positive ion with a KE of eg: 1,000,001 eV passes (not hitting) electrodes with a - 100,000 voltage, Each electrode absorbes 100,000 eV of energy of the ion,the last electrodes (10 in series) leaves the ion with a residual KE of 1 eV. The ion is then allowed to hit the vacuum vessel wall or other grounded surface. This residual energy is converted to heat, but because the heat is much less the thermal load on the structure is much less, and only mild if any active cooling is required. This is an ideal example, in practice things would not be so clean.

How do you prevent the high energy ions from hitting the electrodes? It is all a game of magnetic shielding, and consideration of the vectors (direction of travel) of the ions. Gauss Law considerations are essential to direct conversion (exceptions?).

Think of ion rocket engines, electron guns, particle accelerators, Magrid recirculation, etc. They all work by direct conversion of voltage potential energy into KE of a free charged particle (or visa versa). Creation of the free charged particle in the first place is a different topic.

Dan Tibbets
To error is human... and I'm very human.

mattman
Posts: 459
Joined: Tue May 27, 2008 11:14 pm

Re: My explaination of Direct Conversion

Post by mattman »

Dan,

Here is what I thought direct conversion was…

Image

This would also work for the (+). Based on what you said,

Image

I still do not understand how the energy gets from the ion to the electrodes.

I guess I can reason this out. If you see the process in reverse: the field from the electrodes pushing the ion forward.

hanelyp
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Re: My explaination of Direct Conversion

Post by hanelyp »

When an ion moves with an electric potential field, it absorbs energy (and voltage) from the field. When the ion moves against the field, it adds energy to the field. The field removes/adds energy to the electrodes it is between, said electrodes acting as capacitor plates.

From another perspective, moving charge between plates of a charged capacitor adds or removes energy from the capacitor.

For simple direct conversion you just need 2 electrodes for an ion to travel between. In a polywell it's a little more complex with:
- the fusion plasma serving as the ion emitter,
- the magrid as a vacuum tube grid, (ions below an energy threshold are reflected)
- a grid surrounding the magrid to reflect electrons that escape from the wiffleball, (electrons up scattered enough pass, degrading direct conversion)
- finally the collector electrode(s).

With additional electrodes you can sort ions based on energy into bins, collecting each bin into a collector matching the low energy bound of that group.
The daylight is uncomfortably bright for eyes so long in the dark.

mattman
Posts: 459
Joined: Tue May 27, 2008 11:14 pm

Re: My explaination of Direct Conversion

Post by mattman »

Ok, I can see that.


Still, what would be wrong with the scenario described above?

D Tibbets
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Re: My explaination of Direct Conversion

Post by D Tibbets »

mattman wrote:Ok, I can see that.


Still, what would be wrong with the scenario described above?
Your second drawing matches what I said. But, you seem to have difficulty seeing the transferr of energy without physical contact. The accelerator perspective is usefull to demonstrate that this happens. A cathode ray TV accelerates electrons by attracting towards and past a positively charged electrode. The electron gains energy without actually touching the electrode. It is the electromagnetic field surrounding the electrode that is the intermediary. The field is maintained by the potential of the electrode but it is not only present at the surface of the electrode. It permeates space and weakens via the inverse square law, and it can be effectively be shielded by Gauss Law considerations . The charged particle is free to move and is accelerated accordingly, always directly towards or away from the electrode. But the initial vector of the particle may make it fly past the electrode before it actually hits the electrode, and having two electrodes with one on either side results in the accelerating vector being between them. The vectors are summed. Also magnetic shielding may impede flight directly towards the electrode.

The bins mentioned are important in the sense of removing the charged particles from the system. They are not where the energy transfer is occurring though, provided your direct energy conversion scheme is working. The bins collect the particles so that they cannot subsequently be re accelerated by subsequent electrodes or build up harmful Coulomb charges. That would defeat the purpose of the converter. The arrangement of electrodes, magnetic shielding, and Gauss Law considerations allows for this staged process.

A single stage of a positive electrode decelerating the ion as it approaches would convert some or almost all of the KE of the ion to potential in the electrode. Gauss Law helps and confounds the system, but this simple example illustrates the process. Perhaps you are laboring under the conversion of this KE to potential energy conversion driving electrical current in the wire connected to the electrode. If an ion with KE strikes the electrode, the KE is converted to heat, this heat can generate steam and this steam can drive a dynamo to make electricity. This is straight forward. The potential (note that potential energy and potential=voltage are equivalent) of the electrode also generates electricity if it is connect through a load to ground. With a voltage, curren will flow through a wire, but if the voltage is not maintained by the input of energy, the voltage will quickly drop to zero and current will stop. The direct conversion of the KE of the ion, through the electromagnetic field generated by the electrode continuously feeds energy into the electrode so the voltage is maintained despite perhaps huge current flow towards ground through the wire connected to the electrode. The dynamo is doing the same thing, except it has an intermediate step of the mechanical spinning of the generator. The voltage is maintained despite the current drain into the electrical grid. The use of direct conversion is just, um... more direct.

The KE of the ion is converted to potential energy in the electrode, and this potential energy = potential or voltage. So long as this potential energy is maintained the voltage will be maintained despite the appropriate current flow to ground (and back into the electrode as the electrons in the wires are cycling back into the opposite end of the electrode). In this situation if the electrode is not connected to ground (no current flow) it is floating and will soon reach an equilibrium with a voltage equivalent to the KE of the ions. This would result in conditions perhaps useless and unsustainable, or might be utilized in a manner that I think Bussard mentioned in the patent application.

Dan Tibbets
To error is human... and I'm very human.

KitemanSA
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Re: My explaination of Direct Conversion

Post by KitemanSA »

Mattman,
Answers to most of your technical questions can be found here: http://www.askmar.com/Fusion.html

Specifically, check out this one. http://www.askmar.com/Fusion_files/Venetian%20Blind.pdf

mattman
Posts: 459
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Re: My explaination of Direct Conversion

Post by mattman »

I reworked this explanation, Tell me what you think:


Direct Conversion:

Direct conversion uses a charged particles’ motion to make a voltage. This voltage drives electricity in a wire. This becomes the electrical power. People usually see this process in reverse. Ordinarily, a voltage puts a particle in motion. Direct conversion reverses this process. It has been described is a linear accelerator, running backwards [90].

William Barr deserves a share of credit for demonstrating direct conversion. Over ten years he developed experimental and theoretical systems to prove the concept. Dr. Barr passed away in 2004 [72]. In 1982, he demonstrated an energy capture efficiency of 48% [76]. Wow! This efficient was realized on a real working fusion reactor, the TMX. That is why there is so much interest. Material from a fusion reactor has positive ions, negative electrons and neutrals. The exhaust is random. The basics of the machine used are shown here [74, 75, 76].

Image

The converter has to work this stuff into submission. First, it must get the particles to fly straight. It does this by using a magnetic expander [74]. This attempts to makes a beam out of the material. Next, the beam passes through a grounded shield. This insulates the fields inside the converter. Next, the electrons are suppressed. This is done by applying a negative voltage across the beam. Electrons are repulsed. Lastly, the ions push against a positive field. This raises the voltage of the collectors. These collectors become the positive side of a voltage drop in a wire. The converters efficiency theoretically depends on the number of collectors [91].

There are many fine points to running these machines. A full treatment cannot be done here. This principal has been used to recover energy in many ways [92]. There are several issues to be considered if using this in a power plant [78].

mvanwink5
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Re: My explaination of Direct Conversion

Post by mvanwink5 »

Why is a Maxwellian distribution assumed for a polywell pB11 reactor? There are specific reaction kinetic energies and the resulting alphas don't spend enough time to thermalize, right?

Couldn't the direct energy convertor be used to assist the vacuum pump effort by the affect of alpha concentration at the collection zones?

Other than that the explanation makes sense to me.
Counting the days to commercial fusion. It is not that long now.

D Tibbets
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Joined: Thu Jun 26, 2008 6:52 am

Re: My explaination of Direct Conversion

Post by D Tibbets »

Mattman's example is revealing. It is more than I had seen before of an actual application. I assume the TMX was a thermalized machine.

The Polywell is supposed to be non thermal, and for direct conversion non ignition. The alphas from P-B11 fusion do not remain in the Magrid space long enough to interact with the fuel ions. They are supposed to be close to their birth energy (plus or minus their proper motion at birth, perhaps ~ +/- 200 KeV. The Polywell is also a cusp machine which means the Alphas exit via small holes- beams mostly . This may allow for easier placement of "venitian blind" electrodes for direct conversion- increasing efficiency and / or simplifying placement. As the alphs are expected to be clustered around two seperate MeV energies, ease of higher efficiency conversion again would seem to be easier than a broad spectrum of thermalized fusion ions mixed with fuel ions.

I can also mention that I have seen a direct conversion scheme proposed for the diverter of a Tokamak. Not that they were trying to increase conversion efficiency over a thermal process, but to partially protect the diverter from the huge thermal loads expected in a Tokamak.

Dan Tibbets
To error is human... and I'm very human.

krenshala
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Location: Austin, TX, NorAm, Sol III

Re: My explaination of Direct Conversion

Post by krenshala »

D Tibbets wrote:Mattman's example is revealing. It is more than I had seen before of an actual application. I assume the TMX was a thermalized machine.

The Polywell is supposed to be non thermal, and for direct conversion non ignition. The alphas from P-B11 fusion do not remain in the Magrid space long enough to interact with the fuel ions. They are supposed to be close to their birth energy (plus or minus their proper motion at birth, perhaps ~ +/- 200 KeV. The Polywell is also a cusp machine which means the Alphas exit via small holes- beams mostly . This may allow for easier placement of "venitian blind" electrodes for direct conversion- increasing efficiency and / or simplifying placement. As the alphs are expected to be clustered around two seperate MeV energies, ease of higher efficiency conversion again would seem to be easier than a broad spectrum of thermalized fusion ions mixed with fuel ions.

I can also mention that I have seen a direct conversion scheme proposed for the diverter of a Tokamak. Not that they were trying to increase conversion efficiency over a thermal process, but to partially protect the diverter from the huge thermal loads expected in a Tokamak.

Dan Tibbets
I remember a post from Dr Nebel back before the Great Silence started that the alphas preferentially exited the magrid through the point cusps of each coil. A number of folks immediately jumped on that as showing direct conversion to be quite a bit easier to accomplish. I'm pretty sure that post/thread was in the News section...

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