Another Simple FAQ - DONE

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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KitemanSA
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Another Simple FAQ - DONE

Post by KitemanSA »

A reasonably simple question for the FAQ. Anyone?
How will nuclear ash removal be dealt with?
Last edited by KitemanSA on Wed Jun 02, 2010 12:49 am, edited 1 time in total.

WizWom
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Post by WizWom »

Without a method built in, the system will periodically have to be shut down. Then the vacuum pumps grab everything inside. Simple chemical level reactions can separate things.

For D-T, this is normal Helium. No problem - safe.
For D-D this is He3 & Helium4. He3/He4 would be separated, He3 kept.
For p-B this is normal Helium.

A method based on the mass spectrometer (cyclotron radius) to separate out the "ash" in a running plant using ion recirculation from cusp collectors could be done.

But it's all pointless. The low fusion cross section (for any reaction) means that fusion products will be trivial for run lengths even going to years, compared to volume of the input reactants (Hydrogen, Boron). You won't want to vent the vacuum pump low side without collection on the D-T machines, but the p+/B-11 machine will just release plain hydrogen and plain helium if you vent it (the Boron, with minimal cooling, will precipitate).
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hanelyp
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Post by hanelyp »

Charged fusion products have enough energy to easily escape the electrostatic confinement in a polywell, and escape the magnetic confinement after a number of passes through the core, projected to be on the order of 1000 passes. These ions make their way to the outer wall of the chamber, neutralize, and may then be removed as neutral gas. Any ions outside the magrid will tend to be excluded from entering by the magrid potential.

Related:
If the outer wall has an electric potential a little short of the ion energy relative to the core, the ion energy up to that potential may be collected by direct conversion.

KitemanSA
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Post by KitemanSA »

Draft answer. Comments?
The fusion “ash” is one or more charged particles, sometimes with a neutron. Being neutral, the neutrons are unaffected by the potential well or the MaGrid and will remove themselves from the core, unfortunately radio-activating the chamber wall, etc. in the process.

The charged fusion products will have enough energy to easily escape the electrostatic confinement in a polywell, and escape the magnetic confinement after a number of passes through the core, projected to be on the order of 1000 passes. These ions make their way to the outer wall of the chamber (or the direct conversion device if it exists), neutralize, and may then be removed as neutral gas. Any ions outside the MaGrid will tend to be excluded from entering by the MaGrid potential.

Once the “ash” has been removed from the chamber, simple chemical level reactions can separate things where needed. Also, mass spectrometry methods could be used for isotope seperation.

For D-T, this is normal Helium + neutron.
For D-D this is Tritium+p or He3+n.
For p-B this is normally just Helium.

D Tibbets
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Post by D Tibbets »

KitemanSA wrote:Draft answer. Comments?
The fusion “ash” is one or more charged particles, sometimes with a neutron. Being neutral, the neutrons are unaffected by the potential well or the MaGrid and will remove themselves from the core, unfortunately radio-activating the chamber wall, etc. in the process.

The charged fusion products will have enough energy to easily escape the electrostatic confinement in a polywell, and escape the magnetic confinement after a number of passes through the core, projected to be on the order of 1000 passes. These ions make their way to the outer wall of the chamber (or the direct conversion device if it exists), neutralize, and may then be removed as neutral gas. Any ions outside the MaGrid will tend to be excluded from entering by the MaGrid potential.

Once the “ash” has been removed from the chamber, simple chemical level reactions can separate things where needed. Also, mass spectrometry methods could be used for isotope seperation.

For D-T, this is normal Helium + neutron.
For D-D this is Tritium+p or He3+n.
For p-B this is normally just Helium.
...
The tritium and helium3 ash from D-D fusion could then be fed back into the reactor as additional fuel. The neutron ash could also generate new fuel if a blanket of Boron 10 is used to absorb them, with subsequent breakdown of the excited boron 11 into lithium and tritium.
If the systems works, this passive extraction of the fusion ash provides a significant advantage over Tokamaks which do not passively allow the ash to escape.

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

D Tibbets
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Post by D Tibbets »

WizWom wrote:Without a method built in, the system will periodically have to be shut down. Then the vacuum pumps grab everything inside. Simple chemical level reactions can separate things.

For D-T, this is normal Helium. No problem - safe.
For D-D this is He3 & Helium4. He3/He4 would be separated, He3 kept.
For p-B this is normal Helium.

A method based on the mass spectrometer (cyclotron radius) to separate out the "ash" in a running plant using ion recirculation from cusp collectors could be done.

But it's all pointless. The low fusion cross section (for any reaction) means that fusion products will be trivial for run lengths even going to years, compared to volume of the input reactants (Hydrogen, Boron). You won't want to vent the vacuum pump low side without collection on the D-T machines, but the p+/B-11 machine will just release plain hydrogen and plain helium if you vent it (the Boron, with minimal cooling, will precipitate).
I don't think ash build up is trivial. If a reactor is producing 1 GW of power it will be producing ~ 10^21 fusions per second.* In a Tokamak you might have 10^19-20 fuel ions per cubic meter and perhaps a few hundred cubic meters in the torus. So, it would take only a few seconds for the fusion ash ions to build up to a significant percentage of the total population if they are not aggressively extracted/ diverted from the plasma. Keep in mind that the total amount of fuel ions in a working Tokamak (or smaller Polywell) will only be ~ 10 to 100 milligram of hydrogen.

* 10^12 D-D fusions per second will produce ~1 watt of fusion power.

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

KitemanSA
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Post by KitemanSA »

Second draft answer. Comments?
The fusion “ash” is one or more charged particles, sometimes with a neutron. Being neutral, the neutrons are unaffected by the potential well or the MaGrid and will remove themselves from the core, unfortunately radio-activating the chamber wall, etc. in the process.

The charged fusion products will have enough energy to easily escape the electrostatic confinement in a polywell, and escape the magnetic confinement after a number of passes through the core, projected to be on the order of 1000 passes. These ions make their way to the outer wall of the chamber (or the direct conversion device if it exists), neutralize, and may then be removed as neutral gas. Any ions outside the MaGrid will tend to be excluded from entering by the MaGrid potential.

Once the “ash” has been removed from the chamber, simple chemical level reactions can separate things where needed. Also, mass spectrometry methods could be used for isotope seperation.

For D-T, this is normal Helium + neutron.
For D-D this is Tritium+p or He3+n.
For p-B this is normally just Helium.

The tritium and helium3 from D-D fusion could then be fed back into the reactor as additional fuel. The neutrons could also generate new fuel if a blanket of Boron 10 is used to absorb them, with subsequent breakdown of the excited boron 11 into lithium and tritium.
If the systems works, this passive extraction of the fusion ash provides a significant advantage over Tokamaks which do not passively allow the ash to escape.

WizWom
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Post by WizWom »

The fusion products won't do the 1000 passes through the core, that's the electrons.
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KitemanSA
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Post by KitemanSA »

WizWom wrote:The fusion products won't do the 1000 passes through the core, that's the electrons.
Dr. Nebel wrote:4. As for Mr. Tibbet’s questions relating to alpha ash, these devices are non-ignited (i.e. very little alpha heating) since the alpha particles leave very quickly through the cusps. If you want to determine if the alphas hit the coils, the relevant parameter is roughly the comparison of the alpha Larmor radius to the width of the confining magnetic field layer. I’ll leave that as an “exercise to the reader” as well.
Subsequently, it was determined that with a power size reactor the number of passes thru the core to find a cusp was about 1000 (IIRC total area / cusp area). That is the basic number until better ones come along. Also, the higher the B the more passes due to the smaller cusp areas, in theory.

D Tibbets
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Post by D Tibbets »

KitemanSA wrote:
WizWom wrote:The fusion products won't do the 1000 passes through the core, that's the electrons.
Dr. Nebel wrote:4. As for Mr. Tibbet’s questions relating to alpha ash, these devices are non-ignited (i.e. very little alpha heating) since the alpha particles leave very quickly through the cusps. If you want to determine if the alphas hit the coils, the relevant parameter is roughly the comparison of the alpha Larmor radius to the width of the confining magnetic field layer. I’ll leave that as an “exercise to the reader” as well.
Subsequently, it was determined that with a power size reactor the number of passes thru the core to find a cusp was about 1000 (IIRC total area / cusp area). That is the basic number until better ones come along. Also, the higher the B the more passes due to the smaller cusp areas, in theory.
The 1000 passes (as per Dr Nebel) are for ions that are traveling too fast to be contained by the potential well- such as alpha particles with energies of several MeV. Their containment time/ number of passes is governed by the Wiffleball magnetic containment. I have seen mirror confinement numbers of ~ 60 passes, and simple cusp confinement lasting only a few passes. Fuel ions with energies just below that of the potential well may be contained for much more than a 100,000 passes. The confinement time for electrons is ~ 100,000 passes (including recirculation).

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

KitemanSA
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Post by KitemanSA »

Final answer.
The fusion “ash” is one or more charged particles, sometimes with a neutron. Being neutral, the neutrons are unaffected by the potential well or the MaGrid and will remove themselves from the core, unfortunately radio-activating the chamber wall, etc. in the process.

The charged fusion products will have enough energy to easily escape the electrostatic confinement in a polywell, and will escape the magnetic confinement after a number of passes through the core. These ions make their way to the outer wall of the chamber (or the direct conversion device if it exists), neutralize, and may then be removed as neutral gas. The gas must be removed by a very high capacity, very low pressure pump, but the power needed should not be excessive. According to Dr. Nebel,[1] "If I am reading this correctly, the pumping power is about 60,000 liters/second. This is ~ 30 times more than the WB-7. It doesn't take a lot of power. Our system takes ~ 500 watts of power. ITER probably requires 10-20 kW."

Once the “ash” has been removed from the chamber, simple chemical level reactions can separate things where needed. Also, mass spectrometry methods could be used for isotope seperation.

For D-T, this is normal Helium + neutron.
For D-D this is Tritium+p or He3+n.
For p-B this is normally just Helium.

The tritium and helium3 from D-D fusion could then be fed back into the reactor as additional fuel. The neutrons could also generate new fuel if a blanket of Boron 10 is used to absorb them, with subsequent breakdown of the excited boron 11 into lithium and tritium.
If the systems works, this passive extraction of the fusion ash provides a significant advantage over Tokamaks which do not passively allow the ash to escape.


[1] viewtopic.php?t=1211&highlight=system+t ... atts+power
The above answer is now inserted in the FAQ. At this point, this topic is done. If you want to make further comments, either PM me directly or start a new topic please.

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