Fusion Will Never Work

[Axil]

The problem with fusion is economic. It is an anemic energy producer, especially aneutronic boron fusion. Next, boron fusion will produce enough neutrons to activate its structural material and make O&M difficult so why go through all the effort. High energy electrons and ions are far more erosive to the reactor structure than neutrons are so why all the push and excitement for aneutronic boron fusion. It is a fool’s errand. For these reasons I like a thermal neutron rich fusion/fission hybrid approach.

Reference:

http://www-ferp.ucsd.edu/LIB/MEETINGS/0 ... sakura.pdf


ITER D-T fusion power production overview.


ITER power output
Fusion power = 500 MW
Thermal power = 150 MW
Electric power = 50 MW

DEMO power output
Fusion power = 3000 MW
Thermal power = 700 MW
Electric power = 233 MW

For such a big reactor design to produce such little power output is not good economics

[D Tibbets]

A few comments about the posts since my last post. My understanding that the magnetic confinement of the electrons (through Wiffleball formation) is ~ 10,000 passes/ orbits before a electron hits one of the narrow cusps and exits. Recirculation then retrieves ~ 9/10 of the escaping electrons giving an effective containment of 100,000 passes. This benifits the energy balance. Perhaps almost as important is that I understand these recirculated electrons are monoenergetic and directeded towards the center, just like the new electrons injected from the electron guns. This means that the thermalization of the electrons is limited by their lifetime of ~10,000 passes. With electron speeds in WB6 of ~10^9 cm/s , assume a ~ 5X10^8 cm/s average speed . That devided by ~ 25 cm Wiffleball diameter (a conservaeive guess as this would be very close to the magnet cases, if not within them) = 20 million passes per second. This devided by 10,000 passes gives a 0.5 ms lifetime for the nonrecirculated electrons. So, recirculation saves input energy, but it also decreases the effective thermalization time of the electron population by a factor of ten!

The alphas traveling at ~ 2 Mev in a P-B11 machine will be decellerated a little by the ~ 200 KeV potential well. The resulting ~1.8 MeV particle will hit the magnetic field and be turned with a gyroradius dependant on the magnetic field strength. In another thread months ago R. Nebel pointed this out. Once the machine has an adiquate radius and B field the alphas will be magnetically contained. I don't recall the numbers, but I believe 1 meter and a couple of Teslas will do it, The alphas escape through the narrow cusps after ~ 1000 tries (according to R. Nebel). They will not hit the magrids. There is no strange physics in this, only straight forward magnetic principles.

I don't understand the derivation of Tokamac electrical output. Is seems the thermal and electrical conversions are redundant. If ITER produces 500 MW of fusion power, almost all of this energy will be captured as heat. The conversion to electricity might be 30% efficient, so gross electrical output would be 150 MW (three times as high as predicted in the post).

The comment about the insignificance of aneutronic fusion advantages is incomplete. The neutron radiation loads on the magrids (which need to be kept at cryogenic temperatures inside) are much ,much less (heating of the magrids). Also, much less neutron damage to the superconductors. The alphas allow for the ~ 2-3X increased efficiency of direct conversion to electric power than thermal cycles. All other things being equal, this allows the reactor to be 2-3 times smaller, or to have a 2-3 times smaller Q for the same final electrical output.
The fusion output of a D-D reactor would be ~ 50% neutrons and 50% charged particles. Both will cause spallation concerns. In fact, I speculate that the advantages of decreasing spallation may be great enough to justifly a direct conversion scheeme for the charged particles (tritium and helium 3 nuclei). This would decrease spallation and also possibly increase final electrical conversion efficency to as much as 50-60% (30% from neutron thermalization, and 80% from direct conversion from tritium and helium 3 ions. It would presumably be more difficult, as there would be a greater energy spread in the charged particles, compared to P-B11 fusion alphas.
While there is secondary transmutations of structures in an aneutronic machine, it will be far less than a neutron producing machine- either fusion or fission based..

Fusion/ fission hybirds are a fallback position if D-D fusion (with resultant neutron production) can only approach break even or only slightly surpass it.
In my layman's opinion, a Tokamak is not sutable for a fusion/ fision hybird because it will have a hard time producing enough tritium (derived from neutron reactions) to feed itself, yet alone provide excess neutrons to drive fission reactions.

Dan Tibbets

[alexjrgreen]

Shouldn't fusion products have enough energy that, even if they hit the B-field perfectly perpendicularly, that they have an effectively infinite gyroradius and punch right through? And, if they hit a cusp, won't the particle simply go through the cusp and break free as the field lines bend back behind the magrid?

Don't worry none. 'Polywell' appears to be a device that can defeat the laws of physics so long as enthusiasts talk long enough about what they want the electrons and ions to do. Eventually, the electrons and ions will hear the messages and obey (once an actual experiment to measure them happens, of course).

I'm describing what I can see in the WB7 photo...

[alexjrgreen]

The electrons that leave through the centre cusps get recirculated by the magrid. The ions that tag along for the ride mostly get recirculated too.

First, there is no indication that the fuel ions leave in any significant number, nor that they recycle at all. Those fuel ions that have NOT been upscattered stay in the well. Those that have are lost to the chamber wall. Simple. Why complicate it by assuming tag-along behavior and recirculation by ions that seems contrary to physics?

There's a limit to how far you can treat the electrons and ions separately.

Some of the ions tag along, and some of them are recirculated.

[D Tibbets]

Shouldn't fusion products have enough energy that, even if they hit the B-field perfectly perpendicularly, that they have an effectively infinite gyroradius and punch right through? And, if they hit a cusp, won't the particle simply go through the cusp and break free as the field lines bend back behind the magrid?

Don't worry none. 'Polywell' appears to be a device that can defeat the laws of physics so long as enthusiasts talk long enough about what they want the electrons and ions to do. Eventually, the electrons and ions will hear the messages and obey (once an actual experiment to measure them happens, of course).

Rereading chrismb's response, it occurs to me that this sounds like a good discription of what occurs with quantum mechanics


Dan Tibbets

[Axil]

I don't understand the derivation of Tokomak electrical output. Is seems the thermal and electrical conversions are redundant. If ITER produces 500 MW of fusion power, almost all of this energy will be captured as heat. The conversion to electricity might be 30% efficient, so gross electrical output would be 150 MW (three times as high as predicted in the post).

The liquid blanket converts fusion power to thermal power. The efficiency of this conversion is only as good as the design of the blanket. The blanket absorbs the gamma rays, ions, high energy electrons, and neutrons produced by fusion. These various manifestations of fusion energy produce heat in the blanket by increasing the vibration of atoms in the blanket. They also transmute the elements in the blanket to other elements.

A blanket that is 100 % efficient will fully surround the fusion energy source, and absorb all the various types of radiation produced by fusion. For example, the totally effective blanket will fully protect the structure of the fusion reactor from fusion energy. Fusion energy that goes into damaging the first wall and diverters or transmuting the structure of the reactor is wasted energy.

The design of the Tokomak is not well suited to the implementation of a 100% effective blanket. Herein lies the difference and the inefficiency in the fusion power and thermal power conversion process. This is also why the fusion energy from the Tokomak is so hard on the structure of the Tokomak structure.

The alphas traveling at ~ 2 Mev in a P-B11 machine will be decellerated a little by the ~ 200 KeV potential well. The resulting ~1.8 MeV particle will hit the magnetic field and be turned with a gyroradius dependant on the magnetic field strength. In another thread months ago R. Nebel pointed this out. Once the machine has an adiquate radius and B field the alphas will be magnetically contained. I don't recall the numbers, but I believe 1 meter and a couple of Teslas will do it, The alphas escape through the narrow cusps after ~ 1000 tries (according to R. Nebel). They will not hit the magrids. There is no strange physics in this, only straight forward magnetic principles.

Re: “alphas will be magnetically contained”

IMHO, this is not good.

The ions that are magnetically contained will orbit and loss energy to the boron plasma until that reach the optimum cross sectional energy for the ion to neutron reaction. (a,n).

At that energy level, boron will be transmuted into N13 and C13. C13 will transmute to O16. Then O16 will poison or totally kill the boron fusion process.

See:

http://authors.library.caltech.edu/9964/1/BONpr56b.pdf


It is best to clear all fusion ash to a perfect vacuum, reintroduce fresh boron plasma, and then reinitial plasma compression.


The difficulty in doing this is one reason why I think that boron fusion won’t work in polywell.

A reactor design like Helion can clear the ash to a diverter after each pulse, so the prospects of boron fusion under the Helion architecture is much improved.

The fusion output of a D-D reactor would be ~ 50% neutrons and 50% charged particles. Both will cause spallation concerns. In fact, I speculate that the advantages of decreasing spallation may be great enough to justifly a direct conversion scheeme for the charged particles (tritium and helium 3 nuclei). This would decrease spallation and also possibly increase final electrical conversion efficency to as much as 50-60% (30% from neutron thermalization, and 80% from direct conversion from tritium and helium 3 ions. It would presumably be more difficult, as there would be a greater energy spread in the charged particles, compared to P-B11 fusion alphas.

The reaction cross section for charged particles with the fusion medium might be so great that charged particles will not make it far enough to react with the charged particles conversation system.


IMHO, a 100% efficient thermalizing fission molten salt blanket is the safest and best bet to achieve thermal/electric conversion efficiency of 50% or more, limited only by heat and neutron tolerance of the blanket containment material.

Fusion/ fission hybrids are a fallback position if D-D fusion (with resultant neutron production) can only approach break even or only slightly surpass it.

In my layman's opinion, a Tokamak is not suitable for a fusion/ fission hybrid because it will have a hard time producing enough tritium (derived from neutron reactions) to feed itself, yet alone provide excess neutrons to drive fission reactions.

In a fusion/ fission hybrid, there is an abundant oversupply of neutrons. The fission blanket also produces a goodly amount of tritium as a waste product. If this waste tritium from fission is not enough then a fusion neutron source of only 10e17 neutrons per second or less is enough to keep the fusion/fission reaction going. With this generous neutron budget, adding some small amount of lithium 6 to the blanket will produce abundant tritium for D-T fusion. Lithium 7 will also produce tritium in a high energy fusion neutron energy spectrum.

[D Tibbets]

Concerning Axil's last post.
Any radiation that does not completely escape the reactor, water blanket, etc. will eventually be heat (only exception I can think of would be transmutted materials that have a half life near the lifetime of the reactor- or are removed quickly (like the generated tritium)). The heat that builds up, has to go somewhere, if not into the water blanket to produce steam, the excess heat will be lost to the room. This is similar to the heat that goes up the smoke stack in a coal plant. I thought this was included in the ~30% efficiency of these plants, but perhaps not...

My comments about the lifetimes of fusion ions within the magrid is hearsay that I have picked up from R. Nebel's comments. The fusion ions are contained, but very poorly, compared to the fuel ions. They do not have adiquate time / collision oppertunities to react with the fuel ions to any appreciable extent.
I once speculated in a post thet the tritium and He3 produced from D-D fusion in a Polywelll could then interact with additional deuterium in the machine to magnify the fusion output. Dr. Nebel shot this down, stating essentially the above. The high energy ions are two fast to be contained by the potential well, and the magnetic containment is too short to allow these secondary fusions in any significant numbers. The He3 and tritium would have to be collected from the vacuum pump output, purified, and fed back into the reactor at appropiate energies. This is completly different from a Tokamac type of plasma where the ash buildup is an issue.
Keep in mind that R. Nebel said that the alphas would bounce around inside the magrid about a thousand times before finding a cusp and escaping. The electrons bounce around ~ 100,000 times (with recirculation). Without recirculation the electrons bounce around ~ 10,000 times before finding a cusp. This 10 fold improvement in electron confinement compared to high energy alpha confinement is presumably an example of the greater efficieny of electron confinement by magnetic bottles. The fuel ions bounce around perhaps millions (many millions?)of times before they manage to both upscatter enough to escape the potential well and then find a cusp.

In the fusion/ fission hybird I had not concidered the excess neutrons from fission that could be used to produce perhaps more than enough tritium. It makes Tokamaks as the fusion half more pratical, though still extreamly expensive. But, if they can get the FRC reactor or the Polywell to work well enough with D-T, or even better D-D, then ...

Dan Tibbets

[KitemanSA]

There's a limit to how far you can treat the electrons and ions separately.

Some of the ions tag along, and some of them are recirculated.

Given the excess of electrons in the well, why would the few that escape the cusps cause any ions to "tag along"? Especially given that they turn right around and come back in anyway.

[Axil]

Fusion people would not use water as a blanket material. They would use either Lithium/lead or molten fluoride salts of lithium and beryllium and/or maybe sodium because of their nuclear properties and heat exchange advantages (High thermodynamic conversion efficiency)

Unless fusion products find their way into the blanket, the heat they produce will not get into the heat exchanger and then into the electric turbo generators. From the ITER and DEMO design numbers I quoted in the previous post, it seems that a high percentage of the fusion radiation is vented in various ways to the outside world as waste heat.

Also, when someone gets Boron fusion to work to some level, then that’s when the real design work to get the “Q” up to 30 to 50 will begin. I won’t say it is impossible for high Q boron fusion to work even if deep in my heart I think it is so. In any event, this boron fusion work will take a very very long time and take much much effort.

But, if they can get the FRC reactor or the Polywell to work well enough with D-T, or even better D-D, then…

This is my hope.

[chrismb]

In ITERs case, of course it will produce no electrcity whatsoever. There is no attempt at all to actually recover energy in this experiment. This is why I harp on about ITER being a badly conceived project which doesn't actually serve much purpose. It seems to me to be more a political experiment in the acceptability of fusion energy research that a scientific one in the viability of fusion energy!

[alexjrgreen]

In ITERs case, of course it will produce no electrcity whatsoever. There is no attempt at all to actually recover energy in this experiment. This is why I harp on about ITER being a badly conceived project which doesn't actually serve much purpose. It seems to me to be more a political experiment in the acceptability of fusion energy research that a scientific one in the viability of fusion energy!

Given the experience of demonstrations against nuclear power stations, perhaps that's not surprising.

[MSimon]

Also, when someone gets Boron fusion to work to some level, then that’s when the real design work to get the “Q” up to 30 to 50 will begin. I won’t say it is impossible for high Q boron fusion to work even if deep in my heart I think it is so. In any event, this boron fusion work will take a very very long time and take much much effort.

The ultimate Q for pB11 at the resonance peak is about 22. At the cross section peak around 8.

If you are not trying to make tritium I'd skip the liquid metals bit and use water for the moderator/coolant in a D-D device. It is cheap. Well understood. A very good moderator. Good thermal properties. Equipment for handling it is widely available.

[Art Carlson]

The ultimate Q for pB11 at the resonance peak is about 22. At the cross section peak around 8.

Where does this number come from? (Not trying to make trouble, just meekly seeking information.) I suppose the fusion reactivity is for a p-beam streaming against a B11-beam (but it could possibly be for monoenergetic but isotropic distributions, or even <shudder> Maxwellian distributions). I can't imagine what you would take for the loss term (the denominator of Q) if not bremsstrahlung, but what assumption will land you at Q = 22 (or 8)?

[MSimon]

The ultimate Q for pB11 at the resonance peak is about 22. At the cross section peak around 8.

Where does this number come from? (Not trying to make trouble, just meekly seeking information.) I suppose the fusion reactivity is for a p-beam streaming against a B11-beam (but it could possibly be for monoenergetic but isotropic distributions, or even <shudder> Maxwellian distributions). I can't imagine what you would take for the loss term (the denominator of Q) if not bremsstrahlung, but what assumption will land you at Q = 22 (or 8)?

It is for a no loss device only considering the acceleration energy. Beam-Beam interactions. In other words the Carnot calculation for an ideal Polywell. Reality is likely to be somewhat different.

[KitemanSA]

I'm describing what I can see in the WB7 photo...

PLEASE remember that the WB7 photo on the EMC2FDC site is a DIAGNOSTIC run. There is no fuel, only electrons and neutral He gas which gets locally excited and then radiates where it gets hit by electrons.
The glow pattern you are seeing simply tells you where the electrons go, not where the fuel goes. There is no fuel there. Glow outside the MaGrid is due to electrons impacting neutral He outside the MaGrid, not fuel ions exiting a cusp and radiating outside the MaGrid. Nothing can be learned about the behavior of the fuel from that picture.