Talk-Polywell.org

I would like to pose a question to the page....

Could a Fusor type system reach p-B11 potential? I am thinking we could coat the grid with B11. Then when the injected protons hit the grid they can/will fuse with the boron.

Am I missing something?

This system seems like it would solve many of the Fusor issues. The proton collisions with the grid would trigger fusion rather than hinder it. The Boron would shield the grid from being destroyed and could be re-applied to the grid once it has been used. What sort of voltage would be necessary to reach p-B11 potential in a fusor?


Any comments?

It would melt from the electrons hitting the grid long before the well reached the necessary conditions for significant p-b11 fusion. Even 1% is way too high, and iirc they usually operate around 5% loss.

To begin with, hydrogen-boron fusion requires ion energies or temperatures almost ten times higher than those for D–T fusion. For any given densities of the reacting nuclei, the reaction rate for hydrogen boron achieves its peak rate at around 600 keV (6.6 billion degrees Celsius or 6.6 gigakelvins) while D–T has a peak at around 66 keV (730 million degrees Celsius).[3]

http://en.wikipedia.org/wiki/Aneutronic_fusion

You can indeed get fusion by directing a beam of hydrogen ions at a block of boron. The problem is that only a small fraction of the ions will actually fuse. Most of them will simply slow down to a stop through collisions with electrons (mostly). You might get 100 times more energy out of a fusion reaction as you have to invest to accelerate the ion, but if you have to accelerate 1000 ions to get one fusion, you lose.

Art Carlson wrote:You can indeed get fusion by directing a beam of hydrogen ions at a block of boron. The problem is that only a small fraction of the ions will actually fuse. Most of them will simply slow down to a stop through collisions with electrons (mostly). You might get 100 times more energy out of a fusion reaction as you have to invest to accelerate the ion, but if you have to accelerate 1000 ions to get one fusion, you lose.

Art,

Two things:

1. Contact me. My e-mail is at the top of the sidebar:

http://powerandcontrol.blogspot.com/

2. Even if such a device operated at a loss it might be useful for experimental purposes. In any case it would be the first continuously operating pB11 fusion reactor.

Simon - check out DWA - dielectric wall accelerator. There is a company here in Madison that is using LLNL's invention for proton radiation therapy (but unfortunately for me they are doing the work at UC Davis). They generate high energy (200 MeV) protons in about a meter. I would think higher currents and lower energy would be possible in a lot smaller package.

TallDave wrote:It would melt from the electrons hitting the grid long before the well reached the necessary conditions for significant p-b11 fusion. Even 1% is way too high, and iirc they usually operate around 5% loss.

What electron would hit the grid?

If you meant protons then we don't have to inject any protons until the target is up to the right voltage.

Why can't we cool it?

I am thinking a non-conductive coolant inside a conductor which carries the charge then an inch or so (just a guess) of B11 surrounding it. (similar in design to the mag-grip for the polywell) The coolant doen't necessarily need to be anything exotic but I suppose a superconductor carrying the charge would be more efficient.

Finally the "grid" can and should be soild since we want the protons to hit it.

clonan wrote:
What electron would hit the grid?

The electrons that make up the potential well.

Let me see if I understand this. Do you really need a grid? can't you use a metal wall coated with B11? Of course the wall is biased negatively, (Charged negatively to a large value). Then stand back and shoot it with an ion gun. Then when you get a fusion you get some secondary electrons but they are relatively low energy, and they will want to go to your ion gun anyway, if they're free. So how do the electrons heat the wall?

Roger wrote:

clonan wrote:
What electron would hit the grid?

The electrons that make up the potential well.

This is a Fusor design...there is no potential well...no wiffleball effect...

All electrons are confined to the conductor which is coated in B11

drmike wrote:Simon - check out DWA - dielectric wall accelerator. There is a company here in Madison that is using LLNL's invention for proton radiation therapy (but unfortunately for me they are doing the work at UC Davis). They generate high energy (200 MeV) protons in about a meter. I would think higher currents and lower energy would be possible in a lot smaller package.

I think it is a pulsed system. Do you have any details on operation? All I could find were abstracts.

Found something. It is buried in the piece:

http://arxiv.org/ftp/physics/papers/0010/0010011.pdf

This is a Fusor design...there is no potential well...no wiffleball effect...

Fusors always have a potential well, or at least a gradient somewhere; it's how they accelerate the ions. It could have a virtual or real electrode, but they're all going to melt pretty fast at p-B11 energies, either from ions hitting them or electrons, depending on the design.

Polywell is basically a fusor with a virtual electrode and a magnetically shielded positive grid, and the added bonus of the WB effect to give you better electron density.

I'm sure with the right setup, you can get a well/gradient over 600keV and get a few p-B11 fusions one way or another before it melts. I'm not sure how much that would tell you that's useful in regards to developing p-B11 as a power source, but it might be fun!

D-3He has been done in fusors (University of Wisconsin) and you can get grids that will handle high energy. Consequently, P-11B is also probably doable. The best material we have used for grids is a Tungsten-Rhenium alloy. Tungsten works at high temperatures and the Rhenium allows you to weld it with a spot welder.
However, as many of you pointed out these systems won't show net gain. Coulomb scattering always beats fusion in these systems. Fusion power scales linearly with current as does the power in. Consequently, Q is independent of the current.

TallDave wrote:It would melt from the electrons hitting the grid long before the well reached the necessary conditions for significant p-b11 fusion. Even 1% is way too high, and iirc they usually operate around 5% loss.

To begin with, hydrogen-boron fusion requires ion energies or temperatures almost ten times higher than those for D–T fusion. For any given densities of the reacting nuclei, the reaction rate for hydrogen boron achieves its peak rate at around 600 keV (6.6 billion degrees Celsius or 6.6 gigakelvins) while D–T has a peak at around 66 keV (730 million degrees Celsius).[3]

http://en.wikipedia.org/wiki/Aneutronic_fusion

Um, Boron is one of the highest temperature solids, melting point 3700 degrees or so. Not likely to melt. In a silver alloy (thermal and electrical conduction excellence) core, boron coated grid may be advantageous. Just cause a fusion reaction itself is at 6.6 billion degress celsius doesnt mean that the grid would be anywhere near being heated to that level. The steering fins on ICBM MIRVs are zirconium diboride.

The question of the first wall material is a hot topic in tokamak research. The first machines were stainless steel because it was the easiest way to make a good vacuum.
As the power levels increased, first the limiters and divertor plates and later the whole first wall were covered with graphite tiles. Graphite has enormous advantages: one of the highest thermal conductivities known, only a moderate electrical conductivity (important during disruptions), good machinability, sublimation instead of melting, a tendency to outgas, and a low Z (so impurities that do get into the plasma don't radiate so much). In addition, there are some complex but highly beneficial feedback effects in interaction with the plasma. Unfortunately, the erosion rate is huge, it tends to form dust, and - worst of all - it co-deposits with tritium, leading to unacceptably large tritium inventories.
It took several years, but the community is now convinced that the first wall, or at least the divertors will have to be made of tungsten, despite the lower thermal conductivity, higher electrical conductivity, poor machinability, tendency to lose its geometry by melting, high Z, and some severe radiological problems. Surprisingly, it seems to be possible to keep the level of tungsten ions in the central plasma at the low level required. (Molybdenum has similar properties, some better, some worse, but apparently loses out against tungsten over all.)
In addition to the choice of bulk material, it has been found beneficial to coat the walls with a thin (monolayer) layer of boron (!) or silicon compounds. Mostly this works as a getter to lower the oxygen levels.
The polywell will face similar trade-offs but may come to a different conclusion. In particular, if the thermal load is (as is the dream) primarily bremsstrahlung radiation and alpha particles, the erosion process will be very different from that due to the high-power, low-temperature plasma in a tokamak divertor.

The polywell will face similar trade-offs but may come to a different conclusion. In particular, if the thermal load is (as is the dream) primarily bremsstrahlung radiation and alpha particles, the erosion process will be very different from that due to the high-power, low-temperature plasma in a tokamak divertor.

This sounds like expensive and time consuming technical development? Isnt it better to aim for an esier fuel (D-Doch D-T) and steam cycle energy extraction in the first place? If the polywell contraption should show any signs of life.