So, is the polywell a promising concept for achieving aneutronic fusion?

[Arubi Bushlee]

has anyone looked into the possibility of nuclear fusion without neutrons? it would make IEC fusion easier without all the neutrons running around making things radioactive and wearing them down.

I am wondering if p-B11 (proton-boron11) fusion is really an aneutronic fuel. deuterium-Helium3 fusion is aneutronic, until you account for the face D2D fusion can produce neutrons and in those reactions the neutrons carry a lot of energy. You could say, "well why not controll the speed at which the ions travel. They should be made fast enough to allow Deuterium-Helium3 fusion, but too slow for D2D (deuterium to deuterium) fusion." unfortunately for some reason, (one which I still am kinda fuzzy on, help me out with this) there is thermalization. When you shoot ions in all at the same speed, some end up faster than usual and some slower. The fast ions carry energy out of the reactor, and the slow ones are too slow to fuse. The fast ions can also facilitate some unwanted nuclear reactions in "aneutronic fuel" (i.e. D2D fusion.)

The point being p-B11 fusion produces neutrons every 1/1000 reactions. The total neutron energy is about 1/500 of the total energy produced. Is this still too much for the fuel to be considered aneutronic? (by definition it fits, but is it, you know good enough to not cause damage to a reactor or people around it?) If not are there any better aneutronic fuels.
*also in IEC fusion is there a way around the whole thermalization thing. I understand what happens I just have no idea how particles can start out at the same velocity (temperature) and than have some become slower and some become faster than the pack. To me it just sounds like the transfer of heat in reverse. Again I am not an expert, just looking to learn something.

P.S. the Polywell seems to be a good method of fusion. Any particular reason I haven't seen that around at all?

*edit* as thoroughly researched as other methods of fusion and IEC fusion.

 

[the_wolfman]

There are a number of alternative fusion fuels (D-He3, p-B, D-D catalyzed, etc) besides the standard D-T. There are both advantages and disadvantages to each of these fuels; however, they all requirer a higher operating temperature than D-T and they have lower reaction rates than D-T. Combined this means that they are much harder to ignite than D-T fuel. For this reason I consider these alternative fuels as 2nd generation fuels. The first generation fusion power plant will most likely use D-T simply because it is the easiest to ignite. Yes neutrons are a huge material issue for a D-T fusion plant, but they aren't what's preventing us from reaching breakeven in current experiments. Transport and stability limit current devices, and transport and stability usually gets worse as you go to higher temperatures.

Also most fusion research isn't dependent on the choice of "fuel." Yes there are going to be some difference between a D-T plasma and p-B plasma, but for the most part what we learn studying on type of plasma can be applied to other types of plasma. In fact most fusion research is done using D-D plasmas. Tritium operations is expense.

The polywell an other IEC devices are interesting, and I wish there was more money in the fusion budget so we could fund those and other alternative concepts. However, the truth is that current tokamaks have much better confinement than the polywell.

 

[Arubi Bushlee]

There are a number of alternative fusion fuels (D-He3, p-B, D-D catalyzed, etc) besides the standard D-T. There are both advantages and disadvantages to each of these fuels; however, they all requirer a higher operating temperature than D-T and they have lower reaction rates than D-T. Combined this means that they are much harder to ignite than D-T fuel. For this reason I consider these alternative fuels as 2nd generation fuels. The first generation fusion power plant will most likely use D-T simply because it is the easiest to ignite. Yes neutrons are a huge material issue for a D-T fusion plant, but they aren't what's preventing us from reaching breakeven in current experiments. Transport and stability limit current devices, and transport and stability usually gets worse as you go to higher temperatures.

Also most fusion research isn't dependent on the choice of "fuel." Yes there are going to be some difference between a D-T plasma and p-B plasma, but for the most part what we learn studying on type of plasma can be applied to other types of plasma. In fact most fusion research is done using D-D plasmas. Tritium operations is expense.

The polywell an other IEC devices are interesting, and I wish there was more money in the fusion budget so we could fund those and other alternative concepts. However, the truth is that current tokamaks have much better confinement than the polywell.

It's interesting you say that tokamaks have better confinement than polywells. The entire purpose of the polywell is the confinement. Electrons are easier to confine in magnetic fields than protons. The point of the polywell is to easily confine electrons, and then let their huge collection of negative charge attract the protons towards them. The point of the polywell is that you don't have to use so much energy to confine the electrons, and they then collectively confine the protons. Is this not the purpose of the polywell and why it has an advantage over the tokamak, because of the magnetic confinement?

 

[mfb]

Tokamaks confine both protons and electrons, and do so in a completely different way. You can scale them up to improve the confinement. With current experiments, tokamaks are much closer to break-even than any other device.

 

[the_wolfman]

The entire purpose of the polywell is the confinement.

The entire purpose of every confinement concept (tokamaks, stellarators, FRCs, RFP, etc) is confinement. The question is what concepts have the best confinement.

The point of the polywell is to easily confine electrons, and then let their huge collection of negative charge attract the protons towards them. The point of the polywell is that you don't have to use so much energy to confine the electrons, and they then collectively confine the protons.

This is the basic hypothesis upon which the polywell is designed. However, experimental tests have (unsurprisingly) shown that dynamics within the polywell are much more complex than this simple picture suggests. Understanding these complexities is key to improving the performance of the polywell.