Some questions

Discuss how polywell fusion works; share theoretical questions and answers.

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Zixinus
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Some questions

Post by Zixinus »

I want this tread to be for trivial questions regarding Polywell and fusion in general.

- What does therminalazation mean?

- I understand that ions accelerate into the centre of the cusps, due to electromagnetic potential given by the traped electrons. How are the electrons contained without the ions looking that way?

- Can anyone link the paper about side-reactions of p-b11 reaction?

- I once recall that lithium-6 + deuterium gives enormous energy and is easier to do then p-b11. How true is this?

drmike
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Post by drmike »

Thermalization means going from a non Maxwellian distribution of energy to a Maxwellian or Gaussian distribution. The electron guns and ion guns input particles at some high energy, and the process of thermalization converts it from uniform single energy to a distribution of energy. Look up "black body" for plots of particle energy distributions on the sun for an example.

For the polywell, the electrons are held by a magnetic field. They are more easily traped on field lines because they are lighter in mass and lower in energy than the ions.

The only side channel I can think of would be p + 11B -> 12C, which is stable.

Here's a nice cross section page.
You can figure out the answer from that data I think.

lambda0
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Post by lambda0 »

Some side reactions described here :
http://en.wikipedia.org/wiki/Aneutronic_fusion

11B + alpha -> 14N + n + 157 keV
11B + p -> 11C + n - 2.8 MeV
11B + p -> 12C + gamma + 16 MeV
As the hydrogen is not pure :
11B + D -> 12C + n + 13.7 MeV
D + D -> 3He + n + 3.27 MeV

lambda0
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Post by lambda0 »

I was thinking that side reactions may be really negligible for D-D fusion.

Primary reactions are :
D + D -> 3He + n + 3.27 MeV (50%) (1)
D +D -> T + p + 18.34 MeV (50%) (2)
Side reaction :
D + T -> 4He + n + 17.6 MeV (3)
D + 3He -> 4He + p (4)
In a system as a tokamak and some other fusion reactors, the tritium produced by (2) can react with D and produce 14 MeV neutrons (3) because the charged reaction products remain confined (in fact, it is important in a tokamak, as this allows the ignition mode, in which the plasma is heated by the alphas produced by the fusion when burning D-T).
However, in a Polywell, I think that the tritium is not confined (no recirculation), it directly escape from the reaction zone as the other products.
So, I suspect that in a Polywell burning D-D, the production of 14 MeV neutrons should be much lower than in a fusion reactors in which charged reaction products remain confined, as in tokamaks (burning also D-D).
The important reactions are (1) and (2), and the reaction (3) should be a negligible side reaction.

As in (1) and (2), most of the energy is carried by charged particles, a conversion by induction is interesting, and the neutron produced by (1) can be lost. It is also a quite "low" energy neutron (here, low=much lower than 14 MeV neutrons produced by D-T fusion) that can be shielded with conventional material already used in nuclear reactors.

The only major drawback I see, compared to p-B11 fusion, is the production of tritium (as it is not burned as in D-D tokamaks) that is highly radioactive and should be carefully collected, but this tritium can also be used for other applications : it decays to 3He, a nuclear fuel that can be burned through the reaction D+3He.
The advantage is that D-D fusion should be easier to obtain than p-B11.

For p-B11 :
(1') 11B + p -> 3*4He (main reaction)
(2') 11B + alpha -> 14N + n + 157 keV
(3') 11B + p -> 11C + n - 2.8 MeV
(4') 11B + p -> 12C + gamma + 16 MeV
As the hydrogen is not pure :
(5') 11B + D -> 12C + n + 13.7 MeV
(6') D + D -> 3He + n + 3.27 MeV
The side reactions (3'), (4') (and possibly (5'), (6')) always occur. Only the side reaction (2') will be negligible for the same reason that makes the D-T reaction negligible in a D-D Polywell (the alphas produced by the main reaction are not confined and escape directly).

Some confirmations that 14 MeV neutrons production should be much lower in a D-D Polywell than in a tokamak (or other equivalent concept) burning D-D ?
Is there somewhere some calculations that compare the radiations produced by a D-D and a p-B11 Polywell and take into account all the side reactions ?

MSimon
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Post by MSimon »

lambda0 wrote:Some side reactions described here :
http://en.wikipedia.org/wiki/Aneutronic_fusion

11B + alpha -> 14N + n + 157 keV
11B + p -> 11C + n - 2.8 MeV
11B + p -> 12C + gamma + 16 MeV
As the hydrogen is not pure :
11B + D -> 12C + n + 13.7 MeV
D + D -> 3He + n + 3.27 MeV
Hydrogen with zero (as in you cant find any to parts per billion) D and T is readily available. It is "waste gas" from the extraction of D and T.

MSimon
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Post by MSimon »

lambda0 wrote: The advantage is that D-D fusion should be easier to obtain than p-B11.
Actually no. Look at this graph.
Cross Sections

Where the reactivity starts to get useful (.1 barns - you get detectable reactions at .01 barns) the drive energies of D-D and pB11 are about equal. The required drive then for D-D is about 40 KV and for pB11 about 50 KV.

It is true you get measurable fusion at about 5 to 15 KV drive with D-D but power production is going to have a similar voltage regime as pB11.

Really. pB11 is not hard. Net power is hard. pB11 burning is not.

Zixinus
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Post by Zixinus »

Really. pB11 is not hard. Net power is hard. pB11 burning is not.
Great. Except we want to do net power.

MSimon
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Post by MSimon »

Zixinus wrote:
Really. pB11 is not hard. Net power is hard. pB11 burning is not.
Great. Except we want to do net power.
Doesn't every one.

One step at a time. We need the results of WB-7x before we go on to WB-100. We need to see if we can make use of POPS gain. Lots a stuff. Steady state control. Gas injection. B11 injection.

We need to take giant steps. One baby step at a time.

Zixinus
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Post by Zixinus »

One step at a time. We need the results of WB-7x before we go on to WB-100. We need to see if we can make use of POPS gain. Lots a stuff. Steady state control. Gas injection. B11 injection.

We need to take giant steps. One baby step at a time.
That's why I think we should try D-T or D-D first, and only after that stepping towards p-b11.

MSimon
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Post by MSimon »

Zixinus wrote:
One step at a time. We need the results of WB-7x before we go on to WB-100. We need to see if we can make use of POPS gain. Lots a stuff. Steady state control. Gas injection. B11 injection.

We need to take giant steps. One baby step at a time.
That's why I think we should try D-T or D-D first, and only after that stepping towards p-b11.
Other than dismissing D-T, have I suggested otherwise?

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