Some Rough Ideas which need refining into a formal blog post

[mattman]

Hello guys,

Looking for feedback on the following post:


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The following are the first generation DD reactions:

D + D --> (Tritium at 1.01 MeV) + (Proton at 3.02 MeV)
D + D --> (Helium3 at 0.82 MeV) + (Neutron at 2.45 MeV)

Each reaction is equally likely to happen. What happens to the products?


1. The free standing proton is stable, it is not going to pick
up an electron and make hydrogen, because electrons on hydrogens fly
off at ~1/77,000 that temperature; the proton is moving too fast to
grab an electron. Could the proton could undergo Inverse Beta Decay?
This process needs allot of neutrons flying around and I do not know if the neutrons produced are sufficient. Somehow the neutrons are incite the production of antineutrinos (?) needed for this reaction.

(Proton at 1.022 MeV) + (antineutrino) --> neutron + electron

The proton would have 3 times the energy needed to undergo this step.



2. Tritium. There are LOTS of other reactions that can occur
with this tritium, but they won't because their cross section is too
low. Cross section is measure of the fusibility of something; the
higher it is the more likely it is to happen. You can get it from a
graph like this one:

http://farm4.static.flickr.com/3350/342 ... f330b5.jpg.

Where was Bussard on this graph? In WB-6 he had a well of about
10,000 volts. He dropped deuterium down that well so when it hit the
center it had 10 KeV of energy (charge of one times 10,000 volts).
Where he is, he can barely do DD fusion. You will notice that he is
not even on the graph. Now, lets say he made a well of 25,000 volts.
He would need a drive voltage of about 30 kV. This is definitely
do-able (a typical power line is about 110 kV, there are some lines as
high as 230 kV). His cross sections jump. For DT they go up about
100 fold for DD about 150 fold and for TT about 200 fold.

Lets crank this up. Say Bussard ran his Polywell at a drive
voltage for typical power lines (110 kV). He would have a well at
about 92 KV. He would be at the sweet spot for DT fusion; its peak
cross section. DT fusion would be about 5,000 times more likely than
in the original WB6 experiment. DT is a pain, because it is
radioactive, you would need a whole system to deal with this, such
systems do exist. Also, the TT reactions, the helium3 reactions and
the DHe reactions all become do-able, but they are going to happen in
a very small amount. I sat down and estimated the rough probability
for each reaction. They are listed below;

D+T --> (Helium at 3.5 MeV) + (Neutron at 14.1 MeV) 98.85%
D+D --> (Tritium at 1.01 MeV) + (Proton at 3.02 MeV) 0.30%
D+D --> (Helium3 at 0.82 MeV) + (Neutron at 2.45 MeV) 0.30%
T+T --> Helium + 2 neutrons + 11.3 MeV 0.20%
T+He3 --> Helium + Proton + Neutron + (12.1 MeV) 0.003%
T+He3 --> (Helium at 4.8 MeV) + (Deuterium at 9.5MeV) 0.003%
T+He3 --> (He at 0.5 MeV) + (N at 1.9 MeV) + (P at 11.9 MeV) 0.0004%
D+ He3 --> (Helium at 3.6 MeV) + (Proton at 14.7 MeV) 0.36%
He3 + He3 ---> (Helium) + 2 Protons +12.9 MeV ~zero

Lots of crazy stuff. It is from this model, we could assign energies
and start to estimate what a best case scenario would be for Bussards'
Polywell. Typically, extra high voltages for physics experiments are
about 345,000 volts. Where would that put us on the chart? If we
were attempting the pB11 reaction, we can figure it out letting the
proton be frozen in space and letting the boron crash into it. The
energy would be: (charge of 5 times 345,000 plus, a charge of one
times 345,000) or about 2.07 Million electron volts. We would be just
off this chart.


3. Neutron. Free neutrons are not normally stable, they have a
half life of about 15 minutes. However, in the Bussard reactor, they
are going to hit the chamber walls and make the metal (and the rings)
radioactive. With the 2.45 MeV of energy that they will have, they
will cook everything, heating it up.


4. Helium3. See above. This is the same Helium3 that everyone
talks about getting from the moon.



Sources:

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

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

http://en.wikipedia.org/wiki/Tritium-3

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

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

http://en.wikipedia.org/wiki/Electric_p ... ansmission

[D Tibbets]

I believe your proton reaction is wrong. A proton + electron +anti neutrino --> neutron. This is a three body reaction ( all three particles need to come together at the same time) and is therefor extremely rare.

In a Polywell any charged fusion products with speeds significantly above the potential well will not be electrostatically contained and so will leave the system before they can contribute much in the way of further fusion reactions. Bussard discussed this in one of his papers. I think he called it the 1/2 catalyzed D-He3 reaction. 2 D-D fusions results in 1 proton, 1 He3, 1 tritium, and 1 neutron. The tritium and He3 need to be pumped out of the vacuum vessel, processed and then fed back into the system as new fuel ions. The tritium might be diverted for other uses- such as Bets voltaic batteries. The process effectively doubles(?) the energy obtainable per parent deuterium fuel ion. Bussard and others also mentioned having Boron10 in the walls of the vacuum vessel to capture neutrons, Subsequent radioactive decay produces lithium and additional tritium (or is that He3?), along with some more heat. This increases further the total amount of energy that can be extracted from the original deuterium fuel.

Conditions where D-D fuses well will provide for easy D-T fusion, and so long as the potential well is near 100 KeV, the D-He3 reaction will also occur more rapidly than the D-D reaction.

One option that has been discussed some, if the P-B11 reaction cannot be made to work, would to collect the He3 produced from a D-D burning Polywell and store it for use in a mobile (like a ship) reactor where you are trying to minimize neutrons and use more efficient (and possibly lighter and more compact) direct conversion, instead of steam conversion. This would provide the fuel for these potentially smaller power plants without having to mine He3 from the Moon.

As far as determining the ideal potential well depth for the P=B11 reaction, it is complex. As discussed in a recent thread, the high Z (multiply ionized boron ions (up to +5) will gain more energy, so a smaller potential well is needed to reach a target energy. This is important because the losses from Bremsstrulung x-ray radiation goes up rapidly with temperature (eV). This advantage/ disadvantage of high Z fuels helps to determine whether P-B11 fusion can break even, when some other considerations of the Polywell is figured in (location of hot electrons). Dense Plasma Focus proposes another mechanism to overcome this Bremsstrulung barrier. I don't know how RFC systems are supposed to manage it.

D Tibbets

[MSimon]

Actually the calculation of reaction energy vs drive voltage is not hard:

http://iecfusiontech.blogspot.com/2007/ ... r-iec.html

http://iecfusiontech.blogspot.com/2007/ ... r-b11.html