Lawaranceville E-Newsletter

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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Giorgio
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Location: China, Italy

Re: Lawaranceville E-Newsletter

Post by Giorgio »

Skipjack wrote:
Sat Mar 27, 2021 6:55 am
Helion is going to use a D+D -> He3 + D cycle. The T from the second D+D branch will eventually decay into more He3 too.
I have never been really convinced on this fuel cycle idea, that's why I said that they need to crack the technological barrier to fusion.

In D-D there is 50% of the fusion products that goes to Tritum + p, and the other 50% goes to 3He + n.
If you can't properly control this environment you have a soup of D,T,3He, p,n that can give rise to a plethora of side reaction that can cool down the plasma, lower the overall efficiency or even damage the machine/equipment.
That's why p-B11 would be the best route even if it is the hardest one to ignite.

Anyhow, we can only keep waiting (and lurking) to see what they will disclose in the future.
A society of dogmas is a dead society.

Skipjack
Posts: 6199
Joined: Sun Sep 28, 2008 2:29 pm

Re: Lawaranceville E-Newsletter

Post by Skipjack »

Giorgio wrote:
Sun Mar 28, 2021 11:06 pm
Skipjack wrote:
Sat Mar 27, 2021 6:55 am
Helion is going to use a D+D -> He3 + D cycle. The T from the second D+D branch will eventually decay into more He3 too.
I have never been really convinced on this fuel cycle idea, that's why I said that they need to crack the technological barrier to fusion.

In D-D there is 50% of the fusion products that goes to Tritum + p, and the other 50% goes to 3He + n.
If you can't properly control this environment you have a soup of D,T,3He, p,n that can give rise to a plethora of side reaction that can cool down the plasma, lower the overall efficiency or even damage the machine/equipment.
That's why p-B11 would be the best route even if it is the hardest one to ignite.

Anyhow, we can only keep waiting (and lurking) to see what they will disclose in the future.
Pulses reactors have an advantage there because they can remove the products between shots. The time is probably too short for any significant amount of the products to fuse in side reactions. Also, you can sort of control the environment to further reduce the likelihood of this happening. I think, they will be fine.

Giorgio
Posts: 2849
Joined: Wed Oct 07, 2009 6:15 pm
Location: China, Italy

Re: Lawaranceville E-Newsletter

Post by Giorgio »

Skipjack wrote:
Mon Mar 29, 2021 4:07 am
Pulses reactors have an advantage there because they can remove the products between shots. The time is probably too short for any significant amount of the products to fuse in side reactions. Also, you can sort of control the environment to further reduce the likelihood of this happening. I think, they will be fine.
Yes, I was mentioning in the other thread that I agree that the 2 Hz pulses operation is an advantage to limit impurities, but this will not solve the D-D fusion chain issue because anyhow 50% of the fusion products will take the Tritium route regardless of length of fusion (compression) time.
A society of dogmas is a dead society.

Skipjack
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Joined: Sun Sep 28, 2008 2:29 pm

Re: Lawaranceville E-Newsletter

Post by Skipjack »

Giorgio wrote:
Mon Mar 29, 2021 7:35 am
Yes, I was mentioning in the other thread that I agree that the 2 Hz pulses operation is an advantage to limit impurities, but this will not solve the D-D fusion chain issue because anyhow 50% of the fusion products will take the Tritium route regardless of length of fusion (compression) time.
I think you misunderstood me. The goal is to fuse D+D and make He3 and T. The T and He3 get separated and the He3 is fed back into the system for the next pulse. There won't be any T left in the reactor to fuse with a D in the next shot. That is at least what I understand to be the goal.
Now there is of course a possibility that the T will fuse with a D right after it was produced in the same shot. I think that largely depends on the fuel mix. If they run it He3 rich, the chances are lower, though that might cause the problem that you consume more He3 from He3 + He3 and D+He3 reactions than you produce from D+D reactions. I am not entirely sure how high the chances for these D+T reactions are but from what I know and understand I would put the likelihood of this in Helion's reactor at around 5%, most likely a lot less. That is because the Tritium will be very energetic (1 MeV), in a 40keV plasma. AFAIK, it would have to slow down considerably before it can fuse with a D. So we would first have to produce a T from a D+D reaction (50% chance). That T then has to hit a D, rather than a He3, or a p and both are present in the plasma 50% * 0.333 and then it has to slow down significantly before the pulse is over. Not sure about that chance, but I would be surprised if it was more than 30%. Ah and let's not forget that the 50% chance of a tritium being produced is a relatively high estimate, since there are also D+He3 reactions (though again those depend on the fuel mix).
But don't take my word for it. I am not a plasma physicist and may be off in my estimate somewhere.

Now the T is an interesting thing actually. You could store it until it decays into more He3, or you could sell it and make a lot of money. Tritium is (at least right now) more than an order of magnitude more expensive than He3. So one could sell the T and buy more He3 and still have money left in the bank. Question is how long that will go before the market is saturated with T and higher demand drives up prices for He3.

Giorgio
Posts: 2849
Joined: Wed Oct 07, 2009 6:15 pm
Location: China, Italy

Re: Lawaranceville E-Newsletter

Post by Giorgio »

Skipjack wrote:
Mon Mar 29, 2021 9:28 am
I think you misunderstood me. The goal is to fuse D+D and make He3 and T. The T and He3 get separated and the He3 is fed back into the system for the next pulse. There won't be any T left in the reactor to fuse with a D in the next shot. That is at least what I understand to be the goal.
Yes, I also mean that the chamber will be completely evacuated before next shot and than (according the patent) some of the 3He recovered from the decay of Tritium will be re-injected into the reactor. The patent makes some very optimistic assumptions on the fuel cycle they intend to use, so when I speak of "solving the D-D fusion chain", I mean to find the correct parameters (if possible) to push the reaction toward the right path while avoiding as much as possible all the side fusion that are negative to the energy balance.
A society of dogmas is a dead society.

Skipjack
Posts: 6199
Joined: Sun Sep 28, 2008 2:29 pm

Re: Lawaranceville E-Newsletter

Post by Skipjack »

I think the most likely undesirable side reaction will be D+T and I don't think chances of that are that high.
I did some more digging and it looks like my above estimate of (max) 5% was pretty good:
The levitating D- Pole experiment assumed a probability for D+T side reactions in a He3 catalyzed D+D reactor at 7%, but that is with a (to my understanding) steady state design (that will have more trouble getting rid of the products), not a pulsed design. I would assume that the probability in a pulsed reactor was a lot lower than that.
https://www-internal.psfc.mit.edu/ldx/p ... ldr_v5.pdf

Giorgio
Posts: 2849
Joined: Wed Oct 07, 2009 6:15 pm
Location: China, Italy

Re: Lawaranceville E-Newsletter

Post by Giorgio »

Skipjack wrote:
Mon Mar 29, 2021 10:27 am
I think the most likely undesirable side reaction will be D+T and I don't think chances of that are that high.
I did some more digging and it looks like my above estimate of (max) 5% was pretty good:
The levitating D- Pole experiment assumed a probability for D+T side reactions in a He3 catalyzed D+D reactor at 7%, but that is with a (to my understanding) steady state design (that will have more trouble getting rid of the products), not a pulsed design. I would assume that the probability in a pulsed reactor was a lot lower than that.
https://www-internal.psfc.mit.edu/ldx/p ... ldr_v5.pdf
Interesting paper.
I gave it a quick read, but the assumptions they make to reach their conclusion cannot be applied on a FRC machine, especially for what it relates to the MHD stability requirements. in a FRC machine the compression phase could/should increase the side reaction fusions like the D-T one.
Than again, is not something i can be sure of, so we will need to wait some real experiments.
A society of dogmas is a dead society.

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