reddit: We are nuclear fusion researchers, ask us anything

[Skipjack]

And I said that I could not found explanation how very small plasmoid can stop each other that is needed for merging. And, so, I do not believe in viability of this approach too.
Another issue if small plasmoid collides large volume of background plasma. In this case yes majority of kinetic energy transfers into thermal.

Did you actually bother reading up on the works by Slough, Rostoker and co, or where is the wisdom coming from? Another paper by Rider?

[Joseph Chikva]

And I said that I could not found explanation how very small plasmoid can stop each other that is needed for merging. And, so, I do not believe in viability of this approach too.
Another issue if small plasmoid collides large volume of background plasma. In this case yes majority of kinetic energy transfers into thermal.

Did you actually bother reading up on the works by Slough, Rostoker and co, or where is the wisdom coming from? Another paper by Rider?

Yes, I have read some of their works. Also I am aware with some Rostoker's patents.
And I declare that do not see any approach allowing to build fusion reactor with Q>1 in near years.
Somewhere here at this board I have calculated that for stopping of two small colliding plasmoids about 10000 N order force is required. Can you quote me any piece of mentioned by you works where such strong forces’ creation possibility is shown?

[Skipjack]

Did you read this paper also?
http://www.msnwllc.com/Nuclear_Fusion_IPA.pdf

Got a link to your calculations? Maybe you should share them with John Slough. I have heard that in contrast to Rostoker, he is quite approachable with questions and critique as well.

[happyjack27]

Regarding Todd Rider's thesis - he worked on both thermally-equilibrated and highly nonthermal distributions. The takeaway in either case: P-B11 fuel would bleed off a lot of its energy due to Bremmstrahlung losses, more in fact than it produces from fusion (by a factor of around 1.75, as I recall). A nonthermal distribution would reduce this factor, as a greater fraction of your distribution could actually fuse (in a thermal distribution, it's really just the high-energy "tail" of the Maxwellian that fuses), but it's still over-unity (something around 1.2 for P-B11). Add to that the requirement of energy input to maintain the nonthermal equilibrium, as the plasma will relax very quickly to a thermal distribution, and you run into problems. This effectively kills concepts like a polywell or fusor, which require active maintenance of the nonthermal distribution...

D Tibbets beat me to it: notice they are not considering ions and electrons separately here. they are assuming that the electrons are at about the same speed as the ions. and thus, yes, even in a monoenergetic distribution you'd have high Bremmstrahlung losses, because your electrons are fast. but this is not the case in a polywell. in a polywell your electrons are very slow in the fusion region, so the Bremmstrahlung losses would be much lower than both cases they're considering.

in sum, they consider two cases:

a) both electron and ions are thermal, at the same (high) temperature,
b) both electrons and ions are non-thermal, at the same (high) kinetic energy.

however, polywell is:

c) none of the above. ions and electrons are at different energy levels. namely, electrons are very slow while ions are very fast.

[Robthebob]

To learn that Rider started his paper with something so arrogant, meh...

[D Tibbets]

How to explain you that within the next 10 years Tokamak approach does not allow to build practical reactor?

Reread what I said. My point was that Toks will NOT be able to do it in 10 years, but IMHO FRC- colliding beam reactors will be possible within the same timeframe, provided they get enough funding. So you were lecturing me the very same thing that I said

And I said that I could not found explanation how very small plasmoid can stop each other that is needed for merging. And, so, I do not believe in viability of this approach too.
Another issue if small plasmoid collides large volume of background plasma. In this case yes majority of kinetic energy transfers into thermal.

I do not know much about FRC fusion, except that there seems to be two different approaches. A steady state and a pulsed mode. As far as two plasmoids, large or small stopping each other, I get the impression that that you think that the system is a one pass machine. I think they are actually a confinement scheme where the lifetime is enough for many orbits, so only a tiny fraction need to interact on each orbit. Due to various factors, Tokamaks need to keep the ions confined for possible interactions for many hundreds of seconds, Polywells for a few tens of milliseconds, DPF for less than a microsecond and FRC for ? seconds. It is not a matter of achiving high collision efficiencies alone, but the combination of fusion collision efficiency and confinement time and cost of the confinement per unit of time- the triple product.

Dan Tibbets

[Joseph Chikva]

As far as two plasmoids, large or small stopping each other, I get the impression that that you think that the system is a one pass machine. I think they are actually a confinement scheme where the lifetime is enough for many orbits,...

Dan Tibbets

Two plasmoids generated by plasma guns arranged oppositely at the same axis collide each other under influence of increasing by time axial magnetic field (something like theta-pinch in the merging zone of reactor).

[Joseph Chikva]

Did you read this paper also?
http://www.msnwllc.com/Nuclear_Fusion_IPA.pdf

Got a link to your calculations? Maybe you should share them with John Slough. I have heard that in contrast to Rostoker, he is quite approachable with questions and critique as well.

Despite to that there is written the following:

The merging and conversion of the FRC kinetic energy was observed to take place on the Alfvenic timescale. The distinct difference between merging and the simple passage of the FRC unopposed is clearly demonstrated in the array of excluded flux signals in the interaction chamber as illustrated in figure 4. The two FRCs merged as they collided to form a single FRC indicated by the peak diamagnetism appearing and remaining at the axial midplane. It is worth noting that with merging the excluded flux increased by a factor of at least four greater than observed for the transiting FRC.

I weakly believe in that. As I am repeating there is not written anywhere at the expence of what forces the stopping of plasmoids and consequently their merging is possible.
But picture above is very beautiful.

[MSimon]

The Tok boys are going to have to explain how their neutron economy is going to work. About 90+% of the neutrons generated have to be captured in the blanket. That is a very hard engineering nut to crack.

Costs can be papered over to some extent for now. Engineering practicality can not. IMO. YMMV.

[Joseph Chikva]

The Tok boys are going to have to explain how their neutron economy is going to work. About 90+% of the neutrons generated have to be captured in the blanket. That is a very hard engineering nut to crack.

Costs can be papered over to some extent for now. Engineering practicality can not. IMO. YMMV.

Blanket issue is only the secondary challenge, while neutron generation via fusion is the main.
All Tokamaks developers mean that blanket thickness of about 70 cm is enough for effective capturing of neutrons. And inevitable leakage of neutrons should be compensated by multiplying of neutrons with the help of beryllium or lead. Neutron multiplying rate is estimated as 1.15+ (fusion neutrons quantity x 1.15 or more)
If we are losing 10% of neutrons multiplication coefficient should be not less than 1.15/0.9=~1.28
And then additional 4.6 MeV via reaction n + Li6 will be effective for total energy balance.
And as I know several designs of blanket modules have been already developed and are ready for testing when ITER will start running.

[Skipjack]

Yes, but they will have to replace the very expensive components of ITER and future Tok- reactors frequently thanks to neutron damage. Sloughs FRC only has to replace the small burn chamber every now and then which is far enough away from the more expensive parts of the reactor. That makes it much more economic to operate.

[Joseph Chikva]

Yes, but they will have to replace the very expensive components of ITER and future Tok- reactors frequently thanks to neutron damage. Sloughs FRC only has to replace the small burn chamber every now and then which is far enough away from the more expensive parts of the reactor. That makes it much more economic to operate.

Let Slough first build his reactor, then let he achieve breakeven, then let's talk about blanket module's lifetime.
As neutron damage depends only on neutron flux. If you have powerful DT or DD or running on other neutronic fuel reactor, you will have neutron damage.
But doesn't the problem of neutron damage solve for fission reactors? Solved. And solved so successfully that today humanity has nuclear power plants (fission and neutronic) with 1 kW*h production cost compatible with largest HPP plants.
Neutron kinetic energy in fission reactors is higher than 14.1 MeV. Yes flux is lower at the same power. But it is solvable problem.
And if Slaugh's reactor will run at neutronic fuel and if that will work, that inevitably will have the same problems with neutron damage of materials as other neutronic fusion reactors.

[Skipjack]

Joseph, REREAD what I said!
The BURNCHAMBER will get damaged by neutrons, yes. But the expensive parts of the reator are NOT in the BURNCHAMBER.
They are at the ends, far away from it.
Also note that he has already built a 1/3 scale reactor which he has used to confirm almost all of his claims (and repeatably). All he has to do with the next bigger reactor is confirm the scaling to Q>1.

[Joseph Chikva]

Also note that he has already built a 1/3 scale reactor which he has used to confirm almost all of his claims (and repeatably).

Repeatably?
Who repeated?

Almost of his claims?
May be because of my bad English, but I understand the word "almost" as "not all" or "not entire". If so, some claims were confirmed and some were not. Which claims were not confirmed?

Now some points:
What do you think, does collision of galaxies mean the collision of stars belonging to them? I would answer that no. Probability of collision depends on number density, linear dimension of plasmoid and cross-section of stars. And on nothing else.
*number density - in the best case is 10^22 m^-3 (even cigarette smoke is denser)
*linear dimension of plasmoids - small
But Slaugh and his followers consider two colliding FRC as solids colliding in non-elastic manner stopping each other and their kinetic energy totally transfers to thermal. Is this the right model?

[Roger]

he may have considered both thermalized plasma and mono energetic plasma, he did not consider the energy distribution of the electrons.
Dan Tibbets

Dan if I may, in laymans terms, Rider showed us scenarios why Polywell wont work, he did not show us scenarios why Polywell would work...

No?