EMC2 news

[Skipjack]

Are you or have employed by John Slough or Helion? Have you been directly involved with the work they are doing? Have you at least been in the lab and talked serious science with the PI?

I too "have knowledge that I don't share here."

I say this because I DO know first hand that others of equal or greater stature do not see him the way that you do.

I guess it depends on who you talk to. This is academia in a highly competitive and very complicated field full of people that are very entitled to their opinion. One of my friends is the senior scientist at ITER, probably the most mainstream fusion effort you can find. Yet, ITER is probably among the most harshly criticized projects in the field (due to the delays and cost overruns) and his person is most likely not uncontroversial among ITER's detractors.
Finally, I want to add that clearly not everyone around Slough has a low opinion of him or his work (personally I know more people that like and respect him than the other way round). In example Charles Grossnickle, who lead the other (steady state/He3) FRC effort at the UW before his lab ran out of funding, always talked about Slough and his research with lots of respect and as I mentioned earlier Michl Binderbauer from TAE also seemed to be rather fond of him.

I personally have not spoken or interacted directly with any of the core Helion team.

I think you should do that, when you have the opportunity. It would be a good idea to actually get some first hand information prior to forming an opinion and then expressing that opinion rather viciously on a public forum. You know that you can actually hurt peoples serious and honest efforts this way.

You have missed the point. Slough is a high density plasma guy. What I have been asking you is who are the other high end plasma guys? Why are there not any?
Kirtley is not a high density plasma guy, he is a plasma jet guy, and did not spend that long doing it. He is not considered a top tier plasma scientist in the community.

You asked for careers outside of MSNW, I showed you careers outside of MSNW. So it is you who missed my point. David Kirtley is most of all an engineer with a lot of experience of managing projects similar to this, which is one reason why he is holding the position of CEO at Helion.

So again, if Slough is at the front of the argument for succeeding in compact plasma based fusion, why is there not another top tier guy on his team? One would think that folks would be lining up.

Money? High end plasma physics people cost a lot of money and Helion have not exactly been blessed with tons of funding until very recently. Helion is hiring right now but I do not know what kind of people they are looking for. From what I understand most of their remaining issues are more related to systems engineering than the fundamental plasma science.

These guys do talk to each other all the time, and they do know who is doing what and how. There is an completely formed and functioning layer under these public marketing displays that you are apparently unaware of where the senior folks in the community are constantly having interaction. You can almost call it the unofficial "Plasma Fusion Science Board". And yes, I do know and talk to folks in that circle.

Once again, you are making assumptions about my person and what or who I know or don't know.

Art Carlson once tried to label Eric Learner's work as bad science. He eventually abandoned the effort for what ever reason. LLP has since demonstrated significant results and insights. That does not mean his efforts will suceed from a physics standpoint or engineering standpoint, but it is promising.

I have a lot of respect for Art. He is/was one of the more knowledgeable people to post on this board. I cant remember what exactly he said about LPP. I do understand his skepticism however. I find them rather likeable (maybe a bit quirky, but who isn't?) and I am watching them with a lot of interest because of their open approach but I am still not convinced that their efforts will go anywhere in the end. From my understanding a big problem with their concept is that it does not scale well. If they can't make it work at the current scale with enough Q to be feasible, they will be stuck. And a lot of that depends on whether they can get the direct conversion to work.
I once again find it worth pointing out that Art originally was also highly skeptical about Helion and Slough but changed his mind after visiting their lab. So if people don't take it from me (because I am just a software engineer), you should at least listen to Art.

35 KeV seems low, for D-He3, I would expect target temperatures closer to ~ 80 KeV. 35 KeV would be good for D-T, poor for D-D, but bordering on dismal for D-He3 (based on viewing cross section grafts and corresponding Bremsstruhlung rates. Bussard pointed out in one paper that about 5 KeV was the absolute minimum for D-T fusion output yield to exceed Bremsstruhlung losses, even with assumed perfect particle confinement. Other fuels have higher minimal (and for that matter maximum) temperatures for the window where fusion output can exceed Bremsstruhlung losses.

I honestly don't have a good answer for you, right now. It may be that they use the 35keV number only as a requirement for their upcoming break even experiment and not for the actual economic power generating reactor. I cant say that with confidence right now, however.

The comment about persueing D-T as an admission of inferiority is an uncertain assessment.

I did not mean it that way. I meant that it is an easier goal to reach and I know that EMC2 is going to do that for the first version of the Polywell. Where they will go from that remains to be seen and probably depends on the results of their experiments. My main point was that due to the geometry and layout of the Helion reactor, it is comparably well suited for D+T since it is comparably easy to service. I find it worth mentioning that they already have 5 keV, which as you say is enough heating power for D+T (even though it may be the bare minimum).
This would theoretically allow Helion to go with D+T as a fallback for an actual commercial reactor, not just for an experimental reactor.
I may be wrong (please correct me if I am), but I don't believe the Polywell is as well suited for D+T. LPP's DPF certainly is not. TAE's reactor is much more complex with lots of expensive parts near the central "burn" chamber. So I assume (but may be wrong) that it won't work as well for D+T.

For aneutronic fusion the Polywell has some tricks that may benefit it. I don't know how the FRC handles these issues (as well). Spherical convergence, and energy distribution of electrons associated with an electrostatic potential well are significant advantages. Could some of these electrostatic considerations be applied to FRC?

I agree with the advantages of the Polywell for PB11. But then, we also have TAE who are convinced that their FRC machine will work well with PB11. Their design is aiming for a steady state with long confinement times, measured in minutes, however.
Helion's reactor has some similarities to TAEs design, but because they are less ambitious and more pragmatic, they have lower requirements that are easier to meet. This IMHO gives them a lot of credibility, but your own impression may differ. Anyway, I don't think I came over as talking down on Dr Park or the Polywell or anyone for that matter. If I did, it was not on purpose. I simply think that with the current funding situation and goals set for each effort that I am watching, Helion has IMHO the best shot at being first. The future is hard to predict and I might very well be wrong.
I did not expect this to turn into a mud fight over the reputations of the people involved, which I honestly find highly inappropriate.
I really like Dan's factual argumentation (thanks, Dan) and will try to get some answers for him, if I have the chance.

[D Tibbets]

D-T fusion is for the timid . At least that is my bias. I don't know why Parks promoted this fuel for the Polywell, asside from my speculation. From the start, D-D fusion has always been the Polywells basic target. From an intermediate experimental setup perspective, the problems with handling tritium is significant. D-D is a much easier approach from an experimental/ engineering perspective. If fusion power by measuring neutron output is your metric, D-D is just as good, if not superior. Less shielding, easier thermalization of the neutrons, etc. As with the Japanese Tokamak, burning D-D fuel gave (I think) good measurements that can be directly extrapolated to D-T fuel predictions. Money and time is saved with this approach and I suspect that money and time will remain the major challenge for any of the projects pursuing useful fusion technology. This even applies to ITER, though on a much larger scale.

I agree that the Polywell may be a poor choice for D-T fusion. The internal magnets would be exposed to a lot of neutron bombardment. Note though that the Lockheed design has similar magnet exposure, and liquid salt cooling is proposed to handle the neutron flux. With tritium breading requirements I assume the metal in the liquid metal salt would be mostly lithium. Conversely, the X ray exposure in a D-T machine will be less, perhaps much less when considering aneutronic alternatives. This was Riders contention. I remain unconvinced of D-T viability, not so much due to triple product considerations, but due to the tritium breeding challenges and the mostly unexplored diverter technology. I wonder how much a pulsed approach (of a few milliseconds) in a FRC or other ignition (ie: thermalized) machine relaxes the challenges of the diverter. I understand it will be a major concern for the Tri Alpha FRC.

Concerning Art Carlson's efforts against Eric Learner, my understanding was that mostly it was directed towards the LPP Wikipedia page. He actually managed to ban Learner from editing the page, which was ironic. considering it was his project. He criticized R. Nebel on a physics forum, and after some back and forth the debate shifted to Talkpolywell, where the arguments and counter arguments continued for a time. Whatever Art Carlson's motives were, the back and forth was enlightening and educational. The openness of R. Nebel was also refreshing, I wish it had continued.

Dan Tibbets

[Skipjack]

Got some answers for you, Dan

35 KeV seems low, for D-He3, I would expect target temperatures closer to ~ 80 KeV. 35 KeV would be good for D-T, poor for D-D, but bordering on dismal for D-He3 (based on viewing cross section grafts and corresponding Bremsstruhlung rates.

You are correct. The D-He3 ion temperature which maximizes gain is around 80 keV (some models say 70, some say 100 keV). System scale and complexity increase with required heating and temperature. Helion's models say that on a system level, it is better to run at a lower (but not too low) temperature. 35 keV is the absolute minimum temperature. That said, no one, including them, has operated a Helium 3 compact toroid at 30+ keV experimentally yet, so these still heavily theoretical numbers and have to be treated as such.
There is quite a bit of literature on steady Helium 3 systems, less on pulsed Helium 3, and little reliable data.

In any case with a few millisecond confinement time the density has to be high , probably above 10^22/ M^3 for useful amounts of fusion to occur in these small machines. Both triple product considerations and practical power output considerations are important.

FRC plasmas routinely operate at densities greater than 10^22 and all lifetime scaling must reflect a density component. 10^23 to 10^24 densities are commonplace. For reference, the entire ARPA-E fusion program is based on pulsed fusion plasmas at 10^24 and greater densities as they believe there is an economic optimal.
Lot’s of good references in Section B in here as well:
https://arpa-e-foa.energy.gov/FileConte ... 9f3d3fec53

D-T fusion is for the timid . At least that is my bias. I don't know why Parks promoted this fuel for the Polywell, asside from my speculation. From the start, D-D fusion has always been the Polywells basic target. From an intermediate experimental setup perspective, the problems with handling tritium is significant. D-D is a much easier approach from an experimental/ engineering perspective. If fusion power by measuring neutron output is your metric, D-D is just as good, if not superior. Less shielding, easier thermalization of the neutrons, etc.

I agree with you on that

I agree that the Polywell may be a poor choice for D-T fusion. The internal magnets would be exposed to a lot of neutron bombardment.

Which was the point I was trying to make earlier. The more interesting is Parks choice to go with D+T for a first reactor. I still don't understand that. Is he just trying to minimize risk to increase attractiveness for investors?

Note though that the Lockheed design has similar magnet exposure, and liquid salt cooling is proposed to handle the neutron flux. With tritium breading requirements I assume the metal in the liquid metal salt would be mostly lithium. Conversely, the X ray exposure in a D-T machine will be less, perhaps much less when considering aneutronic alternatives. This was Riders contention.

I think the biggest problem with D+T and tritium breeding is that the reactor geometry has to be such that the neutrons are optimally captured by the lithium blanket to achieve good heat transport and tritium breeding. This is one of those things where I think that Helion's reactor has an advantage over others. The majority of the neutrons are concentrated within a relatively small cylindrical section in the middle of the reactor. No complex equipment exposed to the neutrons and a comparably simple geometry for the lithium blanket.

Whatever Art Carlson's motives were, the back and forth was enlightening and educational. The openness of R. Nebel was also refreshing, I wish it had continued.

Me too. To bad Art got fed up and left the forum, as did a few others

[mvanwink5]

With plasmas, real world machines and well designed experiments settle the arguments, and Park's proof on Grad's cusp plugging theory put to rest the major arguments against Polywell. Until then, it was a lot of postulating. Now, the $30M machine is needed to finish settling the remaining arguments. I am sure Art is happy with positive results even though he was dubious.

[alexjrgreen]

ITER will procure the tritium "fuel" necessary for its expected 20-year lifetime from the global inventory. But for DEMO, the next step on the way to commercial fusion power, about 300g of tritium will be required per day to produce 800 MW of electrical power. No sufficient external source of tritium exists for fusion energy development beyond ITER, making the successful development of tritium breeding essential for the future of fusion energy.

Tritium production looks like a licence to print money. When I spoke to Tokamak Energy at the Royal Society's Summer Science Exhibition, they were also talking about D-T and a Lithium blanket to breed more.

[crowberry]

Anyone hear anything more about Sandia Labs Z Pinch, there was talk of a breakeven shot a year or two back?

The only news I have noticed is in this post viewtopic.php?f=6&t=5556#p122219.
There are quite a few talks on MagLIF at the upcoming 57th Annual Meeting of the APS Division of Plasma Physics. This is just one example abstract: http://meetings.aps.org/Meeting/DPP15/Session/JO6.7.

[ladajo]

expressing that opinion rather viciously on a public forum

Are you saying that is what I did?
If so, you are reading way too much into it and that should be a cue for you to review your internal biases and ability to separate objective from subjective constructs.

Since you are so focused on expressing you worldly knowledge on nuclear physics and engineering lets just focus on that for a moment.




This is why one picks D-T over D-D in an entry level demonstration machine. This is why 5KeV is the normal min. target for a machine, because it is the lowest round number that should produce some measure of reactions. 10KeV gives you almost two orders of magnitude increase in the reaction probability. So that is typically the next level of engineering target. Fundamentally, a research machine does not care what the fuel is. It does not matter. What matters is that what ever fuel you put in it, the reaction probability for the CoM is sufficient to produce detectable results. It is simply mind-boggling to me that you are even having the above debate over fuel.
If the design can not achieve a KeV over time sufficient then the dreaming of what a production machine would look like is completely irrelevant. This is the part that is lost on you and others as part of an assessment of who is closest to the target.
The engineering of a machine to meet EPRI fusion reactor based generation plant criteria (you remember, the guys that you said don't matter) is beyond the fundamental discussion on the table today, which is "will it work". The ONLY design that is perceived to meet "will it work" criteria is ITER. But it is NOT proven, thus they are building ITER.
If ITER works like it is perceived it will, THEN the next step is to build DEMO, which is a first attempt at the EPRI criteria for a functional fusion power plant. That said, it is widely assessed that TOKAMAK designs as we understand them and have the physical capability to construct them given known technology levels (for the most part, cause some requirements for ITER are not actually technically feasible yet, ergo rolling timeline), that a TOKAMAK design will never adequately satisfy the EPRI criteria to be a viable plant.

So now, back to compact designs. Professing that one design is better than another from a sustainability standpoint is completely foolish until we have a much more developed sense of "will it work". Stressing over materials and neutron flux issues, gamma flux, alpha pitting or whatever is just a waste of time at this point.
What is most important is "WILL IT WORK?"
And to date, no research effort has shown that. Some can be argued to be closer, and some can be argued to be further. That is also relatively moot, because when in the world of research, especially a cutting edge (ie. folks didn't go there yet) field, there are many surprises, both positive and negative. If you have a magic ball, and can predict what we don't know we don't know, then you should be in charge of the world. I am going to assume you don't have said magic ball based on your continued profession as a programmer and partaking of this forum on a regular basis.
The best assessment model that I believe can be employed yet is consideration of each research effort from both the accumulated knowledge of what isn't going to work as well as what helps it work compared to the other projects.
Given that EMC2 has advanced their work to the point the NEXT experiment is assessed to be the make or break point, ie. it will indicate viability or there is nothing left to try in the paradigm of known knowledge, I think that there is a strong argument when compared to other efforts that EMC2 has accumulated a large comparative pile of knowledge in understanding the hypothesis as valid or false, and could be considered closer to success.
The single question left for Polywell is the efficiency of the electron injection. And that can only be determined by scaling up the machine. It will be good enough, OR it will not be. If not, there is nothing else left to try and Polywell, given the current body of physics knowledge will be proven a false hypothesis. Otherwise, it becomes and engineering problem. The choice of fuel does not matter. If it can burn D-T at Q>1, but not D-D, then who cares, you engineer a D-T Plant that satisfies the EPRI criteria and off to the races.
If it works REALLY well, then you get to climb the fuel ladder, and engineering becomes easier in some aspects, but harder in others. You are still seeking to be viable per the criteria.
Oh, by the way, D-D also has D-T in the decay chain, which is in sufficient quantities and energies that it is a factor.
Also, where do you think you are going to source 3He as fuel?

[Skipjack]

This is why one picks D-T over D-D in an entry level demonstration machine. This is why 5KeV is the normal min. target for a machine, because it is the lowest round number that should produce some measure of reactions. 10KeV gives you almost two orders of magnitude increase in the reaction probability. So that is typically the next level of engineering target. Fundamentally, a research machine does not care what the fuel is. It does not matter. What matters is that what ever fuel you put in it, the reaction probability for the CoM is sufficient to produce detectable results.

I think everyone here is sufficiently aware of cross sections. Dan and I are already way ahead of you in this discussion.

The engineering of a machine to meet EPRI fusion reactor based generation plant criteria (you remember, the guys that you said don't matter) is beyond the fundamental discussion on the table today, which is "will it work". The ONLY design that is perceived to meet "will it work" criteria is ITER. But it is NOT proven, thus they are building ITER.
If ITER works like it is perceived it will, THEN the next step is to build DEMO, which is a first attempt at the EPRI criteria for a functional fusion power plant. That said, it is widely assessed that TOKAMAK designs as we understand them and have the physical capability to construct them given known technology levels (for the most part, cause some requirements for ITER are not actually technically feasible yet, ergo rolling timeline), that a TOKAMAK design will never adequately satisfy the EPRI criteria to be a viable plant.

Yes, yes we are all aware of ITER and Tokamaks and all the problems... Again, we are way ahead of you in the discussion.

Given that EMC2 has advanced their work to the point the NEXT experiment is assessed to be the make or break point, ie. it will indicate viability or there is nothing left to try in the paradigm of known knowledge, I think that there is a strong argument when compared to other efforts that EMC2 has accumulated a large comparative pile of knowledge in understanding the hypothesis as valid or false, and could be considered closer to success.

Helions next experiment is also aiming for break even (as I mentioned they already have the necessary temperatures for D+T but they are going for D+he3). I also want to point out that JET is currently getting refit for a break even D+T experiment. They expect to have that complete in the next couple of years IIRC. Several others are also claiming similar time frames. How credible they are remains to be seen. My point is that there are several teams that have made good progress and that have a better funding situation right now.

The single question left for Polywell is the efficiency of the electron injection. And that can only be determined by scaling up the machine. It will be good enough, OR it will not be. If not, there is nothing else left to try and Polywell, given the current body of physics knowledge will be proven a false hypothesis. Otherwise, it becomes and engineering problem. The choice of fuel does not matter. If it can burn D-T at Q>1, but not D-D, then who cares, you engineer a D-T Plant that satisfies the EPRI criteria and off to the races.
If it works REALLY well, then you get to climb the fuel ladder, and engineering becomes easier in some aspects, but harder in others. You are still seeking to be viable per the criteria.

Which is what we were discussing. The problem is that the internal geometry of a Polywell is not as suitable for D+T because of the magnets that are exposed to the neutron flux and IMHO you have limited space for shielding inside the machine too. As Dan and I speculated, D+T might just be Parks choice for the purpose of demonstrating that it can be done, then moving on to the next higher level fuel.

Oh, by the way, D-D also has D-T in the decay chain, which is in sufficient quantities and energies that it is a factor.

Yes, tritium catalyzed deuterium (TCD) fusion is a good option, if you can fuse D+D well enough. It is something Helion could do as well and I believe it popped up in some article about them at some point, but they are rather going the other way, which answers your next question...

Also, where do you think you are going to source 3He as fuel?

... the second branch of the D+D fusion reaction produces a He3 atom. Half of the Tritium from the first branch will beta decay into another He3 within 12 years or so. So this is where the He3 comes from. I thought I had mentioned this on this board before, but it might have been somewhere else...
Anyway, Helion is currently keeping the exact way they are doing the He3 fuel cycle under wraps.
There are several options that I see how they can do it. These are just pure speculation on my part:

1. Have a dedicated D+D reactor that does not really produce net energy but just produces He3 and Tritium as fuel for other dedicated reactors. You might be able to sell the Tritium for profit as well. It is in high demand.
2. Have a single reactor that alternates/cycles between D+D and D+He3 pulses.
3. It could be that they are planning to tune the fuel mix in a way that a single pulse will produce enough He3 for the next shot. I presume that in this case the mix would contain a lot more D2 and a lot less He3. So I guess one could regard it as a kind of He3 boosted Deuterium fusion, which would be the other counterpart to the Tritium Catalyzed Deuterium fusion you mentioned above.

It could be that they are going to implement it in stages. I presume (and again this is again just plain speculation) that having a dedicated D+D and a dedicated D+He3 reactor is easier because you can fully optimize each reactor for the fuel of choice (including shielding, product/fuel separation, etc).

[ladajo]

Dan and I are already way ahead of you in this discussion

Not really, but you go ahead and keep thinking that.

Helions next experiment is also aiming for break even (as I mentioned they already have the necessary temperatures for D+T

Empty statement. Tom Ligon has it in his garage as well. Seen it myself. And everyone's "next" try is aiming for breakeven. The only one NOT saying that is EMC2.
Maybe you should think about why.

The problem is that the internal geometry of a Polywell is not as suitable for D+T because of the magnets that are exposed to the neutron flux and IMHO you have limited space for shielding inside the machine too.

You don't actually know what you are talking about here. This is not an issue, and you have yet to present any accurately based argument on why it might be.. And it is no different for D-D or any fuel. What makes a difference, down the road, in an operating machine is energy collection strategies based on fuel. Every fuel has flux and material issues associated with it. "Internal Shielding", now that makes me laugh. It shows that you really have no understanding of fission/fusion core engineering. Given the cube function of flux generation, you don't shield within or immediately around the reaction volumes, there is no point to try. You mitigate. I can tell you have had no serious education on the principles employed for core volume designs involving nuclear reactions. Mitigation strategies involve many complex principles which at your level of displayed understanding involve primarily geometries and material choices. Again, a very basic take, but core volume and support structure design is an elegant dance of the applications of various principles to (ironically) meet criteria like EPRI's. ie. Make it a viable plant in a resourcing to product to market balance. Shielding in the volume...hehe...you don't have that many fingers dutch boy.

Half of the Tritium from the first branch will beta decay into another He3 within 12 years

And how do you store it? I think you will find the economics of that unviable. The amount produced verses your ability to collect whatevers left, and then store it. Right. Show me the numbers. Tritium is one of the hardest materials we know to 'put in a jar on the shelf' for later use. There is not enough made nor the ability to maintain it to terrestrially source 3He in sufficient quantities. You have some gaps in your logic chain. Here I'll even provide you a basic equation to do your analysis on:
3He avail from T sourcing = (T reactor production rate - T reactor burn rate - T reactor capture efficiency rate - T transfer to storage eff. rate - T storage leakage rate + T decay to 3He rate - 3He separation eff. rate - 3He transfer and storage efficiency rate) * Time period of effort
There are some other factors I am leaving out but this is a good starting point as it covers the most probable factors.
The operation of a reactor dedicated to 3He production at the beginning (be it a full time unit, or a switch mode 50% unit) means that you have right from the start cut in half your viability. Maybe that escaped you. I think you will find that the build / cost / operations balance estimates for existing approaches is not robust enough to support an effective doubling of required plant resources for a (even at best or if possible) 50% fuel production source. This also completely leaves out any consideration of a mass volume requirement analysis to find the resourcing verses demand balance point which it does not appear you have done.
So how many plants would you need to produce sufficient 3He fuel for a single 1GW 3He plant for a year of operations?
And, how much would that cost in relation to what you can sell the 1GW for?

[D Tibbets]

Dumping tritium into a reaction chamber is easy, essentially no different than deuterium. The problems with tritium is the regulatory and management loop holes you have to go through to handle it. Exhausting the reactor contents also,requires careful management of the unburned tritium. I suspect just diluting it may be inadequate, you would need to sequester it. This would probably be a very small part of the budget for an ITER scaled experiment, but for these smaller efforts clawing for barely adequate funding, the issue is not trivial. Handling the highly energetic D-T produced neutrons is defiantly, probably, possibly ( ) a major issue for any production reactor. I suspect the damaging and heating effects on superconductors may be the biggest issue. Materials management may mitigate induced radiation in the structure, but to keep the superconductors cold and durable, thicker first wall shielding is required. As, admitted, this may be countered at least in part due to the less X-rays at the colder D-T fusion temperatures. For a production machine that has to meet durability goals, it is another level of development. Well, sort of, deuterium- deuterium fusion is not exactly neutron free. In a Polywell or Lockheed type cusp machine though, only about 1/2 of the KE is carried by the neutron, and the total is less per reaction (works both ways in the arguement). The charged He3 and tritium produced would exit through the cusps so this component bypasses the magnet cans- significantly less cooling concerns for themagnets. All of this applies mostly to a production machine.

Admittedly, in a research, relatively low power machine, these issues are perhaps much less significant. And, the psychological impact of achieving real breakeven is much more convincing than projected breakeven based on D-D fusion results. The Japanese Tokamak reached breakeven with projected D-T fusion, based on their D-D fusion results, but publically at least, it is only a side note... I have no idea how much it contributed to ITER decision making.

My vision for a minimal useful terrestrial fusion industry is D-D fusion for main grid supply. This might be boosted by recycling the produced tritium ( part of the 1/2 catalyzed reaction) and B10 neutron capture boosting. But high efficiency tritium production requirements are avoided, no additional lithium first wall technology needed for development. D-He fueled reactors would be reserved for mobile low neutron producing reactors like in ships or spacecraft. Obviously, the grid D-D reactors would have to far exceed the mobile aneutronic reactors in total power production in order to provide the needed He3. Of course, P-B11 fusion , if possible, changes the entire game. But, this is a goal that probably needs to be pursued after viability of easier practical fuels is achieved.

There are only two reasons to pursue D-T reactions in my mind , the aforementioned psychological effects / bragging rights, and a high level of confidence that your system will only work with this easiest fuel.
My bias is that the highly preferred goal should be a minimum of D-D fusion. D-T is highly suspicious option, in my mind at least, when talking about an economically viable, useful power production industry.

As for profitable fusion, the baseline is not really D-T fusion, but Solar fusion. Here the physics are solved, the engineering is free for the basic reactor. Here the issues are the conversion of the delivered power into electricity or other forms of useful energy, and of course the constancy of the supply. Solar panels, Wind, even fossil fuels or biodiesel are simply conversions of this Solar fusion power. Cost, very long term aviability, and constancy of supply are the issues that determines if a system is actually useful. Fusion is here and proven, as demonstrated by the Sun. Other than Scientific curiosity , pursuing terrestrial fusion should be governed by the above goals. I feel that D-T fusion, at least along the ITER Tokamak path is a dead end. I am much less certain if alternate D-T fusion approaches are viable. My point is that if there is reasonable expectation that at least D-D fusion can be made to work in a machine, then it is reasonable to bypass the headaches (both large and small) associated with D-T fusion. The politics and perceptions are the primary advantages of persuing D-T fusion, not the end goals of a useful industry. This is based on my profound and unassailable expertise (cough... .

Dan Tibbets

[paperburn1]

I'm sure the whole reason why they are going with a DT machine is purely political. Once they show that they are capable of producing excess energy with their DT machine. All they have to do is make the simple statement if I had more money I could make even more energy to sell at a profit. Investors lined up around the block waving their checks and screaming take my money. And I'm sure Jay Park is a very smart man and when he builds his demo machine to be very easily able to be retrofitted into a DD machine or even possibly a D PB 11
but before any of the suitors even get that far they need to show that they can produce excess power. And in the money will pour it as this is a classic example of first past the post technology. It will not matter if somebody has a better idea or a better machine because in the short-term the person that produces excess power will get all the funding.

[Skipjack]

And it is no different for D-D or any fuel.

2.5 MeV (D+D) versus 14.1 MeV (D+T)? There is a reason why most experimental reactors are using D+D instead of D+T. A polywell has magnets inside and the whole reactor chamber is big. You need to surround all that with a lithium blanket in order to
A) convert as many neutrons as possible to heat for a steam cycle
B) breed tritium for fuel. Figuring out how to fit a lithium blanket neatly around a complex reactor geometry is one of the main issues ITER has had.
And you want to have some material protecting your reactor wall and magnets from the fast neutrons or you will end up with a maintenance nightmare.

Half of the Tritium from the first branch will beta decay into another He3 within 12 years

And how do you store it? I think you will find the economics of that unviable. The amount produced verses your ability to collect whatevers left, and then store it. Right. Show me the numbers. Tritium is one of the hardest materials we know to 'put in a jar on the shelf' for later use. There is not enough made nor the ability to maintain it to terrestrially source 3He in sufficient quantities. You have some gaps in your logic chain. Here I'll even provide you a basic equation to do your analysis on:
3He avail from T sourcing = (T reactor production rate - T reactor burn rate - T reactor capture efficiency rate - T transfer to storage eff. rate - T storage leakage rate + T decay to 3He rate - 3He separation eff. rate - 3He transfer and storage efficiency rate) * Time period of effort

You are right with that. Storing tritium is indeed an issue. That is why I said that it might be more viable to just sell the Tritium off. There is a very solid market for that. Though I am sure that the tritium storage problem is not completely unsolvable, if it is a necessity for the business case to close (and I am not saying that it is). I was speculating with that anyway (as I said).

The operation of a reactor dedicated to 3He production at the beginning (be it a full time unit, or a switch mode 50% unit) means that you have right from the start cut in half your viability. Maybe that escaped you. I think you will find that the build / cost / operations balance estimates for existing approaches is not robust enough to support an effective doubling of required plant resources for a (even at best or if possible) 50% fuel production source. This also completely leaves out any consideration of a mass volume requirement analysis to find the resourcing verses demand balance point which it does not appear you have done.
So how many plants would you need to produce sufficient 3He fuel for a single 1GW 3He plant for a year of operations?
And, how much would that cost in relation to what you can sell the 1GW for?

A pure D+D reactor would of course also produce some excess power that can be converted and sold (even more if you feed some of the Tritium back in for TCD). It is just not as economic and compact as a D+He3 plant. The D+He3 reaction releases a lot more energy and it is easier to extract since you do not need a steam cycle which you will most likely need to extract enough energy from a pure D+D plant in order to convert enough of the released energy (even more so if you do TCD).

How many D+D reactions you would need for the D+He3 reactions depends on too many factors that I currently do not know enough about and Helion is rather tight lipped about some of these details which they consider proprietary.
As I said earlier, it may just as well be that they are doing everything in a single reactor and just choose a very well tuned fuel mix (similar to what you suggested with TCD) and the possibility of separate reactors was just pure speculation on my side.

Let me add that so far none of the reactor concepts out there have proven that they will be economically viable. There are a lot of ifs for each and every one of them. This is one concept that has a good chance to close from a business POV.

Handling the highly energetic D-T produced neutrons is defiantly, probably, possibly ( ) a major issue for any production reactor.

Which is what I think as well. As I said, Helions reactor has the advantage that they "burn chamber" is a relatively small cylindrical section without complex and expensive equipment that needs to be protected and or replaced. This is why they originally proposed a D+T reactor (which is easier to achieve). But they are now confident enough that they can do D+He3).

Admittedly, in a research, relatively low power machine, these issues are perhaps much less significant. And, the psychological impact of achieving real breakeven is much more convincing than projected breakeven based on D-D fusion results. The Japanese Tokamak reached breakeven with projected D-T fusion, based on their D-D fusion results, but publically at least, it is only a side note... I have no idea how much it contributed to ITER decision making.

Yes and IIRC, so did JET. I think both did indeed have an impact on ITER, especially JET. Some of the highest positions at ITER are held by former JET people.

My vision for a minimal useful terrestrial fusion industry is D-D fusion for main grid supply. This might be boosted by recycling the produced tritium ( part of the 1/2 catalyzed reaction) and B10 neutron capture boosting. But high efficiency tritium production requirements are avoided, no additional lithium first wall technology needed for development. D-He fueled reactors would be reserved for mobile low neutron producing reactors like in ships or spacecraft. Obviously, the grid D-D reactors would have to far exceed the mobile aneutronic reactors in total power production in order to provide the needed He3.

I think that this depends on how they do it. I agree that D+D or TCD is certainly preferable over D+T since the whole tritium breeding thing is rather annoying. I still think that D+He3 is important though since it will lower the cost of the total energy produced. Plus, I believe that D+He3 plants can be closer to the consumer and are interesting for smaller communities.

There are only two reasons to pursue D-T reactions in my mind , the aforementioned psychological effects / bragging rights, and a high level of confidence that your system will only work with this easiest fuel.

I believe/ assume that this is why Park chose to use D+T for his first reactor design. Right now everyone wants to be the first to have "break even". Even JET is being refit with ITER tech for D+T experiments that they will hope will "demonstrate break even" a couple of years from now.
Of course, if you don't have a means in the reactor to actually extract and feed the energy back into it, the significance of it is IMHO more in the publicity than the actual practical use.

My bias is that the highly preferred goal should be a minimum of D-D fusion. D-T is highly suspicious option, in my mind at least, when talking about an economically viable, useful power production industry.

I think that there are very few reactor concepts that can make D+T work economically for the reasons you mentioned. Helion believes that they could, but they think that they don't have to. GF might be able to do it if they can get their reactor design to work as predicted. The new compact Tokamaks and derivatives like the Dynomak have a better chance than ITER does but I am not convinced. But maybe, just maybe they can be further optimized to handle D+D or TCD instead. From what I understand the Dynomak has a relatively high beta compared to traditional tokamaks.

[ladajo]

even possibly a D PB 11

Particle mass has a significant impact on core dynamics. Even 3He has as significant impact.
Depending on the design the loss considerations change significantly based on the particle in question.
This in turn impacts where Q>1 falls.
Any design will burn fuel, the question is efficiency to get Q>1.
Establishing burns of higher cross section fuels with easier to manage dynamics regarding loss rates would allow one to better understand the machine dynamics before attempting heavier fuels.
Current efforts are about proving the ability to establish conditions for Q>1. Not about jumping in on a production machine. Any noise towards that is just marketing.
No one as of yet has shown Q>1 conditions in a test.
I would pick the easiest fuel to do that, then leverage that knowledge to look at heavier / higher charge fuels.

[Skipjack]

No one as of yet has shown Q>1 conditions in a test.
I would pick the easiest fuel to do that, then leverage that knowledge to look at heavier / higher charge fuels.

That depends on how you look at it. D+T experiments cost a lot more since the reactor needs to either be serviced more and/or needs to be built to withstand it. If you just want to achieve the conditions to achieve a Q>1 with D+T then JT60 has already that with D+D (which would have been a Q>1 with D+T). If your reactor does not have the means to maintain the reaction and extract the energy, then this is really just for bragging rights. The almost 4 decades old JET will do that in a couple of years from now just to make sure funds keep rolling towards ITER. Note that JET wont be breeding tritium nor will it extract the energy and use that to keep the reaction going. So in the end it will be simply a math exercise.
Whether that is that much more useful than what JT60 did years ago to warrant the huge effort of refitting JET for prolonged D+T experiments, I don't know.

[bennmann]

Relevant to the discussion are simple, confirmed neutron counts. AFAIK, EMC and Park et al have the most promising history of neutron counts to date.

Those little bubbles make the evidence seeking part of my brain tingle. Having said that, it's almost a shame that info was missing from the cusp EMC paper.... I bet someone here has seen more recent numbers for that though...

Didn't Lerner do a burn recently...? Or was that just a kev test shot? Any neutron producing burns lately from any of the front runners anyone here knows about ?