Net Positive Fusion Reaction

[Ser Scot A Ellison]

I’m always skeptical when I hear people touting Fusion as a panecea… it seems like something that is always “20 years away” regardless of when we look at it.  However there is now a report of an artificially created fusion reaction creating a net positive energy output.  It was a brute force ignition done with several hundred lasers focused on the same point and not a sustainable reaction.

Can others with more physics accumune than I possess comment about whether this is really something to be excited about or if this is another … nothing burger?

Will the latest breakthrough in nuclear fusion help to fight climate change?  - https://www.npr.org/2022/12/13/1142208055/nuclear-fusion-breakthrough-climate-change

[Fez]

I do not have a physics background. But it seems to me that this is a big deal and that we're still decades away from it having a direct impact on commercial energy production. Seems like it's an important step forward.

[Sophelia]

That's pretty much what the BBC article says as well (with soundbites from a couple of UK profs).

[Kalbear]

Yeah, it's a good step forward but it isn't meaning that fusion is around the corner. It's still a highly energy-intensive process that requires a number of complicated steps to effectively sustain it for long periods of time - shooting hundreds of lasers a second while hundreds of these pellets drop into the chamber and then clear the debris field afterwards is a very difficult thing to do!

But at the same time we created a fusion reaction with lasers. A side effect is that we can now test thermonuclear reactions without having to detonate a bomb, which is kind of cool. 

[SpaceChampion]

 

[SpaceChampion]

 

[JGP]

29 minutes ago, Kalnestk Oblast said:

But at the same time we created a fusion reaction with lasers. A side effect is that we can now test thermonuclear reactions without having to detonate a bomb, which is kind of cool. 

Very cool.

 

3 minutes ago, SpaceChampion said:

 

Capitalization of the technology [not monetary, mind] and mass production being huge hurdles. 

I'm trying to keep my hopes about this realistic.

[Ser Scot A Ellison]

On 12/13/2022 at 1:50 PM, JGP said:

Very cool.

 

Capitalization of the technology [not monetary, mind] and mass production being huge hurdles. 

I'm trying to keep my hopes about this realistic.

Absolutely.  The NPR report makes the point that being a “brute force ignition” means a mechanism for continuing the reaction would be necessary and that’s really difficult.  That said I have always been skeptical we’d get this far… net positive energy output is a big deal.

[Spockydog]

 

[IFR]

This is a breakthrough, but as Kalnestk Oblast pointed out, and as the researchers explicitly delineate, this is primarily of interest to weapon stewardship.

In order for fusion to occur, nuclei must overcome the force of Coulombic repulsion. This can be achieved at degrees of 100s of millions of degrees Celcius. The fusion cross-section of deutrerium and tritium is very large, and so it only requires about 20-40 kiloelectronvolts per fusion event, and generally fusion is achieved with those isotopes at 100 million degrees Celsius. Thermonuclear devices use what is known as the Tellar-Ulam staging. A conventional fission explosion is initiated. The explosion has kinetic energy and particles that with high velocity that very shortly will blow apart the fuel, and thermal energy that will rapidly expand everything. However, the soft x-rays emitted from the plasma of the fuel traval faster, at the speed of light. The x-rays are channeled to the fusion fuel before any of the kinetic energy can reach it. The energy deposition by x rays onto the tamper surrounding the fusion fuel super heat the tamper, causing its outer shell to expand and the inner shell to compress. The rapid compression is the implosion mechanism. The inner shell compresses the fusion fuel to a very high temperature - about a hundred million degrees Celsius. This process is called radiative ablation. This initiates the fusion sequence of the staging.  Other stagings are also possible, so you can a large sequence of energy releases, limited only by how large you're willing to make your weapon and whether you are able to overcome the technical difficulties of increased complexities.

The indirect inertial confinement approach uses laser initiated radiative ablation to achieve fusion. A laser beam is directed at a metal or high Z target (I believe gold in this instance) and superheats the material. The plasma electrons then emit x-ray radiation at a target (a symmetrical diamond shell containing the DT fusion material). And just like with the bomb, radiative ablation causes the DT fuel to reach about 100 million degrees Celsius. This occurs in about a billionth of a second, and in this particular experiment, 4% of the DT was burned. It's a very complicated process, because while ablative heating is rapidly increasing the temperature of the material, and fusion events and high velocity alpha particles are contributing to futher heating, the material is simultaneously radiating x-rays, which is cooling the material. So it's a bit of a race, as you have to maintain that heat despite the material's tendency to cool itself.

As has been noted in this thread, there were several inefficiencies (since this experiment was designed for the study of equations of state and thermonuclear weapons). The 300 megajoules (or about 83 kilowatt hours) were required as input energy. Electricity had to be provided to operate the lasing mechanism. Further, since this was indirect, much energy was lost in the conversion of the infrared laser to x-ray radiation. This was not intended as a prototype to some eventual commercially viable design. As I understand it magnetic confinement is believed to be more viable for commercial use in the very, very distant future.

But it is a heartening display of ingenuity, and a demonstration that energy gain fusion is possible.

[Erik of Hazelfield]

That’s what I suspected. This breakthrough is to fusion power plants as hot air balloons were to the Wright brothers- proof that humans could fly, sure, but not in any practical way helping with the design of an aeroplane.

[Larry of the Lawn]

11 hours ago, IFR said:

This is a breakthrough, but as Kalnestk Oblast pointed out, and as the researchers explicitly delineate, this is primarily of interest to weapon stewardship.

In order for fusion to occur, nuclei must overcome the force of Coulombic repulsion. This can be achieved at degrees of 100s of millions of degrees Celcius. The fusion cross-section of deutrerium and tritium is very large, and so it only requires about 20-40 kiloelectronvolts per fusion event, and generally fusion is achieved with those isotopes at 100 million degrees Celsius. Thermonuclear devices use what is known as the Tellar-Ulam staging. A conventional fission explosion is initiated. The explosion has kinetic energy and particles that with high velocity that very shortly will blow apart the fuel, and thermal energy that will rapidly expand everything. However, the soft x-rays emitted from the plasma of the fuel traval faster, at the speed of light. The x-rays are channeled to the fusion fuel before any of the kinetic energy can reach it. The energy deposition by x rays onto the tamper surrounding the fusion fuel super heat the tamper, causing its outer shell to expand and the inner shell to compress. The rapid compression is the implosion mechanism. The inner shell compresses the fusion fuel to a very high temperature - about a hundred million degrees Celsius. This process is called radiative ablation. This initiates the fusion sequence of the staging.  Other stagings are also possible, so you can a large sequence of energy releases, limited only by how large you're willing to make your weapon and whether you are able to overcome the technical difficulties of increased complexities.

The indirect inertial confinement approach uses laser initiated radiative ablation to achieve fusion. A laser beam is directed at a metal or high Z target (I believe gold in this instance) and superheats the material. The plasma electrons then emit x-ray radiation at a target (a symmetrical diamond shell containing the DT fusion material). And just like with the bomb, radiative ablation causes the DT fuel to reach about 100 million degrees Celsius. This occurs in about a billionth of a second, and in this particular experiment, 4% of the DT was burned. It's a very complicated process, because while ablative heating is rapidly increasing the temperature of the material, and fusion events and high velocity alpha particles are contributing to futher heating, the material is simultaneously radiating x-rays, which is cooling the material. So it's a bit of a race, as you have to maintain that heat despite the material's tendency to cool itself.

As has been noted in this thread, there were several inefficiencies (since this experiment was designed for the study of equations of state and thermonuclear weapons). The 300 megajoules (or about 83 kilowatt hours) were required as input energy. Electricity had to be provided to operate the lasing mechanism. Further, since this was indirect, much energy was lost in the conversion of the infrared laser to x-ray radiation. This was not intended as a prototype to some eventual commercially viable design. As I understand it magnetic confinement is believed to be more viable for commercial use in the very, very distant future.

But it is a heartening display of ingenuity, and a demonstration that energy gain fusion is possible.

Exactly!

[The Anti-Targ]

What worries me with all this uncontextual net positive talk is that while the achievement is impressive the misinterpretation of its meaning to our ongoing energy question could be a distraction from energy solutions that are available now, improvable in the short term and can get us off fossil fuel dependence rather quickly if the policy commitment and investments are made.

By all means invest in fusion research, but please don't divert funding away from current non-fossil fuel energy solutions in some mis-guided belief that fusion electricity generation is almost here.

[Deadlines? What Deadlines?]

All that money being invested in fusion energy would be better spent building geothermal plants. Carbon neutral (if done right), no fossil fuels, and an inexhaustible energy supply suitable for base-load power generation. CHP plants would be ideal for colder climates. 

2 problems with geothermal: 

1. It's very capital intensive. While operational costs may be very low, the $/KW of building the plants is very high. All of the operational geothermal plants I'm aware of are on the smaller side (well under 1GW), and power generation of this kind tends to benefit massively from economies of scale. It's possible no one's hit the sweet spot with regard to plant size.

This is not a trivial point. Large scale power plants cost a lot of money to build maintain and the business case often involves predictions of what the price of electricity will be years or decades down the road. 

2. There's really no new science or technology that needs to be invented to make it work. Therefore, it isn't sexy. 

Regarding fusion energy, I'm also reminded of this:

https://thebulletin.org/2017/04/fusion-reactors-not-what-theyre-cracked-up-to-be/

I can't evaluate some of the technical claims but this guy seems credible. Maybe he's talking out of his ass; I dunno.

Even if (big if) all the technical hurdles can be overcome, the economics will kill it. 

[The Anti-Targ]

We generate about 7500GWh from 19 goethermal power stations and there is going to be a 51MW station built in the next few years to make it 20. About 15% of our electricity is geothermal.

[Spockydog]

15 minutes ago, The Anti-Targ said:

We generate about 7500GWh from 19 goethermal power stations and there is going to be a 51MW station built in the next few years to make it 20. About 15% of our electricity is geothermal.

It's all fun and games until Sauron diverts a magic river underneath Rangitoto and turns New Zealand into Mordor.

For realz this time.

[The Anti-Targ]

Yes, well, that would solve global warming at a local level with the sun being blotted out, it would be pretty cold here for a while. A bit hard to live without any sunlight though.

It would have to be a very magic river too, since Rangitoto is an island volcano in the Hauraki gulf.

[IFR]

6 hours ago, Deadlines? What Deadlines? said:

Regarding fusion energy, I'm also reminded of this:

https://thebulletin.org/2017/04/fusion-reactors-not-what-theyre-cracked-up-to-be/

I can't evaluate some of the technical claims but this guy seems credible. Maybe he's talking out of his ass; I dunno.

Even if (big if) all the technical hurdles can be overcome, the economics will kill it.

That's a good article, and the author is not talking out of his ass.

However, I do think that some of the concerns are overstated. The parasitic energy requirements are something I view as beneficial. One of the major problems with a fission reactor is that you can't simply shut it down. The moment you scram a reactor, even though the chain reaction ceases, you still have to deal with the thermal energy from the radioactive decay of the fission products, which is about 6.5% of the thermal energy before scramming. This can be contained in small reactors, but when you're generating gigawatts of power, 6.5% requires continuous cooling. A reactor that shuts down if there are any serious problems is something I see as an advantage, regardless of the loss of energy output.

The damage of materials due to high energy neutron flux is a valid concern. An incident neutron can be scattered by the nucleus it encounters; in this process, it may displace the lattice structure of that molecule. This gradually erodes the material. Another effect of neutron interaction with matter is the absorption of neutrons. Carbon-13 is a stable isotope, for instance. If carbon-13 absorbs a neutron, it becomes radioactive carbon-14. This is called "activating" the material. Different isotopes have different cross sections (or "likelihood of a particular interaction") for neutron absorption. So it is desirable to use materials with low cross sections of neutron absorption (in addition to other characteristics such as tolerance to high temperatures).

In ITER at least, the low level activity is also short-lived, with most radioisotopes with half-lives of 10 years or less. Which is extremely good, compared to the way the US handles its waste (non-processes, and so the waste has radioisotopes with half-lives in the thousands of years).

The issue of plutonium production is an interesting point. I'm not entirely sure, but I find myself doubting that this is an ideal method of production. With regards to the usefulness of plutonium for a weapon, there are grades, and this is evaluated on how pure the plutonium is. Pu-239 is the desirable isotope. It easily fissions at most energy levels, it has comparably low radioactivity, it generates low thermal energy (an important property in the metallurgical requirements), and it has a low likelihood of self-fissioning (which can cause pre-detonation and a much lower than desired yield). Weapon grade plutonium is very pure. Reactor grade plutonium is much less pure. The high neutron energy of the fusion neutrons is desirable in creating pure plutonium, but I suspect (but can't say for sure) that the very high neutron flux would be a problem. Still, plutonium production would absolutely be possible.

The major problem of that article is that fusion is still many decades away, and these technical difficulties are certainly not insurmountable. I can easily see a lot of future advancements mitigating the problems. 

But it is good to point out that every approach to energy generation has its own set of problems.

[Deadlines? What Deadlines?]

6 hours ago, The Anti-Targ said:

We generate about 7500GWh from 19 goethermal power stations and there is going to be a 51MW station built in the next few years to make it 20. About 15% of our electricity is geothermal.

Yeah, for some reason Indonesia has a lot of geothermal power generation. 

ETA: would I be correct in thinking NZ doesn't have much in the way of domestic fossil fuel resources? That's one of the reasons Iceland got into it; they'd have to import coal otherwise. They also give a shit about their ecosystem and managing coal ash is something they'd rather not deal with. Iceland also has the advantage of not having to drill too deep to hit hot rock.

[Deadlines? What Deadlines?]

2 hours ago, IFR said:

That's a good article, and the author is not talking out of his ass.

However, I do think that some of the concerns are overstated. The parasitic energy requirements are something I view as beneficial. One of the major problems with a fission reactor is that you can't simply shut it down. The moment you scram a reactor, even though the chain reaction ceases, you still have to deal with the thermal energy from the radioactive decay of the fission products, which is about 6.5% of the thermal energy before scramming. This can be contained in small reactors, but when you're generating gigawatts of power, 6.5% requires continuous cooling. A reactor that shuts down if there are any serious problems is something I see as an advantage, regardless of the loss of energy output.

I'm not sure what you're talking about here. Heat is going to be a problem in any kind of plant that uses thermal energy to make power. This is why you have things like emergency venting of superheaters (to keep them from melting) or three element feedwater control (to keep it from tripping). Giant steam turbines have barring (turning) devices to keep them rotating during shutdown to prevent the shaft from hogging or sagging.  I'm only slightly familiar with nuclear plants but I imagine it's similar.

What he's talking about is the parasitic losses that will effect overall plant efficiency; which in turn will determine the feasibility of this concept. That's a ways down the road but still. 

Speaking of "down the road", here's another one: turn down ratio. Any power plant has to be able to not only meet power requirements during peak demand, but also respond to changes in demand throughout the day. If the power delivery doesn't match the load, the system crashes. Hydro electric plants are great at this because they can meter the mass of water going through their turbines very quickly. Fission plants (my understanding) can also be turned down fairly easily by controlling the rate of fission. It isn't instant, because there's a lot of thermal energy in the system and changing it is like turning a battleship.

Plants that rely on burning of fuel also have good turn down ratios but, in extreme cases, you have to worry about combustion stability. Turn it down so much that combustion becomes unstable. If the fire goes out you've got assholes in blue coveralls running around like they're looking for the antidote. 

So, we're fifty yeas down the road, you've got a shiny new fusion reactor built, it's running perfectly fine, and the would be plant manager says, "OK, now show me that 75% looks like." I doubt these guys are even thinking about this yet, but if achieving a stable reaction takes this much work, you have to ask yourself if this thing only has one speed. If it does, it's kind of useless.