A new approach to Fusion

[rhoenix]

General Fusion, a startup in Vancouver, Canada, says it can build a prototype fusion power plant within the next decade and do it for less than a billion dollars. So far, it has raised $13.5 million from public and private investors to help kick-start its ambitious effort.

Unlike the $14 billion ITER project under way in France, General Fusion's approach doesn't rely on expensive superconducting magnets--called tokamaks--to contain the superheated plasma necessary to achieve and sustain a fusion reaction. Nor does the company require powerful lasers, such as those within the National Ignition Facility at Lawrence Livermore National Laboratory, to confine a plasma target and compress it to extreme temperatures until fusion occurs.

Instead, General Fusion says it can achieve "net gain"--that is, create a fusion reaction that gives off more energy than is needed to trigger it--using relatively low-tech, mechanical brute force and advanced digital control technologies that scientists could only dream of 30 years ago.

It may seem implausible, but some top U.S. fusion experts say General Fusion's approach, which is a variation on what the industry calls magnetized target fusion, is scientifically sound and could actually work. It's a long shot, they say, but well worth a try.

"I'm rooting for them," says Ken Fowler, professor emeritus of nuclear engineering and plasma physics at the University of California, Berkeley, and a leading authority on fusion-reactor designs. He's analyzed the approach and found no technical showstoppers. "Maybe these guys can do it. It's really luck of the draw."

The prototype reactor will be composed of a metal sphere about three meters in diameter containing a liquid mixture of lithium and lead. The liquid is spun to create a vortex inside the sphere that forms a vertical cavity in the middle. At this point, two donut-shaped plasma rings held together by self-generated magnetic fields, called spheromaks, are injected into the cavity from the top and bottom of the sphere and come together to create a target in the center. "Think about it as blowing smoke rings at each other," says Doug Richardson, chief executive of General Fusion.

On the outside of the metal sphere are 220 pneumatically controlled pistons, each programmed to simultaneously ram the surface of the sphere at 100 meters a second. The force of the pistons sends an acoustic wave through the lead-lithium mixture, and that accelerates into a shock wave as it reaches the plasma, which is made of the hydrogen isotopes deuterium and tritium.

If everything works as planned, the plasma will compress instantly and the isotopes will fuse into helium, releasing a burst of energy-packed neutrons that are captured by the lead-lithium liquid. The rapid heat buildup in the liquid will be extracted through a heat exchanger, with half used to create steam that spins a turbine for power generation, and the rest used to recharge the pistons for the next "shot."

The ultimate goal is to inject a new plasma target and fire the pistons every second, creating pulses of fusion reactions as part of a self-sustaining process. This contrasts with ITER, which aims to create a single fusion reaction that can sustain itself. "One of the big risks to the project is nobody has compressed spheromaks to fusion-relevant conditions before," says Richardson. "There's no reason why it won't work, but nobody has ever proven it."



He says it look longer than expected to raise the money for the prototype project, but the company can now start the first phase of building the test reactor, including the development of 3-D simulations and the technical verification of components. General Fusion aims to complete the reactor and demonstrate net gain within five years, assuming it can raise another $37 million.

If successful, it believes it can build a grid-capable fusion reactor rated at 100 megawatts four years later for about $500 million, beating ITER by about 20 years and at a fraction of the cost.

"I usually pass up these quirky ideas that pass my way, but this one really fascinated me," says Fowler. He notes that there are immense challenges to overcome, but the culture of a private startup may be what it takes to tackle them with a sense of urgency. "In the big programs, especially the fusion ones, people have gotten beat up so much that they've become so risk averse."

General Fusion's basic approach isn't entirely new. It builds on work done during the 1980s by the U.S. Naval Research Laboratory, based on a concept called Linus. The problem was that scientists couldn't figure out a fast-enough way to compress the plasma before it lost its donut-shaped magnetic confinement, a window of opportunity measured in milliseconds. Just like smoke rings, the plasma rings maintain their shape only momentarily before dispersing.

Nuclear-research giant General Atomics later came up with the idea of rapidly compressing the plasma using a mechanical ramming process that creates acoustic waves. But the company never followed through--likely because the technology to precisely control the speed and simultaneous triggering of the compressed-air pistons simply didn't exist two decades ago.

Richardson says that high-speed digital processing is readily available today, and General Fusion's mission over the next two to four years is to prove it can do the job. Before building a fully functional reactor with 220 pistons on a metal sphere, the company will first verify that smaller rings of 24 pistons can be synchronized to strike an outer metal shell.

Glen Wurden, program manager of fusion energy sciences at Los Alamos National Laboratory and an expert on magnetized target fusion, says General Fusion has a challenging road ahead and many questions to answer definitively. Can they produce spheromaks with the right densities, temperature, and life span? Can they inject two spheromaks into opposite ends of the vortex cavity and make sure they collide and merge? Will the acoustic waves travel uniformly through the liquid metal?

"You can do a good amount of it through simulations, but not all of it," says Wurden. "This is all very complex, state-of-the-art work. The problem is you're dealing with different timescales and different effects on materials when they're exposed to shock waves."

Los Alamos and General Fusion are collaborating as part of a recently signed research agreement. But Richardson isn't planning on a smooth ride. "The project has many risks," he says, "and we expect most of it to not perform exactly as expected." However, if the company can pull off its test reactor, it hopes to attract enough attention to easily raise the $500 million for a demonstration power plant.

Says Fowler, "Miracles do happen."

It looks as if development of this particular approach is proceeding apace, which is good to see. Are there any experts here who can shed some light here on the plausibility of this approach?

[Narkis]

Interesting. I hope this works, but I doubt it will. Spheromaks have been rejected by most of the experts in favour of the more traditional Tokamak. The experiments were short running and left many questions unanswered, iirc. Still, I don't know enough physics yet to give any reason on why it should or shouldn't work.. Ask me again in a few years, after I've gotten my degree.

[Feil]

Look, another person promising "Fusion in ten years". I hope they get their funding so that they can generate new knowledge pushing us towards the eventual realization of a fusion reactor... but I sure as hell wouldn't invest in them.

[BR7]

Are there any experts here who can shed some light here on the plausibility of this approach?

I'm not an expert, so I can't offer a numerical analysis, but the idea is pretty simple. The HUGE problem, I think, is getting enough uniformity in the shockwave to achieve compression sufficient for fusion. A similar task is hard enough to do with machined explosive lenses that nuclear tests sometimes fail. With the fluid used here, it should still be possible, but complications like turbulence, gravity, etc. make me very skeptical that this would work as described.

[Memnon]

There's a more in-depth article at Popular Science, at least with regards to background. It looks interesting, and if it works, then we're pretty much in the clear on a lot of things - as with any non-tokamak fusion scheme.

[Zixinus]

There is an entire subculture dedicated to creating fusion easier than the tokamaks. That's how expensive that damn thing is. Like with any other scheme, I hope it works, because if it does, it would certainly help solve energy production problems.

[Crossroads Inc.]

For those way smarter then I... I wish to ask, what if it is simply "impossible" to create a Fusion reactor that is economical? The dream of Fusion power is getting more out of it then you put it, what if its simply impossible?

[Sarevok]

Then you just really on the giant pre existing natural fusion reactors called "stars" and supplement it with other forms of energy.

[BR7]

what if it is simply "impossible" to create a Fusion reactor that is economical? The dream of Fusion power is getting more out of it then you put it, what if its simply impossible?

Getting more out than you put in is just a math problem*. Set up the right parameters, and you're set. How economical that is depends on available technology and demand, and is the big unknown, but there's little doubt that it can be done from an engineering standpoint.

*That graph is from here. The particular numbers are questionable, but it shows how increased temperature (to a point) and better confinement increase gain.

[Darth Wong]

what if it is simply "impossible" to create a Fusion reactor that is economical? The dream of Fusion power is getting more out of it then you put it, what if its simply impossible?

Getting more out than you put in is just a math problem*. Set up the right parameters, and you're set. How economical that is depends on available technology and demand, and is the big unknown, but there's little doubt that it can be done from an engineering standpoint.

That's a silly thing to say. All engineering problems are applied science problems which can be described in terms of math. That doesn't mean something which can be reduced to a math problem is necessarily a solvable engineering problem. You can't just wish the desired process parameters into existence.

[Simon_Jester]

For those way smarter then I... I wish to ask, what if it is simply "impossible" to create a Fusion reactor that is economical? The dream of Fusion power is getting more out of it then you put it, what if its simply impossible?

Then we have to rely on other power sources, which is kind of a shame, because most of them are either low-density and not very suitable for things like interstellar flight (solar), or non-renewable.

But I don't think it's time to give up hope yet. We have a much better idea of the scope of the problem now than we did sixty years ago, and defining a problem precisely is at least a prerequisite for solving it. So we're still making progress, and we still haven't ruled the idea out.

[BR7]

Getting more out than you put in is just a math problem*. Set up the right parameters, and you're set. How economical that is depends on available technology and demand, and is the big unknown, but there's little doubt that it can be done from an engineering standpoint.

That's a silly thing to say. All engineering problems are applied science problems which can be described in terms of math. That doesn't mean something which can be reduced to a math problem is necessarily a solvable engineering problem. You can't just wish the desired process parameters into existence.

My point was that the physical requirements for energy gain from fusion are well-known, not mysterious. I didn't mean to imply that knowing the math like that necessarily allows something to be built, but in this case, for example, the folks at ITER seem to be confident enough on the engineering to secure billions in funding for a decades-long project. Besides that, it's already been done in thermonuclear weapons, so clearly, it can be done.

[Zixinus]

For those way smarter then I... I wish to ask, what if it is simply "impossible" to create a Fusion reactor that is economical?

Creating fusion is not the problem, but making it efficient is. Currently, only ITER made more energy than what's required to operate it and even that only for a few seconds (in heat).

Plasma dynamics are a bit iffy subject and there is a lot of undiscovered territory (or at least, an unknown amount). I recall that there were many fusion schemes that should have worked in theory but then something new comes up (this includes especially the tokamak, that was very promising at first).

It's not impossible, but as of yet very difficult. Money is a big problem, for one. There are a lot of promising projects receiving little or none at all funding. Then there are the issues of cooling the superconducters. One of ITER's mayor criticism is putting plasma-level heat source next to a supercooled one (well, with a layer of boron in-between, IRC).

It also breaks down the preferred reaction type. The most popular is deuterium with deuterium, as this reaction requires the least energy to happen. The problem with this reaction is that it only produces heat (as it makes neutrons), quite like a fission reactor. This doesn't make marketing easier.

[Starglider]

For those way smarter then I... I wish to ask, what if it is simply "impossible" to create a Fusion reactor that is economical?

Creating fusion is not the problem, but making it efficient is. Currently, only ITER made more energy than what's required to operate it and even that only for a few seconds (in heat).

I think you mean JET (Joint European Torus) as ITER is currently at the early construction stage (digging foundations for the main building last time I checked). ITER is targeting an energy gain factor of 10 (i.e. fusion plasma thermal output of 10 times the electrical power requirements of the containment and heating systems). A factor of 20 plus is thought necessary for a viable power station.

[Zixinus]

Yes, you are correct, I meant JET.

[Winston Blake]

Without being on the design team, it's impossible to accurately guess how likely this is to succeed. However, note that every major fusion scheme started out as a 'simple alternative' and ballooned into a monstrosity. Magnetically-confined fusion was meant to be 'simply' a matter of heating up a plasma hot enough inside a strong enough magnetic field - but then unforeseen instabilities arose, were solved, more arose, etc. IEC fusion was 'simply' a matter of mimicking hydrogen bombs on a smaller scale - but unforeseen instabilities in the evenness of beam hitting the pellet arose.

Now this project is taking a scheme which is already known to have great instabilities and intends to 'simply' artificially stabilise it with modern control systems technology. At first glance, this seems excessively optimistic.

what if it is simply "impossible" to create a Fusion reactor that is economical? The dream of Fusion power is getting more out of it then you put it, what if its simply impossible?

It's 'economically possible' in the sense that useful power can be produced. There was a plan in the 50s or 60s to drop thermonuclear bombs into massive underground salt domes. The extremely hot molten salt would retain heat very well, and would be a source of thermal power. IIRC, this was an entirely plausible way of extracting useful energy from nuclear fusion. I don't recall what the problem was, but I imagine a limited number suitable sites, inefficiency, fallout, and the destruction and contamination of (profitable?) salt reserves were probably reasons against it.

More relevantly, IIRC the problems of tokamak fusion are well-understood now, and ITER is planned to achieve Q=5 (5x energy out vs in) based on sound engineering calculations. Summary: it works, the downside is that you need to build >$100B superconducting cathedrals to make it work.

The most popular is deuterium with deuterium, as this reaction requires the least energy to happen.

You're thinking of deuterium-tritium.

[Zixinus]

You're thinking of deuterium-tritium.

*slaps forehead*

Duh, of course. It seems that I forgot even the basics over time.

[Fingolfin_Noldor]

I think some money should be poured into hybrid fusion/fission reactors instead.

http://ptonline.aip.org/journals/doc/PH ... 24_1.shtml

The article requires permission for reprint or copy, so I will just give the link.

[Ford Prefect]

The problem with this reaction is that it only produces heat (as it makes neutrons), quite like a fission reactor. This doesn't make marketing easier.

I'm not hugely familiar with the science of fusion, but isn't this true of all fusion except tritium fusion?

[Ford Prefect]

And by 'tritium' I obviously mean Helium 3 + Helium 3. Obviously.

[starslayer]

And by 'tritium' I obviously mean Helium 3 + Helium 3. Obviously.

3He fusion releases protons, which still have to be dealt with; however, with magnetic containment, they should stay within the fusion mass. To a certain extent, they can also become self-regulating and help produce more energy, as 3He + 4He -> 7Be + γ, then 7Be + e- -> 7Li + ν, and further 7Li + p -> 24He. A caveat comes in here because the 7Be electron capture has an extremely small cross section, and only becomes appreciable at extremely high temperatures (~1.5E7 K), much higher than we have been able to achieve.

Oh, and to answer the original question, yes, most fusion mechanisms release neutrons as part of the process. To my knowledge, the only fusion process which does not is the p-p chain (of which 3He fusion is a part).

[BR7]

A caveat comes in here because the 7Be electron capture has an extremely small cross section, and only becomes appreciable at extremely high temperatures (~1.5E7 K), much higher than we have been able to achieve.

Temperatures of ~1E8 K have been achieved in JET, and TFTR got to ~5.1E8 K. I haven't heard of 7Be electron capture being used though.

[starslayer]

Huh. I didn't know that; interesting. Well, we have the temperatures to be able to do fusion using pure hydrogen, but do we have the requisite density, and can we sustain those conditions? Those are big problems.