Ask MIT Researchers About Fusion Power

Nuclear fusion power is the process of fusing light nuclei together to release energy, and ultimately, to put electricity on the grid. Today, we have six researchers from MIT's Plasma Science and Fusion Center here to answer your questions about fusion power, tokamaks, and public support and funding in the U.S. for this research. The Obama Administration's budget request for fiscal year 2013 is paying for the U.S. share of ITER construction out of the domestic program, starting with the closure of the MIT fusion lab. The interviewees are ready to answer technical and policy questions, so don't be shy! And, as always, please break unrelated questions into separate posts. Read on for information about the researchers who will answer your questions.

Dr. Martin Greenwald is a Senior Scientist and Associate Director of the MIT Plasma Science and Fusion Center. His experimental work focuses on turbulence and transport, density limits, and pellet fueling of magnetically confined plasmas. More recently, Dr. Greenwald has been heavily involved with data management, computation, simulation, networks, and remote collaborations for fusion research.

Professor Ian Hutchinson is interested in plasma control in tokamaks, as well as spatially resolved measurements of the radiated power coming from the plasma. He is the author of the standard fusion textbook Principles of Plasma Diagnostics. Prof. Hutchinson also works on particle-in-cell simulations of astrophysical and laboratory plasmas.

Assistant Professor Anne White researches turbulence phenomena on the Alcator C-Mod tokamak, developing new diagnostics to resolve the small fluctuations which cause energy and particles to leak out. She is the recent recipient of the U.S. Department of Energy Early Career Award.

Professor Dennis Whyte pursues research into plasma–material interactions; that is, the way the hot plasma in a magnetic fusion reactor interacts with the surrounding solid materials walls. His team is also developing novel diagnostics for fusion nuclear science, which is critical as fusion reactors start producing power (and neutrons) over long periods of time.

Nathan Howard and Geoff Olynyk are Ph.D students on the Alcator C-Mod project. Nathan, who is in the final year of his studies, studies turbulent transport phenomena experimentally and through simulation. Geoff, in his fourth year, is working on disruption mitigation, which is a way to quickly and safely shut a tokamak plasma down in a few thousandths of a second.

Polywell fusion

[mknewman]

What do you think of the efforts at http://www.emc2fusion.org/ [emc2fusion.org] and http://www.talk-polywell.org/bb/index.php [talk-polywell.org] ? They seem to be making real, measurable and open results but the mainstream physics community seems to ignore this progress.

Power Loss Scenario in Alcator C-Mod?

[eldavojohn]

Not to raise any fears -- rather out of genuine curiosity -- what happens when the magnetic fields that hold the 90,000,000 degrees Celsius plasma in place fail or loser power on the Alcator C-Mod? I understand it's probably in prototype mode but what sort of safety advantages or disadvantages do Alcator C-Mod designs offer over conventional large scale designs? Does the plasma come into contact with the toroidal super conducting coil? Then what?

I think the most important question...

[monsted]

When will fusion power my house?

What's the problem in building the future.

[Bucc5062]

As a non-scientist, what are the biggest stumbling blocks for effective fusion reaction? is this truly throwing money down the energy hole, or are there verifiable, measurable benchmarks that lead us from one point to the next. Something like, we got x to work, now we need y, when we get y, we get z and then we get fusion. Is it technology holding us back, politics, or the science?

NIMBYA

[GeneralTurgidson]

How do you explain the safety/benefits of fusion to a generation of people terrified of nuclear anything?

lower limit on tokamak design

[gyepi]

Are there any good guesstimates on how small a tokamak-based fusion reactor (which produces more energy than consumes) can become? Theoretical limitations on size of the reactor would have obvious implications for pragmatic issues. AFAIK there is very little limitation on how small fission-based reactors can get.

What do the numbers really look like?

[Erich]

ITER is a hugely expensive project, and won't produce a commercially viable power generation system.

In a lot of areas where research is done on things which don't work yet -- rockets, bridges, transmission systems, etc -- there's a general idea of how things might be able to "scale up" to meet the goals.

Is tokamak fusion really in sight of being commercially viable source of energy? If we need unobtanium to make a commercially viable reactor, wouldn't it make sense to wait until the materials are viable before making even larger tokamaks? What do we learn from making these new, bigger, more expensive reactors?

Or are we trying to build ever-bigger spark gap transmitters as a way to make radio better? Maybe we should look at other schemes?

Or, alternatively, we know of a nice, large, gravity-fed fusion reactor fairly nearby, is the engineering simpler to harness energy from that on a large scale?

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IEC's / Fusor

[claytongulick]

Why aren't IEC reactors based on Farnsworth's designs taken more seriously? From what I understand, IEC's have been more effective at producing fusion, and they are cheap to build. People even build them in the garage [electricalfun.com]. From everything I've read, no one really takes the "fusor" seriously in the fusion science realm, and it's considered a dead line of inquiry. I've never understood why.

Will I live to see Fusion power available?

[Tragek]

Is fusion power going to be feasible in the next 60 years (extrapolating my expected lifespan)?

What level of investment would get fusion going?

[Tragek]

Do you think a program of the size of the Apollo program could kickstart fusion to general availability? Or would a rather smaller program suffice?

Patents

[Anonymous Coward]

Will patents get in the way of your research?

Future Prospects, Laymen Versus Experts

[Iskender]

From the outside fusion research looks like a desperate field that's always struggling with its fundamental research/engineering questions. I know more than most laymen: I know the reactions work, I know the sun is powered by (very slow) fusion, I know fusion reactors have produced at least around 50% return on the electricity put in. Still, it feels like it's possible it'll never work, even knowing that difficult problems take time to solve.

This is the outside view. What does the future of fusion look like when you experts look at it from the inside? Does it look like a gamble? Or does it look more like "just give us proper funding and we'll give you your reactor."?

Are Tokamaks practical?

[Anonymous Coward]

The late Dr. Bussard of EMC2 [emc2fusion. org] claimed that the fundamental concepts of Tokamak fusion did not provide a platform for cost-effective positive-return power reactors. With the enormous ITER project reactor still not expecting positive return, at what point, if ever, will Tokamak research benefit the power grid?

What could you do with unlimited resources?

[petes_PoV]

Given $1Tn, the pick of the best brains in the world to work willingly on the project, a large enough location away from any and all governmental regulation and every facility you could ever need - WHEN WILL IT BE COMMERCIALLY AVAILABLE?

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The talk is always about break-even with fusion

[circletimessquare]

But about capturing the power? Are we generating heat that will drive steam turbines?

What schemes to capture and harness the power exist?

Dense Plasma Focus

[mbradmoody]

Do you see any merit in the "dense plasma focus" approach to commercial fusion power production, specifically the work of the Lawrenceville Plasma Physics group?

Scaling of Tokamaks

[tp1024]

I haven't really found a concise statement on this so far. Assuming the current state of the art in plasma dynamics, how do fusion reactors scale with respect to size and magnetic field strength? Both in terms of the Q value of D-T reactions and D-D reactions. So, what happens when you scale up the size or magnetic field strength by a factor of 2?

(What Q values have been achieved with D-D fusion anyway? I've seen 0.7 for JET in a real-world D-T trial in 1997. What's typical fori D-D? How much effort does it take to get D-D to the current level of D-T?)

Expanding on this:

[Anonymous Coward]

Could you break down the various barriers/bottlenecks to the introduction of commerical fusion?

What are the technical problems in the state of the art, what other factors (political, economic, etc.) do you see at play?

How do you and your labs collaborate with others, and how is technology transferred? Is there much international cooperation?

Are there policy communities (China, India?) that might be more primed for the introduction of fusion technology into their grids than in North America? What would need to happen for North America to start using fusion?

I have many more questions, but those are the ones that popped into my head first. This is such a great opportunity -thank-you for taking the time today!

Infighting by fusion researchers?

[Medievalist]

Researchers studying different types of reactors (Bussard polywells, tokamaks, LENR like the Rossi eCat, Farnsworth fusors, etc.) seem to spend an inordinate amount of time making negative public statements about each others' work.

Are there any researchers outside your own field that have attacked your work? Do you see this as a problem? Is it an unavoidable consequence of trying to gain funding when fission is the favored technology? Does all non-fission research suffer when fusion researchers fight among themselves, or is this just part of the normal scientific debate?

NIF

[Grond]

Is the NIF approach even plausibly capable of generating electricity in a useful way, or is it purely a research platform / smokescreen for nuclear weapons research?

Re:Polywell fusion

[Rei]

It does not violate the 2nd law of thermodynamics beause it's not claiming to do so without energy. There is a constant energy input into the system. As Rider's work shows (Rider being the "scientist who showed..." that you mention), you can maintain fusion in a non-Maxwellian plasma but only if you selectively accelerate low energy ions instead of the bulk plasma.

Does Polywell do that? I doubt it, but I'm not versed enough to make a judgement.

Your Favorite Books?

[eldavojohn]

So I'm not a physicist (software guy) but I've taken a few physics classes. At an early age I found a tattered copy of George Gamow's One Two Three . . . Infinity [amazon.com] which, although incorrect in some parts (I guess that's why they revised it and that's why 'speculations' was in the title), was perfectly written for my then fifth grade mind. It set me on a path toward science and a few weeks ago I saw the same 1960s Viking Press edition and flipped through it noticing what was slightly off and remembering it. I've since grown to love other obvious books like Hawking, Penrose, Hofstadter, etc.

So, quite simply, what are your favorite books for all minds young and old? Also, can you annotate which are written for the layman's entry into the given field and which are written to encompass the field for the researcher? I find that some books start off with the jargon so strong and the references and footnotes so thick that you start to have to reread every paragraph as they're clearly condensing entire historic papers into lengthy sentences. Any fiction books worthy of influencing your work and desires?

Ranking different fusion concepts

[Anonymous Coward]

There are many potential routes to economic fusion. Assuming each of these concepts were funded at ITER levels, how would you rank the potential for economic fusion (cost competitive with nuclear) coming from each of the following concepts within the next 25-30 years:
1/ Field Reversed Configuration - eg Helion Energy, Tri Alpha
2/ Electrostatic Confinement - eg Polywell/EMC2
3/ Magnetised Target Fusion - eg General Fusion
4/ Laser Inertial Confinement - eg NIF, HiPER
5/ Heavy Ion Inertial Confinement - eg Fusion Power Corporation
6/ Tokamaks - eg ITER, DEMO
7/ Stellarator - eg Wendelstein 7-X
8/ Levitated Dipole - eg MIT LDX

Re:Dense Plasma Focus

[Dr_Barnowl]

I would mod up, but I have already commented.

Their reactor design is certainly the most elegant, being the only device I've seen that proposes collecting the energy in a solid-state manner, and not just boiling a damn great kettle like everything else. It's also one of the smaller scale devices, the design reactor fitting in a shipping container and projected to cost on the order of a million dollars rather than being in the billions, producing on the order of 5 MW, making it a shoe-in for military funding to prime the development pump (the military would go ape for something the size of a shipping container that can produce 5 MW without having to ship in diesel fuel).

It doesn't require rare and expensive tritium fuel. If their project manages to prove over-unity it would also seem to have the fewest engineer hurdles to becoming a commercial product, the difficulties mostly surrounding the construction of really fast high power switches, and an X-photoelectric collector.

Their operating budget is tiny compared to the likes of NIF and ITER as well ; it would be great to see even a few percent of these budgets distributed to alternative approaches.

If you could have anything you wanted...

[reovirus1]

If the president came to you and said, "We have a national emergency. We need this to become a viable form of energy as soon as possible. You have the entire resources of the nation available. I will use my executive powers to make it happen. Whatever resources, funding and people you need..." What kinds of things would you ask for? How long with the entire backing of a nation and the political will to make it happen would it take?

Focus Fusion / aneutronic fusion

[mwk88]

Focus Fusion Society http://focusfusion.org/ [focusfusion.org] is posting research on their project to do aneutronic e.g. Proton Boron (pB11) fusion. The concept sounds great, and as an engineer several parts of their design such as direct extraction of electric power are elegant. Is this credible research or pie-in-the-sky? I have not seen much mention in mainstream fusion research.

Re:Computational methods in plasma/tokamaks

[nthoward]

Hello, This is Nathan. Thanks for the question regarding the computational methods used in plasma physics/tokamak turbulence simulation. Let me try to answer your question. So my work actually focuses on turbulent transport model validation (the comparison of experimental measurement with computational models) in the core of tokamak plasmas. Fundamentally the difficultly with plasma simulation comes down to the fact that we have a large number of particles (~1x10^20 m^-3) which due to the long range nature of the electromagnetic force, affect the movement of every other particle in the plasma, at every point in time and operate on a wide range of time and spatial scales. Now there are some simplifications to that statement but I wont go into those here. In theory, the Newton-Maxwell set of equations, that is the combination of Newton's laws with Maxwell's equations can give you a complete description of all phenomenmom in the plasma. However, given the large number of particles and the long range nature of the forces involved, this problem is computationally intractable. The first step of simplification is taking a statistical approach to describing the particles in the plasma, that is, describing each population with a distribution function and tracking the evolution of the distribution function. This set of equations is known as the Maxwell-Boltzmann set of equations. However, this is a 6-D set of equations and we require some more simplifcation. To do this we basically elminate the motion of very fast time scales from this set of equations and say we are look at spatial scales which are relevant for microturbulence which drives the transport of heat, particles, etc. in the plasma. The resulting equation is called the gyrokinetic equation and it is thought to contain sufficient physics to simulation the microturbulence which is present in pretty much all plasmas. This is the cutting edge model for turbulence simulation in tokamaks. In these simulations you can see the development of turbulent eddies and structures which result in the transport of heat and particles out of the system on a time scale much shorter than that from purely collisions. Now, as you correctly noted, measurements in high temperature plasmas are indeed quite difficult to make and it is only in the last 10 years that both the models and the measurements have become accurate enough to make any meaningful comparision between the two. In other words, we are just now to the point where we can validate these models through comparison with experiment. To make things more difficult, the temperature profiles in plasmas are often observed to be "stiff". This means that the normalized gradients of these quantities are not easily changed. This arises from the fact that the plasma microturbulence is driven by free energy in the temperature and density gradients. As a result, if the gradient increases, the level of turbulence in the plasma does as well and this results in larger eddies and therefore larger loss of particles and energy from the system. This loss of energy tends to flatten the profiles and reduce the gradient. Therefore there is a critical value at which the turbulence is found to "turn on" and there is a profile shape which the plasma tends to relax to. This makes simulation difficult because it increases the sensitivity of the predicited heat/particle flux to the background plasma gradients. Since the gradients are derivatives of quantities which we measure, they are much more difficult to determine with great accuracy. My own work involves assessing the experimental error in many of the quantities that are driving plasma turbulence. With a proper assessment of the uncertainity in the measurement, I am able to deduce the sensitivity of the model's predictions to the uncertainity in the measurement and make a more meaningful statement of the model's ability to simulate experiment. I am sorry if that was a bit too rambling, but hopefully I at least partially answered your question. If you are interes