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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.
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.
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?
My work here is dung.
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?
Life is a great ride, the vehicle doesn't matter
How do you explain the safety/benefits of fusion to a generation of people terrified of nuclear anything?
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.
Attitudes make the difference between Space and Time: we want to MAX our temporal, and MIN our spatial extension.
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?
-- Erich
Slashdot reader since 1997
As practicing researchers, can you tell us about the health of the pipeline of young researchers coming into the field? Is there a glut of trained physicists at this stage, or is there still a need for trained specialists to enter the field, especially with ITER and follow-on machines coming online in the next couple of decades?
Will patents get in the way of your research?
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?
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!
Focus Fusion Society http://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.
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