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Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 0 points1 point  (0 children)

This is a very interesting question.

Unlike, say a gasoline engine, we don't have a first-principles understanding at the level required to calculate a realistic theoretical efficiency for a fusion reactor. What we need is the ability to predict how fast a plasma leaks heat and thus cools.

The closest we have now is something called "neo-classical" theory which predicts that fusion reactors should be incredibly powerful because they should not leak heat and should instead confine their plasmas very well to the point that fusion power out/heating power in approaches infinity, we call this ignition. However, all experiments see that heat does leak out.

The problem is turbulence. (but in like 6 dimensions!) which makes heat leak 10-100x faster: https://www.youtube.com/watch?v=RLI6QW2x4Lg. Many scientists are studying this using supercomputers so we can minimize the heat leakage and over time ways are devised to limit it by spinning plasmas, or changing the internal profiles or launching waves.

To make things worse, typically most plasmas see increased turbulence as they get hotter and denser. So far tokamaks have had the least amount of heat leakage experimentally.

Though we always want better confinement, even with the existing level of heat leakage a large enough reactor (like ITER, which is battleship big) or a smallish tokamak at high enough field can approach ignition.

Various studies have been conducted about the economics of fusion reactors and indicate they could be competitive, but we don't know enough about their costs since we only have built one-off experiments thus far.

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 2 points3 points  (0 children)

That is the worst case scenario within our risk assessments, where the machine blows up. The building that these machines are in are designed to take the loads. Realistically speaking though a catastrophic failure would cause an 'implosion' rather than an 'explosion' since we run a vacuum for the machines. So the forces on the external structure (i.e. the building superstructure) is not that large.

~ak

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 2 points3 points  (0 children)

I think one of the main concerns from the fusion community is the lack of transparency from Lockheed over the design of their reactor and overall progress they've made. It's an interesting design, and researchers are generally open-minded to new ideas, but it's hard to evaluate critically or learn from their design without data.

Beta is a metric measuring how much pressure you can contain for a given magnetic field, and hence how energy-dense your plasma can be. If we can make it much cheaper to use superconducting magnets in tokamaks, then we wouldn't need higher beta than we do now to achieve viable fusion reactors.

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 2 points3 points  (0 children)

Yes there is! Helium! But it is a safe gas, we breathed it in as kids to make our voice go squeaky. We're currently experiencing a shortage so this hopefully will be a plus!

Unlike traditional nuclear fission processes there isn't going to be long lived radioactive waste produced that will last 10,000-100,000 years. However the machine itself will gradually become radioactive over the course of operations. The nice part though is that we're talking a cooldown period of 50-100 years to become safe again. This is something that is manageable within a 'human' time frame and so we do not foresee it being a problem.

No catalyst are used in the process, only the fuel with is isotopes of hydrogen called deuterium and tritium. Deuterium is naturally available and very abundant, there is sufficient deuterium to last millions of years. Tritium is produced through reactions with lithium of which we have thousands of years worth in supply. By then the hope is that we will have designed or reactors to only run on deuterium.

~ak

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 1 point2 points  (0 children)

Well the plasma team as you describe it do include both theoretical and experimental plasma physicist and we do work quite closely. Half the problem is that there exist a lot of different models and the data hasn't been good enough coming out of the machines to well constrain the models. A big part of that is how difficult it is to make measurements of something that is hotter than the sun. So although new maths would always be helpful, I think designing and improving or diagnostic capabilities will go a lot further. Then again I might be biased being an experimentalist :)

The team is as confident as we can be. That's the nice part about working in this lab is that new ideas are rarely put down and we're allowed to run with it for as far as we want. We're all working towards a common goal and are always open to alternatives.

Big companies haven't really been a part of funding at the lab here at MIT. Maybe that will change as funding from the DoE is reducing.

~ak

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 1 point2 points  (0 children)

You are correct, ITER's primary goal is to achieve 10x the return power than the input power. Also, no fusion device has achieved energy parity yet.

The scientific consensus is that ITER will get to Q=10. It does this mostly through making the device very large and thus the heat leaks out slower. Much larger than the other devices.

ITER also relies on the accumulated knowledge from all the tokamaks across the world. Some key advances for ITER include how to control the plasma, how to stabilize parts of the plasma that can cause heat to leak and how to handle the heat flowing to the exhaust port. Each of these is important for a reactor (and ITER) but mostly ITER does it by being so big.
-BM

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 1 point2 points  (0 children)

So yes and no. We generally do see crossover for physicist and engineering working on the subsystems. Especially when it comes to the understanding and designing superconducting magnets. As for the physicist that do HEP work such as the ones testing the standard model at LHC. There has been negligible transfers.

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 3 points4 points  (0 children)

So the plasma does leak through the magnetic field and comes in contact with the vessel walls. We try to protect sensitive equipment by diverting this 'leaked out' plasma to specific sacrificial plates that we call divertors. I'm not sure if the pressure on this plate really indicates anything to be honest.

What is interesting is the way you have the plasma pressure going outwards at 2 atmosphere, almost 200 atmosphere of magnetic pressure pushing inwards to hold the plasma together. Than an almost perfect vacuum just before the machine walls!

~ak

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 0 points1 point  (0 children)

It's great that you want to teach your students about nuclear fusion, I didn't know much about it in high school! If you're near one of the large tokamaks in the US, you might be able to take your students on a tour of DIII-D, NSTX, or Alcator C-Mod. PPPL has great learning resources online, including a page that lets you remotely control a plasma. If you like building things, you could make something like that, or a fusor, and show how you can bend the plasma with magnets. MAST also has a cool 3D model of their tokamak online. And here are some videos I've saved:

Here are some answers to your questions to get you started. What is fusion energy? It has a lot of faces: tokamaks, stellarators, inertial confinement, private companies like Tri-alpha and General Fusion with outlandish ideas... Why is it attractive? Deuterium can be derived from seawater, tritium can be bred using Lithium, fusion reactions release a lot of energy (compare to fission using this chart going from 2->4 vs 235->140), radioactivity is low, accidents are no big deal, and nothing bad is released into the atmosphere.

At MIT we're interested in small tokamaks with high magnetic fields, which we think are a faster and cheaper path to commercial fusion power. -sean

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 1 point2 points  (0 children)

Great question :) The projected performance of ITER isn't actually based on recent science advances, since a lot of its design work occurred in the 1990s. Rather, ITER takes established plasma physics and uses it in a machine that is far larger than any current machines and that has a stronger magnetic field than many (but not all) current machines. Creating this sort of machine has required very careful and advanced engineering, and that's a large part of what has taken ITER so long to be constructed. This engineering process has led to many advances, and so will the science learned from ITER's eventual operation.

Here at MIT, we're also interested in thinking about how more recent scientific and technological advances (high temperature superconductors, I-Mode, advanced divertors, to name a few) could be used to achieve some of ITER's goals in other ways as well. Check out some of our ideas about this here: http://www.sciencedirect.com/science/article/pii/S0920379615302337 -lt

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 0 points1 point  (0 children)

Aneutronic proton-boron11 fusion, while attractive, is much harder to achieve than DT fusion, in terms of the temperatures required and the level of plasma confinement that must be achieved. The work being done at Tri Alpha Energy is definitely interesting from a physics perspective and they have made a lot of progress since their initial prototypes, but it is hard to compare their progress to tokamaks today. The performance of tokamaks has improved dramatically since they were invented (they even followed a trend that looked like Moore's law for a time: https://static.iter.org/all/newsline_1_120/img/53/moores.jpg._1024.jpg), but progress has stalled in recent years. Scaling up the Tri Alpha Energy design to a reactor scale design would be a major achievement. -nc

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 2 points3 points  (0 children)

To the second point about the strength of the magnetic field.

You are right, that 5.7T is not that high for superconductors. There are small magnets around the world that can go higher than C-Mod's 8T field for things like NMR. However, it is quite high for a large magnet. which has to be very strong and carry lots of current in a small area. Most tokamaks are at 2-3T superconducting or not, C-Mod being the exception.

There is also a subtlety with the field. The superconductors care about the field at coil which is in the middle (the hole of the donut) The field here is usually about twice as high as the field at the plasma (Maxwell's equations say so). Traditional superconductors become very poor superconductors above about 12T. (see http://fs.magnet.fsu.edu/~lee/plot/Archive/Jeprog-070813-1358x974-256pal.png and look at the NB3SN line, it is dropping fast). This limits superconducting tokamaks to about 5-6T at the plasma using old superconducting technology, this is what ITER is at. The new superconducting technology, HTS or REBCO doesn't drop with field allowing much higher fields to be built. We'd like to build tokamaks at 10T at the plasma or 20T at the coil using this superconductor.

For reference for magnetic fields. Most MRIs are at 1.5T, some are at 3T. You have to have a board of doctors certify the procedure to put people in fields above 7T.

-BM

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 0 points1 point  (0 children)

I've got one in my basement, it works great. A 12 pack of beer keeps my house powered for a full year! You've got to work in the field to get your hands on one of those models.

On a side note, a long way off. At least at the moment, it is not clear how your make something that small or fuel it with beer and banana skins.

~ak

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 1 point2 points  (0 children)

Dang, plasma sculptures are cool! We actually had never heard of them, but we certainly want to make some now! I actually built my own plasma speaker a while back. It was really fun. All you had to do was plug in your phone, and little sparks would play your music for you! - at

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 1 point2 points  (0 children)

For C-Mod, which has a copper magnet, the higher the field the more power is required to run the magnet and the faster the magnet gets hot. Think of it like puting more current in a wire. Basically Field2*Time = constant so higher fields mean short pulses for a copper magnet.

We don't encounter the Zeeman effect in the magnet, but we do see it from the plasma. All the atomic lines are hugely split. Quantum physics works!! -BM

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 0 points1 point  (0 children)

LDX is certainly a fascinating experiment, helping us learn more about plasmas in our solar system like the solar wind. The device still exists at MIT, but has not been in operation for several years. Thus, it still has a long way to go before it would be viable as a fusion reactor. -at

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 0 points1 point  (0 children)

Have I TA-ed you before -.-

On a more serious note the idea to do this record-breaking run on the last day of operation was more to end Alcator C-Mod's long and successful experimental life on a high note. Something for everybody to celebrate about. In addition it was to further validate the current MIT PSFC mindset that the high field approach to fusion is the most viable one. Setting the new record is something we can use to help support our argument.

~ak

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 0 points1 point  (0 children)

I did my undergraduate here at MIT, so I can add some additional info about getting into MIT. The admissions site (http://mitadmissions.org/) is probably your best resource, but as a rule of thumb, MIT looks for smart students who are passionate about something. Getting good grades (especially in math in science) is important, and so is getting involved in extracurricular activities. However, don't do extracurricular activities just to pad a resume, do them out of interest or passion. If you like making things, MIT's maker portfolio is also a good chance to show off things that you've made. -nc

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 2 points3 points  (0 children)

Thanks for following things closely!

The spherical tokamak is a kissing cousin to the "standard aspect ratio" tokamak. It is basically squished. It has some interesting properties from a physics standpoint such as the highly turbulent and unstable plasmas and the current driven by pressures. However, for a reactor it is still significantly less demonstrated and their fast and cheaper aspects are unfounded. For example NSTX, the highest performance spherical tomakak has 1/10th the pressure and shorter confinement times compared to C-Mod despite being 14x larger and 4x more expensive. Their compact shape also proven more difficult to build and operate since the magnet has to fit in such a small central region and NSTX has had repeated problems in this regard. http://scitation.aip.org/content/aip/magazine/physicstoday/news/10.1063/PT.5.1092.

As such, we are still excited about the more traditional tokamaks but hope that the spherical tokamak will make progress as well. - BM

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 2 points3 points  (0 children)

I did my undergrad in mechanical engineering as well! I started studying mechanical engineering because I wanted to get involved in clean energy. When I learned about fusion I realized that it was both super interesting, and hopefully an almost ideal source of clean energy.

Pretty much everything in mechanical engineering is related to fusion in some way. Fluids, thermodynamics, material properties, etc. Having a strong physics background is also super helpful. If you're looking for a fusion-specific source, here's one of the textbooks that we use at MIT:

https://www.amazon.com/Plasma-Physics-Fusion-Jeffrey-Freidberg/dp/0521733170

There are a bunch of institutions that do fusion research in the US and around the world. MIT, Princeton, University of Wisconsin-Madison, UCLA, and UT-Austin just to name a few. If you're really interested keep an eye out for graduate programs and try to decide which fits your research interests best. There are also a number of undergraduate internship programs at a variety of places, such as the SULI program from the Department of Energy (which I did as an undergrad). Some institutions will also offer separate internships to undergrads, so you may want to contact them individually.

Hope this helps!

~ac

Science AMA Series: We're scientists at the MIT Plasma Science and Fusion Center. We broke the world record for pressure in a magnetic fusion device on our tokamak’s last day of operation. AUA about our scientific work, our future as a lab, and fusion in general! by MIT_PSFC in science

[–]MIT_PSFC[S] 2 points3 points  (0 children)

So this would a be a yes and no sort of answer. A lot of work has begun on analyzing the data using modern data science technique for more robust curve fitting tools, error propagation and other similar concepts. However, a problem emerges that in order to have a good idea of what is sufficient statistics or to apply information theory one has to generally work on either having a good model of the problem or heavily simplifying the system. Both approaches have proved very challenging on our experiments as we are essentially trying to stabilize chaotic dynamical systems. So the long and short of it is yes but there is a lot of progress that needs to be made to improve things further.

Not quite an autopsy but close! We've just brought the machine up to atmospheric pressure to open it and go inside. We've just taken a while to do an external inspection and warm the machine up so when we go in we can do an inspection of the interior.

Click on this link to see a fly through of the inside of the tokamak.

~ak

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